Data Loading...
F2 - SCIENCE (DLP) Flipbook PDF
Text Book DLP Science Form 2 KSSM
108 Views
95 Downloads
FLIP PDF 85.4MB
KURIKULUM STANDARD SEKOLAH MENENGAH
SCIENCE FORM 2
Writers Jariah binti Khalib Maznah binti Omar Badariah binti Hamzah Shamsulikram bin Abdul Hamid Translators Ram Kumari K. Raman Yew Chian-Hauo Sharon Chelvi Moorthy Shirley Monica Editors Nadiatulaini binti Azenan Kumutha Murugiah Designer Mohd Fauzi bin Mohamad Hassim Illustrator Wan Hamizan bin Wan Hussin
2017
KEMENTERIAN PENDIDIKAN MALAYSIA SERIAL BOOK NO. : 0076 KPM2017 ISBN 978-967-14472-7-7 First Published 2017 © Ministry of Education Malaysia All rights reserved. No part of this publication may be produced, stored in any retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior permission of the Director General of Education, Ministry of Education Malaysia. Negotiation is subject to the calculation of royalty or honorarium. Published for Ministry of Education Malaysia by: Karangkraf Network Sdn. Bhd. Lot 2, Jalan Sepana 15/3, Off Persiaran Selangor, Seksyen 15, 40200 Shah Alam, Selangor Darul Ehsan. Telephone: 603-5101 3836 Fax: 603-5101 3685 Email: [email protected] Website: www.karangkraf.com Design and typesetting by: Karangkraf Network Sdn. Bhd. Font type: Minion Pro Font size: 11 pt. Printed by: Ultimate Print Sdn. Bhd. Lot 2, Jalan Sepana 15/3, Off Persiaran Selangor, Seksyen 15, 40200 Shah Alam, Selangor Darul Ehsan.
ii
ACKNOWLEDGEMENT The publisher would like to thank the following organisations and individuals for their invaluable assistance and cooperation in the preparation of this book: Committee members of Quality Control, Textbook Division, Ministry of Education Malaysia Curriculum Development Division, Ministry of Education Malaysia Officers of the English Language Teaching Centre (ELTC), Teacher Education Division, Ministry of Education Malaysia Dato’ Dr. Sheikh Muszaphar Shukor Al Masrie Sheikh Mustapha Datuk M. Magendran Datuk N. Mohanadas Datuk Dr. Mazlan Othman Universiti Perguruan Sultan Idris Nur Adlyka Ainul Annuar
C ontents v
Introduction
Theme 1: Maintenance and Continuity of Life Chapter 1 Biodiversity
2
1.1 Diversity of Organisms 1.2 Classification of Organisms Summative Practice 1
4 7 17
Chapter 2 Ecosystem
20
2.1 Energy Flow in an Ecosystem 2.2 Nutrient Cycle in an Ecosystem 2.3 Interdependence and Interaction Among Organisms and between Organisms and the Environment 2.4 Role of Humans in Maintaining a Balanced Nature Summative Practice 2
22 25
Chapter 3 Nutrition
44
3.1 3.2 3.3 3.4
Classes of Food Importance of a Balanced Diet Human Digestive System Process of Absorption and Transportation of Digested Food and Defecation Summative Practice 3
46 53 60
Chapter 4 Human Health
74
4.1 Infectious and Non-infectious Diseases 4.2 Body Defence Summative Practice 4
76 82 90
28 39 42
66 71
Theme 2: Exploration of Elements in Nature Chapter 5 Water and Solution
94
5.1 Physical Characteristics of Water 5.2 Solution and Rate of Solubility 5.3 Water Purification and Water Supply Summative Practice 5
96 106 113 121
Chapter 6 Acids and Alkalis
124
6.1 Properties of Acids and Alkalis 6.2 Neutralisation Summative Practice 6
126 133 137 iii
Theme 3: Energy and Sustainability of Life Chapter 7 Electricity and Magnetism
140
7.1 Electricity 7.2 Flow of Electric Current in a Series Circuit and Parallel Circuit 7.3 Magnetism Summative Practice 7
142 152
Chapter 8 Force and Motion
166
8.1 Force 8.2 Effects of Force Summative Practice 8
168 175 201
Chapter 9 Heat
204
9.1 9.2 9.3 9.4
Relationship between Temperature and Heat Heat Flow and Thermal Equilibrium Principle of Expansion and Contraction of Matter Relationship between Types of Surface of Object, and Heat Absorption and Emission Summative Practice 9
206 207 213
Chapter 10 Sound Waves
222
10.1 Characteristics of Sound Waves 10.2 Loudness and Pitch of Sound 10.3 Phenomena and Application of Reflection of Sound Waves Summative Practice 10
224 229 232 235
158 164
216 220
Theme 4: Earth and Space Exploration Chapter 11 Stars and Galaxies in the Universe
238
11.1 Stars and Galaxies in the Universe Summative Practice 11
240 249
iv
Chapter 12 Solar System
250
12.1 Solar System Summative Practice 12
252 266
Chapter 13 Meteoroid, Asteroid, Comet
268
13.1 Other Objects in the Solar System; such as Meteoroids, Asteroids and Comets Summative Practice 13
270 277
Answers Glossary Bibliography Index
279 284 287 288
I ntroduction T
he Science Form 2 textbook is written for Form 2 students based on the Standard-Based Curriculum and Assessment for Form 2 prepared by the Ministry of Education. This book is written with more emphasis on thinking skills, information and communication skills, decisionmaking and problem-solving skills so that students can master the skills needed in the 21st century. Additionally, STEM Teaching and Learning approach is incorporated through approaches such as inquiry, problem-solving and projects to elevate students’ interest towards science and technology. To achieve this objective, this book incorporates special features as follow:
8.2.2
My
World
Learning Standards based on the Standard-Based Curriculum and Assessment for teacher’s reference
Application of science in the daily life of students
My Malaysia!
Latest information regarding achievement of science in Malaysia
Formative Practice
Provides questions to test students’ understanding at the end of each subtopic
Today
in
History
Information regarding history of science Magical
SCIENCE
Appreciating the wonders of science
Science Additional information related to the topics
Brain
Teaser
Questions that challenge thinking
v
Various activities in this book: Experiment
Inquiry
Project
Types of activities
Discussion
Simulation
Technology
Visit
New features in this book:
21
st
Century
21st Century Skills Thinking & Problem-solving skills Interpersonal skills & Self-directed learning Information & communication skills
STEM STEM (Science, Technology, Engineering and Mathematics) As a teaching and learning approach which applies and integrates knowledge, skills and values of STEM through inquiry, problem-solving or projects in the context of daily life. This approach hopes to attract students’ interest to pursue STEM education in school and enter the STEM workforce to tackle challenges and be competitive globally.
STEM Career in STEM field (Science, Technology, Engineering and Mathematics) vi
Components at the end of a chapter:
1
Summary Summary of a chapter
Summative
3
Practice
Questions to test students’ understanding at the end of a chapter
2 SELF-REFLECTION Simple checklist of learning standards for students’ reference
HOTS
Mastery
Levels 5 and 6 HOTS questions
4
HOTS Questions (Applying, analysing, evaluating, creating)
Digital components in this book:
Download the free QR reader application from the App Store or Play Store
Video Video
Interactive quiz
Additional information
Quiz
Info vii
Guideline to scan AR for Three-dimensional Animations and Interactive Games Step 1 Download the free QR reader application from the App Store or Play Store.
Step 2 Download the free AR Buku Teks application by scanning the QR code below.
or
Accompanied by audio
Step 3
SCAN IMAGE
Find the pages that have these icons.
Threedimensional animations
SCAN IMAGE
Interactive games
Step 4 Scan the image on the page with your smartphone or tablet and enjoy the three-dimensional animations and interactive games. Three-dimensional animations
viii
Interactive games
1
Maintenance and Continuity of Life
to What is the importance of biodiversity ans? hum How can we maintain the balance of
nature?
lifestyle? Why is it important to have a healthy n our What are the practices that strengthe immune system?
1
Cha
er t p
1
Biodiversity
What is biodiversity? Why is it important to classify organisms systematically? How is biodiversity conserved?
Let’s understand: Diversity of organisms Classification of organisms
2
Chapter 1 : Biodiversity
Science Blog
SCIENCE BLOG The Rafflesia in Malaysia Malaysia is the habitat of the world’s largest flower, the rafflesia (Rafflesia sp.). The rafflesia is a parasitic plant that feeds on its host. The rafflesia gives off a rotting smell when in full bloom. This flower is also very unique because it does not have any leaves to carry out photosynthesis, nor does it have roots to absorb water and nutrients from the soil.
Keywords Biodiversity
Reptile
Vertebrate
Fish
Invertebrate
Amphibian
Mammal
Monocotyledon
Bird
Dicotyledon
3
1.1
Diversity of Organisms
D
id you know that our country, Malaysia, is one of the 12 megabiodiversity countries in the world? The equatorial climate of Malaysia makes it a very ideal habitat for a variety of organisms. Can you name the animals and plants shown in Photograph 1.1?
Diversity of animals and plants in Malaysia
Photograph 1.1 Diversity of animals and plants in Malaysia
Science
What is Biodiversity? The diversity of organisms, whether microorganisms, animals or plants, is known as biodiversity. Biodiversity exists as a result of the diversity of habitat and climate. Different organisms have different characteristics which enable them to adapt and thrive independently in their respective habitats (Photograph 1.2).
Desert
Polar regions
Biodiversity also covers diversity at the genetic level. Genetic diversity is the diversity within a species, based on variations in the genes of each microorganism, animal or plant.
Soil
Sea
Photograph 1.2 Diverse organisms in different habitats 4
1.1.1
Chapter 1 : Biodiversity
The Importance of Biodiversity
Today
in
Biodiversity is a priceless treasure and a legacy of nature which should be preserved. Can you list down some of the importance of biodiversity based on Photograph 1.3? Sources of food
Balance in nature
Cycle of nutrients, pollination and interaction between organisms create balance in nature.
Animals and plants supply food to humans.
History
The International Day for Biological Diversity is celebrated on the 22nd of May every year.
Recreational places
Areas that are rich in biodiversity can be developed as recreational places.
Medical
Raw materials for industries
Education
Herbs are widely used in the manufacture of medicines and cosmetics.
Timber, bamboo and rattan are examples of forest products which are used to make musical instruments, furniture and to build buildings.
Humans increase knowledge and create new technology through scientific research on microorganisms, animals and plants.
Photograph 1.3 Importance of biodiversity 5
Effective Biodiversity Management It cannot be denied that we need raw materials such as timber for development. Nevertheless, deforestation activities need to be controlled to preserve our biodiversity from extinction (Photograph 1.4). What methods can we use to maintain and conserve biodiversity? Biodiversity can be maintained and conserved by: • banning the killing or trade of endemic and endangered animals and plants through the Wildlife Protection Act 1972, • protecting the habitat through creating national parks, marine parks, forest reserves and wildlife sanctuaries, • undertaking reproductive programmes such as seedling nurseries to help with reforestation and turtle hatcheries.
A ctivity
Photograph 1.4 Deforestation activities cause animals to lose their habitat and food sources
Science
An endemic species is a species that lives in clusters within a restricted habitat in a specific location. Examples of endemic plants and animals in Malaysia include the rafflesia, pitcher plant (Nepenthes rajah), leatherback turtle, Malayan tiger and the Borneo Pygmy elephant.
Science
1.1
Aim: To conduct a discussion on effective biodiversity management. Instruction 1. Work in groups. 2. Find information on: (a) factors that cause the extinction of animals and plants (b) ways to preserve and conserve animals and plants including endemic and endangered species 3. Present your group findings in class.
The methods of biodiversity conservation can be classified as in situ conservation and ex situ conservation. In situ conservation, preserves the species within their natural habitat such as in national parks, permanent forest reserves and marine parks. Ex situ conservation, on the other hand, preserves the species outside of their natural habitat such as in zoos and botanical parks.
Biodiversity http://www.nre.gov.my
Formative Practice 1. 2. 3. 4.
6
1.1
Info
What is biodiversity? How does biodiversity contribute to the economy? What is an endemic species? Give two ways to preserve and conserve endemic species. Give examples of endangered species in Malaysia.
1.1.2
Chapter 1 : Biodiversity
1.2
Classif ication of Organisms
T
he two main groups of organisms are animals and plants. Animals and plants can be classified further into smaller groups based on their common and different characteristics. Study Photograph 1.5. What are the similarities and differences between the two animals? Photograph 1.5
Classification of Animals
Animals can be classified as invertebrates and vertebrates. Can you state the differences between these two groups of animals?
Invertebrates Invertebrates are animals without a backbone. Figure 1.1 shows the classification of invertebrates. Invertebrates Without legs Without segmented body
With legs
With segmented body
Three pairs of legs
More than three pairs of legs
Figure 1.1 Classification of invertebrates
Segmented body is the division of an animal's body into several segments.
Invertebrates Without Legs 1
Science
Without segmented body • There are invertebrates without legs and without segmented bodies.
Sponge
Sea anemone
Corals
Planaria
Snail
Photograph 1.6 Invertebrates without legs and without segmented bodies 7
2
With segmented body • Some invertebrates without legs have segmented bodies.
Tapeworm
Leech
Earthworm
Segment
Photograph 1.7 Invertebrates without legs with segmented bodies
Science Invertebrates With Legs
Insects are the largest group of animals. There are 950 000 species of insects.
Characteristics of invertebrates with legs: • have segmented bodies • have hard outer shells (exoskeleton) 1
Three pairs of legs
Ant
Butterfly Photograph 1.8 Invertebrates with three pairs of legs
8
Cockroach
Chapter 1 : Biodiversity
2
More than three pairs of legs
Spider
Horseshoe crab
Centipede
Prawn
Scorpion
Photograph 1.9 Invertebrates with more than three pairs of legs
Vertebrates Vertebrates are animals with a backbone (Figure 1.2). Vertebrates Fish
Amphibians
Reptiles
Birds
Mammals
Science
Figure 1.2 Classification of vertebrates
Fish Fish are animals with the following common characteristics: • poikilothermic • covered in hard and slimy scales • have fins and a tail • breathe through gills • lay eggs • undergo external fertilisation
A poikilotherm is an organism that has a body temperature that changes according to its surrounding temperature. A homeotherm, on the other hand, is an animal with a body temperature that is constant and free from the influence of its surrounding temperature.
Grouper Clown fish Eel Photograph 1.10 Examples of fish 1.2.2
9
Amphibians Amphibians are animals with the following common characteristics: • poikilothermic • live on land and in water • covered with moist skin • young amphibians breathe through gills • adult amphibians breathe using their lungs and moist skin • produce jelly-like eggs (spawn) without a shell • undergo external fertilisation
Salamander
Toad
Tadpole
Frog spawn
Frog
Photograph 1.11 Examples of amphibians
Reptiles Reptiles are animals with the following common characteristics: • poikilothermic • produce eggs with a shell • breathe through lungs • have scales and hard skin • undergo internal fertilisation Iguana
Turtle
Snake Photograph 1.12 Examples of reptiles
10
Crocodile
Chapter 1 : Biodiversity
Science
Birds Birds are animals with the following common characteristics: • homeothermic • covered with feathers to maintain body temperature • breathe through lungs • have wings that help some birds to fly • have a pair of scaly feet • undergo internal fertilisation • produce eggs with hard shell
The rhinoceros hornbill is a protected animal in Malaysia. It is the state bird of Sarawak.
SCAN IMAGE
Let's play
Owl
My Malaysia! Malaysia is a habitat for nearly 742 species of birds. At least 522 species are local species, 192 are migratory species and 52 are local species with migratory characteristics.
Kingfisher
Duck Photograph 1.13 Examples of birds
Mammals
Brain
Mammals are animals with the following common characteristics: • homeothermic • covered with fur or hair • breathe through lungs • undergo internal fertilisation • give birth and nurse their young
What is the difference between fur and hair?
Bat
Giraffe
Teaser
Elephant
Photograph 1.14 Examples of mammals
Lion 11
Classification of Plants Plants are classified as non-flowering and flowering plants. Plants
Non-flowering plants
Flowering plants
Science Non-vascular plants are simple and small plants without a vascular system.
Figure 1.3 Classification of plants
Vascular plants have a vascular system within them that transport water and food throughout the plant. These plants also have true roots, stems and leaves.
Non-flowering Plants Non-flowering plants consist of moss, fern and conifer. What are the common characteristics of each of these groups of plants? Non-Flowering Plants
Moss
• Reproduce by producing spores • Non-vascular
Fern
• Reproduce by producing spores • Vascular
Conifer
• Reproduce by bearing cones • Vascular
Figure 1.4 Classification of non-flowering plants 12
Chapter 1 : Biodiversity
Flowering Plants Flowering plants produce flowers which become fruits that contain seeds. Each seed has a cotyledon, which is stored food that is used by the seed to germinate. A seed which has one cotyledon is called a monocotyledon. A seed with a pair of cotyledons is called a dicotyledon (Figure 1.5).
Paddy plant
Orchid plant
Lotus plant
Sunflower plant
Photograph 1.15 Examples of flowering plants Differences Dicotyledons
Monocotyledons
Number of cotyledons
One
Two
Fibrous root
Root
Tap root
Leaves with parallel veins
Leaf
Leaves with network-like veins
Most have non-woody stem
Stem
Woody stem
Example
Paddy and maize plants
Parallel veins
Tomato plant and durian tree
Network-like veins
Tap root
Fibrous root
Figure 1.5 Differences between monocotyledons and dicotyledons 13
A ctivity 1.2 Aim: To identify the characteristics which differentiate major taxonomy groups. Instruction 1. Work in groups. 2. Identify the differences between (a) plants, animals and fungi (b) fish, amphibians, reptiles, birds and mammals 3. Present the results using a multimedia presentation.
Constructing a Dichotomous Key A dichotomous key is a method used by biologists to identify and classify organisms systematically based on similarities and differences. It is constructed of a series of couplets. Each couplet consist of two statements describing characteristics of a particular organism or group of organisms. Let’s look at the example of a dichotomous key for animals (Figure 1.6) and plants (Figure 1.7).
Pomfret
Chicken
Lion
Frog
Snake
Dichotomous key 1. (a) Poikilothermic ............................................................................... go to 2 (b) Homeothermic ............................................................................. go to 3 2. (a) Scaly skin .................................................................................... go to 4 (b) Non-scaly skin ............................................................................. Frog 3. (a) Non-feathered ............................................................................. Lion (b) Feathered ................................................................................... Chicken 4. (a) Does not have fins ...................................................................... Snake (b) Has fins ....................................................................................... Pomfret
Figure 1.6 Example of a dichotomous key for animals 14
Chapter 1 : Biodiversity
Maize plant
Marchantia sp.
Fern
Gnetum sp.
Sunflower plant
Dichotomous key 1. (a) Non-flowering ............................................................................ go to 2 (b) Flowering .................................................................................. go to 3 2. (a) Non-vascular ............................................................................. Marchantia sp. (b) Vascular .................................................................................... go to 4 3. (a) Monocotyledon .......................................................................... Maize plant (b) Dicotyledon ................................................................................ Sunflower plant 4. (a) Does not produce seeds ............................................................ Fern (b) Produce seeds ........................................................................... Gnetum sp. Figure 1.7 Example of a dichotomous key for plants
A ctivity 1.3 Aim: To construct a dichotomous key. Instruction 1. Work in groups. 2. List down as many invertebrates found in your school compound. 3. Construct a dichotomous key for the invertebrates. 4. Present your group findings in class.
Formative Practice
1.2
1. Classify the following animals according to their common characteristics.
2. The sunflower plant and paddy plant are flowering plants. State one similarity and three differences between the two plants. 3. Give two differences between monocotyledon and dicotyledon plants.
15
16
Without segmented body
Education
Raw material
Medicine
Recreational place
Balance in nature
Food source
Importance
Meaning
Summary
With segmented body
Fern
Flowering
Dichotomous key
Quiz
Interactive Quiz 1
Dicotyledon
Monocotyledon
Plants
using
Conifer
Non-Flowering
Classification
Mammals Birds
Reptiles
Moss
Vertebrates
Animals
Amphibians More than three pairs of legs
With legs
Three pairs of legs
Without legs
Fish
Ways of preserving and conserving biodiversity
Invertebrates
Effects of human activities on biodiversity
Management
Biodiversity
Chapter 1 : Biodiversity
SELF-REFLECTION After learning this chapter, you are able to: 1.1 Diversity of Organisms Elaborate and communicate on biodiversity. Justify the needs of effective biodiversity management. 1.2 Classification of Organisms Differentiate organisms using a dichotomous key based on common characteristics. Characterise the major taxonomy groups.
Summative
Practice
1
1. Complete the crossword puzzle below with the correct answers. (e)
T
(c)
L (d)
I
(a)
I
T
(f) (b)
G
E
A
Across (a) The diversity of organisms whether animals, plants or microorganisms is known as . (b) Amphibians are or cold-blooded. (c) A key is used by biologists to identify and classify organisms systematically.
Down (d) are animals which have backbones. (e) Fish breathe through . (f ) An is an example of a reptile.
17
2. Tick (3) the true statement and cross (✗) the false statement. (a) Biodiversity is the diversity of living and non-living organisms. (b) Biodiversity is very important for the continuity of human’s existence. (c) Apart from classifying living things, a dichotomous key can also be used to classify non-living things. 3. Liana and some of her friends collected the following five types of animals when they conducted a sampling activity in a forest.
Three pairs of legs
Three pairs of legs
Three pairs of legs
Four pairs of legs
More than four pairs of legs
P
Q
R
S
T
(a) Complete the following dichotomous key based on the physical characteristics of the animals collected by them. Five animals: P, Q, R, S, T
(iv)
Three pairs of legs
(i)
With wings
Ant (P)
(ii)
Thin and fragile wings
Ladybird (R)
Body with two segments
Spider (S)
(iii)
(b) What are the similarities between animals P, Q, R, S and T ? (c) What are the differences between animals P, S and T ?
18
(v)
Centipede (T)
Chapter 1 : Biodiversity
4. Observe Figure 1. (a) Suggest two characteristics that can be used to classify plants. (b) Give three similarities between plant A and plant B.
Plant A
Plant B Figure 1
5. Sik Mei observed similarities between the three animals in Photograph 1. Sik Mei thinks that the three animals are in the same group. Is Sik Mei correct? Give your reasons.
Scorpion
Jellyfish
Crab
Photograph 1
6. List the differences between the animals in Photograph 2. Construct a dichotomous key to identify the animals.
Planaria
Butterfly
Earthworm
Photograph 2
HOTS
Mastery
1
7. Deforestation is a huge threat on a global level. Nevertheless, it contributes to the development of a nation. Justify the needs for deforestation. 8. Photograph 3 shows a leatherback turtle, an endemic animal. Hunting this animal has serious consequences. Justify.
Photograph 3
19
Cha
er t p
2
Ecosystem
How does energy flow in an ecosystem? What kind of interaction exists between living things? How is the knowledge on interaction between living things applied in agriculture?
Let’s understand: Energy flow in an ecosystem Nutrient cycle in an ecosystem Interdependence and interaction among organisms, and between organisms and the environment Role of human in maintaining a balanced nature
20
Chapter 2 : Ecosystem
Science Blog
SCIENCE BLOG Programme to Control Monkey Population The Department of Wildlife and National Parks (PERHILITAN) carried out a programme to control the monkey population in Taman Tasik Perdana in the year 2010. This programme was an alternative method to solve the conflict between humans and monkeys. The method used in this programme was sterilisation. It was performed on male monkeys. Then, these sterilised monkeys were released into their original habitat. The monkey population growth rate was studied to observe the effectiveness of this programme.
Keywords Ecosystem
Population
Producer
Community
Consumer
Mutualism
Decomposer
Commensalism
Food chain
Parasitism
Food web
Saprophytism
Species
21
2.1
Energy Flow in an Ecosystem
D
o you know that the source of energy in all ecosystems originates from the Sun? Green plants convert light energy from the Sun into chemical energy through the process of photosynthesis. The chemical energy is transferred to primary consumers and then to secondary and tertiary consumers in the food chain and food web.
Producers, Consumers and Decomposers
In an ecosystem, organisms can be classified as producers, consumers and decomposers.
Producer A producer is an organism that produces its own food through photosynthesis. Most plants are producers.
Primary consumer A consumer is an organism that eats another organism. Primary consumers are herbivores and omnivores that eat producers. For example, caterpillars.
Caterpillar
Plant
Dead
Brain
Teaser
What are the materials that cannot be broken down by a decomposer?
Decomposer A decomposer is an organism that breaks down dead animals and plants into simpler materials or nutrients. This interaction is known as saprophytism.
Figure 2.1 Examples of producer, consumer and decomposer in a forest ecosystem 22
2.1.1
Chapter 2 : Ecosystem
Secondary consumer A secondary consumer is an omnivore and carnivore that eats the primary consumer. For example, the Himalayan bluetail, Tarsiger rufilatus, is an omnivore because it eats caterpillars and fruits. However, the kingfisher, Alcedo atthis, is a primary carnivore because it eats primary consumers such as snails, fish, tadpoles and shrimps.
Brain
Are human beings primary, secondary or tertiary consumers? Explain.
Info
Himalayan bluetail
Teaser
Construct Food Chains http://www.vtaide.com/png/ foodchains.htm#create
SCAN IMAGE
Let’s play
Tertiary consumer A tertiary consumer is a secondary carnivore that eats a secondary consumer. The size of a tertiary consumer is usually bigger than a primary or secondary consumer.
Fox
Science Mushroom
Some examples of decomposers are mushrooms that grow on decaying wood, mould that grows on food as well as E.coli bacteria that break down food molecules in the large intestine of humans.
23
Food Chain A food chain can be used to show the feeding relationship between organisms. Figure 2.2 shows an example of a food chain. Cabbage (Producer)
Snail (Primary consumer)
Bird (Secondary consumer)
Fox (Tertiary consumer)
Figure 2.2 Example of a food chain
Food Web
The interconnection of a few food chains is called a food web. Figure 2.3 shows an example of a simple food web in a vegetable garden. Can you write four food chains that create the food web shown? Energy flow
Caterpillar Bird Snail
Cabbage
Snake Frog
Grasshopper
Figure 2.3 Example of a food web
Energy Flow in a Food Web As seen in the food chain, energy is also transferred from one organism to another organism in the food web. In reality, some of the energy is lost because it is used by the organism to move and carry out the life process of respiration. Apart from this, energy is also lost in the form of heat energy or chemical energy through undigested food, or faeces. Caterpillar
Bird Snake
Snail
Cabbage
Grasshopper
Frog
Energy flow Energy loss
Figure 2.4 Energy flow in a food web
A ctivity 2.1 Aim: To construct a food web. Instruction 1. Visit any ecosystem in your school compound or your housing area. 2. Construct as many food chains as possible from the plants and animals you find. 3. Interconnect the food chains to make a food web. Then, identify the producers, consumers and decomposers in the food web. 4. Discuss the energy flow in the food web. 24
2.1.2
Chapter 2 : Ecosystem
2.1
Formative Practice
1. The following is an example of a food chain. Identify the producer, primary consumer, secondary consumer and tertiary consumer. Cabbage
Caterpillar
Chicken
Snake
2. Based on the following organisms: Paddy plant
Grasshopper
Sparrow
Owl
Rat
Caterpillar
(a) construct a food web. (b) predict what will happen if the paddy plant dies because of a long drought.
2.2
Nutrient Cycle in an Ecosystem
T
he transfer of nutrients and energy is continuous in an ecosystem. Nutrients are obtained from a balanced ecosystem and used by living things. Then, the nutrients are returned to the environment to be used again. This cycle is called a nutrient cycle. Do you still remember the examples of nutrient cycles, such as the water cycle, carbon cycle and oxygen cycle that you learned in Form One? What is the role of living things in those cycles? Water Cycle
Condensation forms cloud
Rain
Respiration, defecation and excretion Transpiration
Surface runoff Evaporation Water seeps underground
Water is absorbed by roots of plants
The role of living things in the water cycle • Water is absorbed by roots of plants in the ground and released into the atmosphere through transpiration. Animals carry out respiration, defecation and excretion (sweating and urination). All of these increase the water content in the atmosphere. • Roots of plants hold the soil tightly and make the structure of the soil more compact. This slows down the flow of water underground and prevents soil erosion. • Leaves that fall from trees and cover the surface of the earth will reduce the rate of evaporation and prevent the soil from becoming dry.
Groundwater storage
Figure 2.5 Water cycle 2.2.1 2.2.2
25
Carbon Cycle and Oxygen Cycle
4
2
Respiration by plants consumes oxygen
Release of carbon dioxide Use oxygen
Oxygen in the atmosphere Plants carry out photosynthesis and release oxygen
1
Release oxygen
Respiration by animals consumes oxygen
Carbon dioxide in the atmosphere Animal respiration releases carbon dioxide
Plant respiration releases carbon dioxide
Plants are eaten by animals. Carbon is stored in the body tissues
Decomposition releases carbon dioxide
Plants die
Animals die Decomposition
Decomposition
Decomposers (Bacteria and fungi)
3
Decay by decomposers consumes oxygen
Figure 2.6 Carbon and oxygen cycles are inter-connected
The role of living things in the carbon cycle and oxygen cycle 1 2 Plants and animals carry out respiration which uses oxygen and releases carbon dioxide. 3 The decay of dead plants and animals by bacteria and fungi in the soil uses oxygen and releases carbon dioxide. 4 Green plants maintain the content of carbon dioxide and oxygen in the air through photosynthesis which absorbs carbon dioxide and releases oxygen.
A
ctivity 2.2
21
st
Century
Aim: To create a multimedia presentation that connects the role of living things in the water cycle, oxygen cycle and carbon cycle. Instruction 1. Work in groups. 2. Design a water cycle, a carbon cycle and an oxygen cycle using multimedia. 3. Predict the effects to the nutrient cycle if the water cycle, oxygen cycle or carbon cycle are affected. 4. Present the multimedia presentation in class.
26
Chapter 2 : Ecosystem
Steps to Solve Problems when there is an Interference to the Nutrient Cycle You have learned the role of plants in maintaining the balance of oxygen and carbon dioxide in the atmosphere. Nevertheless, human activities such as unrestricted logging, burning of fossil fuels and overconsumption of water resources for agricultural and domestic purposes have negatively affected the nutrient cycle. Can you think of steps to solve these problems?
Unrestricted logging
Burning of fossil fuels
Overconsumption of water resources
Create planned agricultural systems
Use public transport
Store rain water for daily use
Replant trees
Tighten laws
Photograph 2.1 Human activities that disrupt the nutrient cycle and steps to solve the problem
Formative Practice 1. 2. 3. 4.
2.2
Name three types of nutrient cycles. Give two processes that change the state of matter in the water cycle. Explain the role of organisms in the carbon cycle and oxygen cycle. Suggest two steps to save water. 27
2.2.3
2.3
Interdependence and Interaction among Organisms, and between Organisms and the Environment
B
efore we study the interdependence and interaction among organisms, and between organisms and the environment, let us understand a few important terms first.
1 Habitat A habitat is the natural surroundings or home of an organism. 2 Species A species is a group of organisms that have common characteristics and can reproduce to breed offsprings.
3 Population A population is a group of organisms of the same species that live in the same habitat.
4 Community A community is a few populations of different organisms that live together in one habitat and have mutual interaction with one another.
Dragonfly Species
A population of dragon flies
5 Ecosystem An ecosystem is a few communities that live together in one habitat and have mutual interaction with one another, including all the non-living components such as water, air and soil.
Pond community
Dragonfly Water hyacinth Grass
Mosquito larvae Fish Water snail
Tadpole
Figure 2.7 Pond ecosystem 28
2.3.1
Chapter 2 : Ecosystem
A Balanced Ecosystem Organisms in an ecosystem are interdependent on each other to ensure the survival of the species. These organisms are also interdependent on non-living components in the environment such as water, light, air and soil. The interdependence that exists between organisms and their natural surroundings creates a balanced ecosystem. An ecosystem is said to be balanced if the living organisms and non-living components in the environment are in a state of harmony without any external interference. Imagine the state of a forest ecosystem if the trees were cut down. Would this ecosystem still be balanced?
STEM
A ctivity 2.3 Aim: To study the habitats, populations and communities in an ecosystem. Instruction 1. Work in groups. 2. Find a natural ecosystem in your area. 3. Conduct an observation of that ecosystem. 4. Take photos and list the species, populations and communities of animals and plants that can be found in that ecosystem. 5. Prepare a folio of the information that you have obtained.
STEM A person who is an expert in the study of ecosytems is called an ecologist.
Questions 1. How do different populations obtain food? 2. How do living organisms interact with their surroundings? 3. What are the benefits that exist from the interaction of organisms and their surroundings? 4. Name an organism and predict what will happen if the population of that organism dies.
Brain Most natural ecosystems are balanced if there is no external interference. Are man-made ecosystems such as aquariums also balanced?
Teaser
Can you name a few other man-made ecosystems?
Photograph 2.2 Example of a man-made ecosystem (aquarium) 29
You have already learned that living organisms are interdependent on one another and also on non-living components to create a balanced ecosystem. What is the effect of these non-living components on the distribution of animals and plants? Let us carry out Experiment 2.1.
Experiment 2.1 Aim: To study the influence of temperature, light and humidity on the distribution of organisms. A
The effect of temperature on the distribution of organisms
Problem statement: What is the effect of temperature on the distribution of woodlice? Hypothesis: Woodlice are more likely to gather in a place with medium temperature. Variables: (a) Constant variables: The number of woodlice, light and humidity (b) Manipulated variable: Temperature (c) Responding variable: Distribution of woodlice Materials: Woodlice, hot water and room temperature water (26°C – 30°C) Apparatus: Petri dish with partition, Petri dish lid, wire gauze, pliers and stopwatch Procedure: 1. Pour 20 ml of hot water (50°C) into partition P of a Petri dish and 20 ml of room temperature water Hot water Water (26°C – 30°C) into partition Q of the same Petri dish. (26°C – 30°C) (50°C) 2. Use a pair of pliers to make a wire gauze mould. Wire gauze mould Petri dish 3. Place the wire gauze mould on the Petri dish. Woodlice lid 4. Put 10 woodlice on the wire gauze above the Petri dish and cover with the lid (Figure 2.8). 5. Leave the apparatus in an open area in the laboratory for five minutes. Partition P Partition Q 6. Record the number of woodlice found in each partition. Conclusion: Is the hypothesis accepted? Give your reasons. B
Figure 2.8
The effect of light on the distribution of organisms
Problem statement: What is the effect of light on the distribution of woodlice? Hypothesis: Woodlice are more likely to gather in a dark place. Variables: (a) Constant variables: The number of woodlice, room temperature and humidity (b) Manipulated variable: Light (c) Responding variable: Distribution of woodlice
30
Chapter 2 : Ecosystem
Material: Woodlice Apparatus: Petri dish with partition, wire gauze mould, Petri dish lid, black cloth and stopwatch
Wire gauze mould Black cloth
Woodlice
Procedure: 1. Pour 20 ml of room temperature water into partition R and S of a Petri dish with partition. Partition R Partition S 2. Use the wire gauze mould made in Experiment A. Water (26°C – 30°C) 3. Place the wire gauze mould on the Petri dish. 4. Put 10 woodlice on the wire gauze mould. Figure 2.9 5. Cover the Petri dish lid of partition R with a black cloth (Figure 2.9). 6. Leave the apparatus in an open area in the laboratory for five minutes. 7. Record the number of woodlice found in each partition.
Petri dish lid
Conclusion: Is the hypothesis accepted? Give your reasons. C
The effect of humidity on the distribution of organisms
Problem statement: What is the effect of humidity on the distribution of woodlice? Hypothesis: Woodlice are more likely to gather in a damp place. Variables: (a) Constant variables: The number of woodlice, room temperature and light (b) Manipulated variable: Humidity (c) Responding variable: Distribution of woodlice Material: Woodlice Apparatus: Petri dish with partition, wire gauze mould, Petri dish lid, anhydrous calcium chloride and stopwatch
Wire gauze mould Water Woodlice (26°C – 30°C)
Procedure 1. Pour 20 ml of room temperature water (26°C – 30°C) into partition T of a Petri dish. 2. Place anhydrous calcium chloride into partition U of Partition T Partition U the same Petri dish. 3. Place the wire gauze mould on the Petri dish. Figure 2.10 4. Put 10 woodlice on the wire gauze mould. 5. Cover the Petri dish with the lid (Figure 2.10). 6. Leave the apparatus in an open area in the laboratory for five minutes. 7. Record the number of woodlice found in each partition.
Petri dish lid Anhydrous calcium chloride
Conclusion: Is the hypothesis accepted? Give your reasons.
31
Importance of Adaptation of Living Things to the Environment Tropical areas receive high distribution of rainfall and sunlight throughout the year. Desert areas experience extreme hot and dry weather. Tundra areas experience long winters and short summers. How does wildlife adapt to the climate of their habitat in tropical, desert and tundra areas?
Desert
Tropical
Tundra Photograph 2.3 Tropical, desert and tundra areas
A
ctivity 2.4
21
st
Century
Aim: To carry out multimedia presentation on how animals and plants adapt to the climate of their habitats; in desert, tundra and tropics. Instruction 1. Work in groups. 2. Each group represents one of the three different areas of habitats; desert, tundra and tropics. 3. Collect materials from a variety of media about the habitat. 4. Discuss the adaptation of animals and plants to the climate in their habitats. 5. Present your results using a multimedia presentation.
32
2.3.2
Chapter 2 : Ecosystem
Interaction between Organisms Interaction between organisms comprises symbiosis, prey-predator and competition. Types of interaction between organisms Symbiosis Mutualism
Prey-predator
Commensalism
Competition
Parasitism Video
Video of Interaction between Organisms and Their Surroundings http://www.bukutekskssm.my/ Science/Video1.mp4
Figure 2.11 Types of interaction between organisms
Symbiosis Symbiosis happens when two or more organisms of different species live closely together and interact with one another. Symbiosis includes mutualism, commensalism and parasitism. Mutualism • An interaction that benefits both organisms. Photograph 2.4 shows a few examples of mutualism. Fungi
Algae
• The sea anemone protects the clown fish from predators and supplies food to it. • The clown fish cleans the sea anemone and provides nutrients to the sea anemone in the form of waste.
Mynah
Buffalo
Lichens are algae and fungi that live together. • The fungi supply water and minerals to the algae. • The algae carry out photosynthesis and supply food to the fungi. • The mynah gets food from the buffalo by eating the lice that stick to the body of the buffalo. • The body of the buffalo is free of lice.
Photograph 2.4 Examples of mutualism 2.3.3
33
Commensalism • The interaction between two organisms which only benefits one organism without harming or benefitting the other. • Commensal is the organism that benefits.
The remora fish (commensal) latches on the shark (host) and gets its food from scraps scattered by its host.
Shark Remora fish
Bird’s nest fern
The bird’s nest fern (commensal) grow in between the branches of trees (host) to get sunlight.
Photograph 2.5 Examples of commensalism
Parasitism • An interaction that benefits one organism only and harms the other. • Parasite is the organism that benefits. • Host is the organism that is harmed.
The tapeworm (parasite) that lives in the human intestine (host) absorbs nutrients. Tapeworm
Lice (parasite) suck the blood of humans and animals (host). Lice Photograph 2.6 Examples of parasitism 34
Chapter 2 : Ecosystem
Prey-predator • Involves one organism that eats another organism. • Prey is the organism that is eaten by the predator. • Predator is the organism that hunts another organism for food.
Predator
Predator
Prey
Prey Photograph 2.7 Examples of prey-predator
Competition • Competition happens when organisms in one habitat compete for limited supply of basic needs such as light, space, water, food and mates.
Competition to get food
Competition to get mate to reproduce
Photograph 2.8 Examples of competition 35
Biological Control Biological control is a method that uses organisms that are natural predators, parasites or pathogens to reduce the number of pests in an area. Photograph 2.9 shows examples of biological control that are used in the agricultural sector in Malaysia. Owls are kept in palm oil plantations to control the population of rats. Rhinoceros beetle
Bacillus thuringiensis is used to control pests, namely the rhinoceros beetle in palm oil plantations.
The guppy is a predator to mosquito larvae in a pond. Guppy Mosquito larvae
The ladybird beetle eats aphids, a crop pest.
Ducks are reared in paddy fields to eat pests such as snails and insects.
Photograph 2.9 Examples of biological control in Malaysia
Biological control is more environmental friendly because it does not use pesticides or chemicals. Apart from this, this method is usually cheaper and does not affect humans’ health. Nevertheless, this method has a few weaknesses such as: • it takes a long time before any effect is seen. • the balance of the ecosystem might be disrupted because a new species is introduced into that ecosystem. 36
Chapter 2 : Ecosystem
Factors that Influence Population Size in an Ecosystem How does population size change in an ecosystem? Among the factors that cause population size to change is disease, the presence of predators, source of food and change of weather. Disease The population of animals and plants decreases when a disease strikes. For example, avian flu in poultry-rearing areas and tobacco mosaic virus in tobacco crops.
Presence of predators
Photograph 2.10 Poultry affected by a disease
The population size of a living organism is influenced by the population size of its predator. For example, the size of the zebra population in the savanna ecosystem decreases with the presence of its predators such as the lion.
Photograph 2.11 Tobacco crops struck by a disease
Photograph 2.12 Zebra being eaten by a lion
Source of food If a food source decreases, animals can be threatened by extinction. For example, panda depends on bamboo as its primary food source. Clearing of forests has caused the destruction of its food source and habitat. In Malaysia, the crow population has increased due to the abundance of food scraps.
Photograph 2.13 Panda Photograph 2.14 Crow
Change of weather
Droughts cause soil to become dry and infertile and increase the risk of forest fires. As a result, the population of plants and animals decreases. Photograph 2.15 Soil becomes dry and infertile Photograph 2.16 Forest fires resulting from a long drought
2.3.4
37
Changes in the Ecosystem Changes in the ecosystem such as limited water supply, animal migration and decrease or increase in population size can upset the balance between populations. Limited water supply • Paddy is a plant that requires a lot of water. • If there is a long drought season, this change in the ecosystem will upset the balance between populations in the paddy field. • The food web will be affected because the population of the producer, which is paddy, decreases.
Migration
Photograph 2.17 Insufficient water supply disrupts the ecosystem of a paddy field
• The ecosystem can also change because of animal migration, moving from one place to another due to a change of season. • For example, the cattle egret (Bubulcus ibis) migrates to Kuala Gula, Perak from September to April every year. As a result, the number of insects such as grasshoppers, crickets, spiders, flies and worms decreases as they are eaten by the egrets.
Photograph 2.18 Cattle egret which migrates to Kuala Gula, Perak
Change in population size • The size of a population can decrease or increase because of changes in another population. • For example, the increase of pests such as beetles and caterpillars causes the population of plants to decrease.
Science
Photograph 2.19 Overpopulation of beetles destroys crops 38
In 2015, the southern region of Russia was attacked by locusts which destroyed crops. Cornfields as wide as 800 hectares were destroyed in just a few hours.
2.3.5
Chapter 2 : Ecosystem
Formative Practice
2.3
1. Fill in the boxes using the choice of answers given.
(a) A group of goats in a grass field. (b) A small pond that has lotus plants, grass, a group of tadpoles, a few fish, ducks and frogs. (c) A grass field that becomes the living place of a group of goats. (d) A tropical rainforest where there are a variety of plants and animals that are interdependent on one another. 2. Based on the situation below, state the kind of interaction that happens between these living organisms. Situation
Type of interaction
(a) Two roosters fight to get a mate to reproduce (b) A cucumber plant wraps around the branch of a papaya tree (c) A rafflesia flower grows on the branch of a live tree
2.4
N
Role of Humans in Maintaining a Balanced Nature
ature is threatened by destruction because of human activities. As such, humans are responsible for conserving and maintaining the balance of nature. Table 2.1 Effects of human activities on the environment Activity
Effects
Forest logging
• Extinction of flora and fauna species • Greenhouse effect
• Soil erosion
Industrialisation
• Pollution of air, water and soil • Greenhouse effect
• Acid rain
Agriculture
• Pollution of water due to overuse of pesticides and fertilisers • Soil loses minerals due to non-sustainable agriculture
Waste disposal
• Pollution of water and ground • Flash floods
• Foul odour due to decaying organic waste matter
Steps to solve the effects of human activities on the environment • Enforce laws The Forestry Department is always conducting law enforcement activities in all states. For example, carrying out patrols in the forest area, using helicopters and having road blocks to monitor the movement of timber-carrying lorries. 2.4.1
39
• Increase public awareness In schools, students are instilled with good values through Moral Education to appreciate the balance of nature. These good values are also instilled through mass media such as newspapers, radio and television. • Practise Refuse, Reduce, Reuse, Recycle, Repurpose (5R) The practice of refuse (not to use non-recyclable materials), reduce (reduce the number of materials to use), reuse (reuse the materials), recycle (recycle materials) and repurpose (use the materials for other uses) can reduce the waste materials. • Use biological control Avoid the use of pesticides that pollute the air and soil by carrying out biological control in agriculture.
STEM
A ctivity 2.5
21
st
Century
Aim: To carry out a role play to discuss the importance of humans to manage and ensure the sustainability of life. STEM Instruction 1. Work in groups. An environmental consultant cares for the environment 2. Each group has to choose one of the following from a science and environmental issues in Malaysia: technology aspect to make it (a) waste management system sustainable. (b) flood dam project (c) forest management (d) haze 3. Identify several agencies or stakeholders and public to solve the selected environmental issue. 4. Organise a forum to discuss: (a) the cause of the environmental issue (b) the effect of the evironmental issue on the local community (c) solutions for the issue 5. Each group member must represent the roles of agencies, stakeholders and the public in the forum.
Formative Practice
2.4
1. List four human activities that can destroy the ecosystem. 2. State two effects for each of the following activities to the balance of nature. (a) Deforestation (c) Agriculture (b) Industrialisation (d) Waste disposal 3. Mr. Lim wants to start a sustainable oil palm plantation. In your opinion, how can Mr. Lim control the rat population that frequently destroys crops? 4. Haze happens more frequently in our country. State: (a) the cause of haze (b) the effects of haze on people and the environment (c) the steps to be taken to avoid haze from happening 5. Give two reasons why humans need a balanced ecosystem. 40
Mutualism
Commensalism
Symbiosis
• Disease • Predator • Food source • Weather
Parasitism used in
Prey-predator used in
interact with one another
Organisms
Factors that influence
Types of interaction
Summary
Biological control
Competition
change of size
Humans’ role
requires
Balanced ecosystem
interdependent
Quiz
Oxygen cycle
Interactive Quiz 2
Carbon cycle
Water cycle
Nutrient cycle
has
Environment
Tertiary consumer (Secondary carnivore)
Secondary consumer (Primary carnivore)
Community Ecosystem
Primary consumer
Producer
Population
Species
Chapter 2 : Ecosystem
41
SELF-REFLECTION After learning this chapter, you are able to: 2.1 Energy Flow in an Ecosystem Explain through examples; producer, consumer and decomposer. Interpreting food chains and food webs. 2.2 Nutrient Cycle in an Ecosystem Elaborate and communicate the role of living things in oxygen and carbon cycles in an ecosystem. Justify the role of organisms in water cycle in an ecosystem. Solve problems when there is an interference to the cycles due to human activities. 2.3 Interdependence and Interaction among Organisms, and between Organisms and the Environment Explain through examples interdependence among living things and the environment in maintaining a balanced ecosystem. Justify the importance of adaptation of living things to the environment. Communicate through examples the interaction between organisms and apply these interactions in daily life. Separate the factors that affect the size of population in an ecosystem. Predict how the changes in ecosystem affect resources and balance of population. 2.4 Role of Humans in Maintaining a Balanced Nature Justify and communicate why humans need a stable and productive ecosystem for the sustainability of life.
Summative
Practice
2
1. Based on the food web in Figure 1, answer the following questions. Fox Rabbit
Grass
Rat Sapling Figure 1
42
Chapter 2 : Ecosystem
(a) Construct all the food chains from the food web in Figure 1. (b) Why is grass categorised as a producer? (c) If a flea lives on the body of a rabbit and sucks its blood, what type of interaction occurs between the flea and the rabbit? (d) Predict what will happen if the population of fox in that area caught a disease. 2. City X is well-known as a rat-breeding area. (a) State the effects of the high rat population on the inhabitants of City X. (b) In your opinion, what is the cause of the high rat population in City X? (c) Suggest two steps to solve the issue of rat-breeding that can be taken by: (i) the authorities
(ii) the inhabitants
3. Shikin and Azah have different opinions about producers and decomposers. Their opinions are as follows. Shikin : Producers can still live without decomposers because producers can make their own food. Azah : If there are no decomposers, producers cannot get enough nutrients. The producers could die. Give your view on Shikin and Azah’s opinion. 4. Razak found that many of his chickens were eaten by Hawk-Eagles. Razak made a decision to shoot all the eagles. After a year, the rat population increased and ate all the chicken feed. This caused chickens to die. Explain the cause for the increase in the rat population and suggest a way Razak can prevent this from happening.
HOTS
Mastery
2
5. An urban or city forest is an area that is planted with trees all around the city. Justify the idea of a city forest in terms of preserving a balanced ecosystem. 6. Photograph 1 shows a common rat trap sold in stores. This trap can only catch one rat at one time. Design a rat trap model that can catch more than one rat at one time. Sketch and explain your design.
Photograph 1
43
Cha
er t p
3
Nutrition
What kind of food gives us energy? How do the energy needs of one individual differ from another individual? What happens to the food that we eat?
Let’s understand: Classes of food Importance of a balanced diet Human digestive system Process of absorption and transportation of digested food and defecation 44
Chapter 3 : Nutrition
Science Blog
SCIENCE BLOG Astronaut Food Malaysia’s first astronaut, Dato’ Dr. Sheikh Muszaphar Shukor was flown to the International Space Station (ISS) on 10th October 2007. In relation to that, Malaysian Agricultural Research and Development Institute (MARDI) was tasked with carrying out a research about food for astronauts while they were in space. According to the research carried out, the salt content in food decreases in space. Therefore, the research was done numerous times until it produced appetising, delicious and nutritious food in space. Then, the food produced was sent to Russia to undergo various tests before getting approval. The food prepared was stored in air-tight plastic containers and was frozen to avoid spoilage.
Kata Kunci Keywords Carbohydrate
Absorption
Protein
Oesophagus
Fat
Small intestine
Vitamin
Large intestine
Mineral
Rectum
Fibre
Anus
Balanced diet
Defecation
Digestion
45
3.1
W
Classes of Food hat is your daily diet? Is it nutritious and energy-giving? Food not only supplies energy but also gives nutrients to maintain our health.
Nasi lemak
Satay
Photograph 3.1 Food is a basic need for humans
Our food is divided into seven main classes; carbohydrate, protein, fat, vitamin, mineral, fibre and water (Figure 3.1). Each food class has a specific function. Can you identify the food classes that are shown in each food item in Photograph 3.1? Classes of food
Carbohydrate
Protein
Fat
Vitamin
Mineral
Fibre
Water
Figure 3.1 Classes of food
Carbohydrate Carbohydrate is an organic compound that contains carbon, hydrogen and oxygen. Carbohydrate is a staple for humans because it supplies a lot of energy. Examples of carbohydrate are starch, glycogen and cellulose. Starch is the food stored in plants, whereas glycogen is the food stored in animals. Cellulose is the carbohydrate that forms the cell walls of plants.
46
Science Some sources of carbohydrate, such as sugar supply energy quickly.
3.1.1
Chapter 3 : Nutrition
Banana
Rice
Bread
Potato
Honey
Sugar
Photograph 3.2 Sources of carbohydrate
Science
Protein Protein is a food substance that contains carbon, hydrogen, oxygen and nitrogen. Proteins we eat are digested to the basic unit, that is, amino acid. Protein is required for growth and to repair damaged tissues in the body as well as to replace dead cells. Apart from that, protein is also used to synthesise enzymes, hormones and antibodies. Photograph 3.3 shows a few sources of protein.
Kwashiorkor is a kind of disease caused by protein deficiency in human diet and it generally occurs in children aged between 1 and 3 years.
Chicken
Seafood Nuts
Milk helps me to grow because it is high in protein. Meat
Egg
Photograph 3.3 Sources of protein 47
Science
Fat As in carbohydrate, fat contains carbon, hydrogen and oxygen. Fat is formed from glycerol and fatty acid. Fat is a high energy source and storage. Each gramme of fat supplies two times the total energy supplied by carbohydrates. Fat protects the organs of the body such as the heart and kidneys. Apart from that, fat acts as a transporter for vitamin A, D, E and K. Excess fat in the body is stored under the skin as a heat insulator to regulate body temperature.
Fat from animals contains higher cholesterol than fat from plants.
Groundnuts
Butter
Coconut oil
Palm oil
Photograph 3.4 Sources of fat
Vitamin Vitamin is an organic compound that does not supply energy, but is needed by the body in small quantities to maintain good health. Vitamins can be classified as water-soluble vitamins and fat-soluble vitamins (Figure 3.2). We obtain vitamins from vegetables, fruits, milk and meat. Table 3.1 shows the types, sources, importance and effects of vitamin deficiency. Vitamins
Water-soluble vitamins
Fat-soluble vitamins
Vitamin B and C
Vitamin A, D, E and K
Figure 3.2 Classification of vitamins
Milk
Meat
Fruits
Photograph 3.5 Sources of vitamins 48
Vegetables
Chapter 3 : Nutrition Table 3.1 Type, source, importance and effects of vitamin deficiency Vitamin
Source
Importance
Effects of deficiency
A
milk, egg yolk, fish oil
• Helps with night vision • Maintains skin health
• night blindness • skin diseases
B
yeast, liver, eggs
• Maintains the functions of the nervous system • Formation of red blood cells
• Beri-beri • Anaemia
C
fruits, vegetables
• Fights diseases • Maintains the health of gums and mouth
• Scurvy (bleeding gums)
D
butter, eggs, fish oil, also produced through sun exposure
• Helps in the absorption of calcium • Strengthens tooth enamel • Maintains skin health
• Rickets • toothache • skin diseases
E
grains, green vegetables
• Maintains the functions of reproductive system
• sterility • foetus miscarriage
K
milk, egg yolk, fish oil
• Speeds up the blood-clotting process
• prolonged bleeding
Fibre Fibre is a substance that cannot be broken down by the digestive system. Fibre comprises of cellulose that is found in the cell wall of plants. Fibre is very important to stimulate peristalsis, that is, the movement caused by the constriction and relaxation of the muscles along the digestive tract such as oesophagus, small intestine and large intestine. This makes it easier for food to move along the digestive tract and prevents constipation.
Fruits, vegetables and grains are high in fibre.
High fibre bread
Vegetables
Grains
Photograph 3.6 Sources of fibre
49
Mineral Mineral is a non-organic substance required by the body. Minerals do not supply energy, but are required in small quantities to regulate body processes to maintain health. Table 3.2 shows a variety of minerals, their importance and effects of deficiency.
Salt
Seafood
Photograph 3.7 Sources of mineral Table 3.2 Types, sources, importance and effects of mineral deficiency Mineral
Source
Importance
Effects of deficiency
Calcium
milk, anchovies, prawns, green vegetables
• Helps with blood-clotting • Strengthens bones and teeth
• Rickets • Osteoporosis
Sodium
salt, meat, eggs
• Maintains the functions of the nervous system
• muscle cramps
Iron
liver, meat
• Builds haemoglobin in the blood
• Anaemia
Iodine
seafood, fruits
• Helps with the funcions of thyroid gland
• Goiter
Phosphorus
cheese, meat, eggs, vegetables
• Strengthens bones and teeth • Forms nucleic acid in DNA and RNA
• Rickets • brittle teeth • cannot build DNA and RNA
Potassium
plants and animals
• Helps with muscle contraction • Maintains the functions of nervous system
• paralysis • muscle cramps
Water Water is a compound that is very important to our body. Water contains elements of hydrogen and oxygen. Water acts as a chemical solvent and a transportation medium of nutrients and oxygen into the cells. It transports waste materials such as urea and salt out of the cells and regulates body temperature through evaporation of sweat.
Fruit juice
Watermelon
Photograph 3.8 Sources of water
50
We need to drink at least 2 litres of water a day.
Chapter 3 : Nutrition
A ctivity 3.1 Aim: To test for the presence of starch, glucose, protein and fat. Materials: Iodine solution, 1% starch suspension, Benedict's solution, 10% glucose solution, Millon’s reagent, albumen suspension, ethanol, cooking oil and distilled water Apparatus: Test tube, dropper, beaker, Bunsen burner, wire gauze, tripod stand, test tube holder, stopper and test tube rack A
Iodine test for starch Iodine solution
Instruction 1. Pour 2 ml of starch suspension into a test tube. 2. Add two drops of iodine solution into the test tube (Figure 3.3). 3. Record your observations.
B
Figure 3.3
Benedict's test for glucose
Instruction 1. Pour 2 ml of glucose solution into a test tube. 2. Add 2 ml of Benedict's solution into the test tube and shake it to mix the solutions. 3. Heat the test tube in a water bath for 5 minutes (Figure 3.4). 4. Record your observations.
C
2 ml of 1% starch suspension
Water bath
Tripod stand
Bunsen burner
Figure 3.4
Science Benedict's test is used to test the presence of reducing sugars. Examples of reducing sugars are glucose, maltose, galactose and fructose.
Millon's test for protein
Instruction 1. Pour 5 ml of albumen suspension into a test tube. 2. Add two to three drops of Millon's reagent into the test tube (Figure 3.5 (a)). Then, shake the test tube to mix the solutions. 3. Heat the test tube in a water bath for 5 minutes (Figure 3.5 (b)). 4. Record your observations.
Glucose solution + Benedict’s solution
Wire gauze
Water bath Millon’s reagent
Albumen suspension + Millon’s reagent
Wire gauze
Bunsen burner
Albumen suspension (a)
(b) Figure 3.5
3.1.2
51
D
Alcohol-emulsion test for fat
Instruction Cooking 1. Pour 3 ml of ethanol into a test tube. oil 2. Add 2 to 3 drops of cooking oil into the test tube (Figure 3.6 (a)). Then, close the test tube with a stopper. 3. Shake the test tube slowly and leave it in a test tube rack Ethanol for 2 to 3 minutes. 4. Place 4 to 5 drops of the mixture from the test tube into (a) (b) another test tube filled with 20 ml of distilled water Figure 3.6 (Figure 3.6 (b)). Safety 5. Close the test tube with the stopper and shake slowly. Leave Precaution the test tube in the test tube rack for 2 to 3 minutes. Ethanol is flammable. 6. Record your observations.
Ethanol + cooking oil
Distilled water
Please keep it away from fire.
Observation Activity
Observation
A B C D Questions 1. Why is the heating in the Benedict's is test and Millon’s test carried out in a water bath? 2. You are given a food sample in powder form. How do you determine the food class of the food sample? 3. What are the inferences you can make from each of the activity above?
Formative Practice
3.1
1. Name the food class based on the functions given. Food class
Function
(a)
Regulates body temperature
(b)
Heals damaged body tissues
(c)
Required for energy
(d)
Protects from diseases
2. Name the diseases caused by deficiencies of the following vitamins. (a) Vitamin A (c) Vitamin C (b) Vitamin B (d) Vitamin D 3. State the effects to our health caused by deficiencies of the following minerals. (a) Iodine (b) Iron (c) Phosphorus
52
Chapter 3 : Nutrition
3.2
Importance of a Balanced Diet
What is meant by a balanced diet? A balanced diet is a diet that contains all the food classes in the right quantities that are required by the body.
My
World
Mother, how do I prepare a healthy meal?
Science
We can refer to the food pyramid as a guide to prepare a healthy meal.
The “Healthy Plate” model has been prepared by the Ministry of Health Malaysia as a guide to practise a balanced diet.
Info
• FISH, CHICKEN, MEAT AND NUTS 1/2 – 2 servings of chicken/meat/ eggs daily 1 serving of fish daily 1/2 – 1 serving of nuts daily
‘Heathy Plate’ Model http://www.moh. gov.my/index.php/ pages/view/84
• FAT, OIL, SUGAR AND SALT Eat sparingly • MILK AND DAIRY PRODUCTS 1 – 3 servings daily
• FRUITS 2 servings daily
• VEGETABLES 3 servings daily
• RICE, NOODLES, BREAD, GRAINS AND POTATOES 4 – 8 servings daily Source: Ministry of Health Malaysia
Figure 3.7 Food pyramid 3.2.1
53
Factors that Influence Calorific Requirement Body size A person with a large body frame needs to take a bigger portion of food because he or she needs to have more energy compared to someone with a smaller frame.
Age Children and teenagers require more carbohydrates for energy and protein for growth because they are growing and are more active compared to adults.
Work Farmers, labourers and fishermen require more energy because they do heavy work. Therefore, their diet requirements are higher compared to people who work in an office.
Gender Generally, men are more muscular and they do more heavy activities. Therefore, they need bigger food portions than women.
State of health People who are sick are weak. They require food suitable to their health condition.
Climate People who live in cold climate countries lose heat quickly to their surroundings compared to people who live in hot climate countries. Therefore, they need more food to maintain their body temperature.
Figure 3.8 Factors that influence a calorific requirement 54
Chapter 3 : Nutrition
Calorific Value of Food Food contains some basic classes, such as carbohydrate, protein and fat. All of these basic classes produce different quantities of energy when burned. The total amount of energy released when 1 g of food is burned completely in the body is called energy value or calorific value. This total energy is measured in units of calorie (cal) or joule (J). Table 3.3 Energy value of fat, protein and carbohydrate Energy value
Food class
(kJ / g)
(kcal / g)
37 17 17
9 4 4
Fat Protein Carbohydrate
1 calorie (cal) = 4.2 joule (J) 1 kilocalorie (kcal) = 4.2 kilojoule (kJ)
You have learnt about the calorific value of food. Can you estimate the calorific value of the food in your daily meals? Let’s do Activity 3.2.
STEM
A ctivity 3.2 Aim: To estimate the calorific value of food. Instruction 1. List the breakfast menu of your friends in class. Example of a breakfast menu:
2. Estimate the calorific value for each of your classmates’ menu items. You can scan the QR code given to know the calorific value of the food. Example of the calculation: Quantity
Calorific value (kcal)
Fried rice
1 plate (330 g)
640
Banana
2 pieces (120 g)
60 × 2 = 120
Milk
1 glass (250 ml)
130
Food Fried rice
Banana
The total calorific value for the breakfast consumed is 890 kcal Milk
3. Find out whose breakfast has the highest and lowest calorific values.
STEM Calorific Value of Food http://www.moh.gov.my Info
3.2.2
A dietitian gives advice in terms of evaluating the status of an individual’s diet before recommending a suitable diet.
55
How does the knowledge of calorific value of food help you choose food?
Let’s carry out Activity 3.3.
A ctivity 3.3 Aim: To collect information on calorific value of food. Instruction 1. Work in groups. 2. Each group is required to collect 2 food labels that show the food calorific value (Figure 3.9).
NUTRITION FACTS Serving size: 43 g (1/3 can) Amount per serving (43 g) NUTRITION FACTS Serving size: 43 g (1/3 can) Amount per serving (43 g)
Per 100 g
Energy (1 kcal = 4.2 kJ) Protein
48 kcal 10.2 g
111 kcal 23.8 g
Fat Omega 3
0.3 g 155 mg
1.2 g 360 mg
Cholesterol Carbohydrate Fibres
24 mg 0.5 g 1.1 g
57 mg 1.1 g 2.6 g
Sodium
65 mg
152 mg
NO ADDED MSG / NO PRESERVATIVE
Per 100 g
Energy (1 kcal = 4.2 kJ) Protein
48 kcal 10.2 g
111 kcal 23.8 g
Fat Omega 3
0.3 g 155 mg
1.2 g 360 mg
Cholesterol Carbohydrate Fibres
24 mg 0.5 g 1.1 g
57 mg 1.1 g 2.6 g
Sodium
65 mg
152 mg
NO ADDED MSG / NO PRESERVATIVE
Figure 3.9
3. Fill in the calorific value of food found on the food labels in a table like the one below: Food Canned food
Class of Food
Per 100 g
Calorific value (kJ)
Carbohydrate Protein Fat Carbohydrate Protein Fat
4. Discuss the following things: (a) which food has the lowest and highest calorific values? (b) what other nutrients are printed on the food labels apart from carbohydrate, protein and fat?
56
Chapter 3 : Nutrition
Planning a Balanced Diet
Brain
Have you ever planned a balanced diet based on your calorie and nutrient requirements? As we have learnt, factors such as size of body frame, age, work, gender, health condition and climate influence the calorie and nutrient needs of a person.
Teaser
If you are required to plan a menu for astronauts, what food would you recommend?
Why is planning a balanced diet important?
So that we remain active and healthy.
A ctivity 3.4 Aim: To plan a balanced meal for a day based on different factors. Instruction 1. Work in groups. 2. Each group is required to prepare a menu for breakfast, lunch and dinner for one of the following individuals: Individual A: a man who works as a bank officer Individual B: a man who works as a construction worker Individual C: a pregnant woman Individual D: a school girl who is active in sports 3. Determine the quantity required for each food menu. 4. Total the calorific values consumed in one day. 5. Produce the planned menu according to your group’s creativity. Questions 1. What class of food appears the most in the food menus? 2. State the factors that were considered when planning the daily menu. 3. Which individual’s meal has the highest calorific value?
57
The Importance of Maintaining Health According to the research results of the National Health and Morbidity Survey (2016), the percentage of Malaysians with diabetes is 17.5%, high blood pressure is 30%, high cholesterol is 47%, obesity is 17% and overweight is 40%. This problem shows the improper diet and lifestyle of Malaysians. Activities to create awareness should be carried out more actively at school level.
A ctivity 3.5 Aim: To create awareness and emphasise the importance of maintaining a healthy body. Instruction 1. Work in groups. 2. Collect information on: (a) heart diseases (b) high blood pressure (c) diabetes (d) skin cancer (e) lung cancer 3. Prepare a poster about the causes of these diseases and steps that can be taken to prevent them. 4. Put up the three best posters on the science notice board in your class.
We need to practise a healthy lifestyle such as eating food with less sugar, salt, oil and fat. Besides, we need to exercise and should not smoke to maintain our health and to reduce the risk of dangerous diseases. The existence of various high-calorie foods has caused more people to be categorised as obese. Obesity is a problem that not only has a negative effect on the appearance of an individual, but also destroys health without considering age or background.
Science The research results of the National Health and Morbidity Survey 2016 shows that only six percent of Malaysian adults eat enough fruits and vegetables. Thus, the Ministry of Health Malaysia launched the Eat Fruits and Vegetables Campaign.
Photograph 3.9 Balanced diet can maintain health 58
Chapter 3 : Nutrition
Science Body Mass Index (BMI) is a formula that calculates body mass against height. We can evaluate our body mass index after calculating the BMI.
Scan the QR code below for the Classification of Body Mass Index (BMI) for male and female students aged 9 – 17 years.
Calculation of Mass (kg) Body Mass Index = Height (m) × Height (m) (BMI)
Classifying BMI jpnpahang.moe.gov.my Info
A ctivity 3.6 Aim: To study the obesity problem among school children and suggest ways to overcome it. Instruction 1. Conduct a study on the obesity problem among students in your school. 2. You need to study: (a) the relationship between eating processed and junk food and the problem of obesity (b) ways to solve the problem at school level 3. Write the results of your study in the form of a folio.
Formative Practice 1. 2. 3. 4. 5.
3.2
What is meant by a balanced diet? State the factors that influence calorific requirement. Compare the energy requirements of a 50-year-old woman and 50-year-old man. Give the definition for calorific value of food. Suraya is a long-distance runner. She has breakfast as shown in the photographs below before going for a practice session. What is the calorific value of the food consumed by Suraya? In your opinion, has Suraya taken a balanced meal?
A plate of nasi lemak (400 kcal)
A cup of cornflakes (160 kcal) and a cup of milk (130 kcal)
An apple (60 kcal)
6. Mr. Robert originates from Switzerland and now lives in Malaysia. Mr. Robert works as a diplomatic officer. He finds that his daily food requirements are less compared to when he was in Switzerland. Why?
3.2.3
59
3.3
Human Digestive System
W
hat happens in our body after we eat? How is food like the watermelon in Photograph 3.10 digested? Let us learn about the process of food digestion. Photograph 3.10
Science Enzyme is a substance in the body that speeds up chemical digestion.
Happens in the mouth
Break down of food occur
Physical digestion
Does not involve enzymes
Happens in the mouth, stomach, duodenum and intestine Chemical digestion
Happen in the digestive tract
Involves enzymes
Figure 3.10 Comparison between physical digestion and chemical digestion 60
3.3.1
Chapter 3 : Nutrition
The Structure of the Human Digestive System
Brain
If a digestive tract is 9 m long, how does the tract fit into a body that is 1.5 m in height?
What are the organs that are involved in the human digestive system? The human digestive system comprises a tube that is called the digestive tract and a few other organs such as the liver, gall bladder and pancreas. The digestive tract is a long tube that begins in the mouth and ends at the anus.
Mouth
Teaser
Mouth
Salivary glands
Oesophagus
Oesophagus
Stomach
Duodenum
Liver
Stomach
Duodenum
Gall bladder Small intestine
Pancreas
Large intestine
Small intestine Large intestine
Rectum
Rectum
Anus
Anus Figure 3.11 Human digestive system
Figure 3.12 The flow of food particles 61
The Flow of Food in the Digestive Tract What happens when food passes through each organ in the digestive tract?
1 • • •
Mouth Food is chewed by the teeth. Particles of food are softened by saliva. Salivary amylase in saliva breaks down starch into maltose.
1 SCAN IMAGE
Animation of Flow of Food
2 Oesophagus • Food that enters the oesophagus is called bolus. • The process of peristalsis at the wall of the oesophagus pushes the food into the stomach.
2
3 3 Stomach • Walls of the stomach secrete protease and hydrochloric acid. Hydrochloric acid activates the protease and kills bacteria in the food that enters the stomach. • Protease breaks down protein into polypeptides. • Food that is semi-liquid is called chyme.
4
6
5
7 62
8
Chapter 3 : Nutrition
4 Duodenum • Food enters the first part of the small intestine, that is, the duodenum. • The liver produces bile that is stored in the gall bladder. • The bile emulsifies fat into small droplets and neutralises the acid in the chyme. • The pancreas produces pancreatic juice which contain enzymes amylase, protease and lipase. • Pancreatic amylase digests starch into maltose. • Protease digests polypeptides into dipeptides. • Lipase digests fat into fatty acids and glycerol.
5 • • •
Small intestine The small intestine secretes enzymes maltase and protease. Maltase digests maltose into glucose. Protease digests dipeptides into amino acids.
6 Large intestine • Undigested food will enter the large intestine. • The process of water reabsorption happens in the large intestine.
7 Rectum • Food that is undigested, known as faeces, enters the rectum and is stored here.
8 Anus • Faeces are excreted from the body through the anus.
Figure 3.13 Human digestive system 63
Our body produces enzymes to quicken the food digestion. What are the examples of enzymes that are involved in digestion? What is the function of each of these enzymes? Amylase, protease and lipase are examples of enzymes in digestion. Enzymes are made up of protein. Without enzymes, the digestion process happens at a very slow rate.
Starch
1
Maltose
4
Amylase (Secreted by salivary glands and pancreas)
Maltose
2
Glucose
Protein
Polypeptide
Protease (Secreted by the stomach)
Some detergents contain enzymes. These enzymes help to remove stains such as blood and oil.
Polypeptide
Dipeptide
Protease (Secreted by the pancreas)
5
Maltase (Secreted by the small intestine)
3
Science
Dipeptide
Amino acid
Protease (Secreted by the small intestine)
6
Fat
Fatty acid + Glycerol
Lipase (Secreted by the pancreas)
Figure 3.14 Action of digestive enzymes
A ctivity 3.7 Aim: To study the action of enzyme in saliva on starch. Materials: 1% starch suspension, iodine solution, Benedict's solution and distilled water Apparatus: Boiling tube, Bunsen burner, glass rod, wire gauze, 250 ml beaker, test tube, test tube holder, stopwatch, dropper, tripod stand, retort stand with clamp Instruction 1. Rinse your mouth with distilled water and collect saliva in a small beaker. Use this in step 3. 2. Pour 10 ml of starch suspension into two boiling tubes, P and Q. 3. Add 4 ml of the saliva into boiling tube Q. Stir the mixture with a clean glass rod. 4. Take out 2 ml from each of the boiling tubes and carry out iodine test and Benedict's test. 5. Place boiling tubes P and Q in a water bath at 37ºC and start the stopwatch (Figure 3.15). 6. After 30 minutes, take out 2 ml from each of the boiling tubes and carry out iodine test and Benedict’s test. 7. Record your observations in a table.
Note: Students need to rinse their mouth first before starting the experiment.
64
Chapter 3 : Nutrition
Thermometer Beaker P
Q
5 ml of starch suspension
Water bath at temperature 37°C 5 ml of starch suspension + 2 ml of saliva
Figure 3.15
Boiling tube P Q
Food test
Beginning of experiment
End of experiment
Iodine test Benedict's test Iodine test Benedict's test
Questions 1. Why does the temperature of the water bath need to be maintained at 37°C? 2. What happens to the starch in boiling tube Q at the end of the experiment? 3. What enzyme is found in our saliva?
Formative Practice
3.3
1. What is meant by digestion? 2. Complete the flow chart about the flow of food in the digestive tract.
3. Name three digestive enzymes and state their function. 4. A man with a tumour in his pancreas had a surgery to remove his pancreas. Explain the effect on the process of digestion.
65
3.4
Process of Absorption and Transportation of Digested Food and Defecation
O
bserve the surface of the bath towel in Photograph 3.11. What can you see? Observe the thread projections on the surface of the towel. Like the towel, the wall of our small intestine has millions of fine projections called villi. This increases the surface area for the process of absorption of digested food. Digested food which is made up of tiny molecules is easily absorbed into the blood circulatory system through the walls of the small intestine. These tiny molecules are then taken to every part of the body. Figure 3.16 shows the structure of a villus and the absorption of digested food in the small intestine.
Photograph 3.11 Thread projections on a towel
The surface of the small intestine has many folds to add to the surface area and increase the absorption rate of the products of digestion. The wall of the villus is very thin. It is one-cell thick to increase the rate of absorption. The function of the blood vessels in the small intestine is to transport nutrients to all parts of the body. (a) Villi on the walls of the small intestine Small sized nutrients that can go through the wall of the small intestine are transported by the blood to the cells. Blood capillaries
Undigested food that is larger cannot go through the small intestine wall Wall of the villus Lacteal
Science Villus - singular Villi - plural
Brain
Teaser
Why does our small intestine have more blood vessels than our stomach?
Science Lacteal absorbs digested fat in the villi of the small intestine. The lacteal transfers it into the lymphatic system and then to the blood circulatory system.
(b) Absorption and transportation of the products of digestion Figure 3.16 Structure of villus and absorption of digested food in the small intestine 66
Chapter 3 : Nutrition
Experiment 3.1 Aim: To study the absorption of glucose through a Visking tube. Problem statement: Can glucose diffuse through a Visking tube? Hypothesis: Glucose can diffuse through a Visking tube. Variables: (a) Constant variables: Type and size of Visking tube, temperature, time (b) Manipulated variable: Content in the Visking tube (c) Responding variable: Presence of glucose in the distilled water Materials: 1% starch suspension, glucose solution, Visking tube, iodine solution, Benedict's solution and distilled water Apparatus: Boiling tubes, beaker, test tubes, Bunsen burner, stopwatch, tripod stand, wire gauze and thread Procedure: 1. Soak two Visking tubes in water to soften them. 2. Tie up one end of both Visking tubes using thread. 3. Pour 10 ml of starch suspension into one Visking tube and 10 ml of glucose solution into the other Visking tube. 4. Tie up the other end of both Visking tubes using thread. 5. Rinse both Visking tubes using distilled water until clean. 6. Set up the apparatus as shown in Figure 3.17. 7. Carry out Benedict's test and iodine test on the distilled water in boiling tubes P and Q. 8. Record your observations in the following table. 9. Leave the apparatus for 30 minutes. Then, repeat step 7. 10. Record your observations in the following table.
Distilled water Starch solution Glucose solution Visking tube P
Figure 3.17
Q
Observation: Boiling tube P Q
Food test
Observation Beginning of experiment
End of experiment
Iodine test Benedict's test Iodine test Benedict's test
Questions 1. What is represented by the Visking tube and distilled water in the beaker? 2. State two precautionary steps that need to be taken when carrying out this experiment. 3. What inference can be made based on the observations of (a) boiling tube P? (b) boiling tube Q? 4. What conclusion can be made from this experiment?
3.4.1
67
Process of Transporting the Products of Digestion Food that is digested and absorbed into a villus needs to reach the cells of the body. The molecules that are absorbed into the villus will undergo assimilation. Assimilation is a process of distributing the end products of digestion for the use of the cells in our body. Our body uses the end products of digestion as follows: • Glucose is used to produce energy. • Amino acid is used to form component of cells. • Fatty acid and glycerol combine to form fat which is used as heat insulator and to protect internal organs. All these three systems below work together to ensure the digested food molecules reach the cells of the body. Digestive system
Breaks down large and complex particles of food into small and simple molecules so that they can be absorbed into the villi.
Blood circulatory system
Transports small and simple molecules to the cells of the body.
Assimilation
End products are distributed for: • formation of new cells • respiration • regulation of body temperature
Figure 3.18 Processes involved in the assimilation of digested food
A ctivity 3.8 Aim: To explain the process of transporting products of digestion by the blood to the cells of the body. Instruction 1. Work in groups. 2. Collect information from various sources on the process of transporting products of digestion by the blood to the cells of the body for assimilation. 3. Explain how the digestive system, blood circulatory system and respiratory system work together to fulfill the needs of our body. 4. Present the information obtained using a multimedia presentation. 68
3.4.2
Chapter 3 : Nutrition
Defecation What happens to the food that is not absorbed by the small intestine?
Undigested food and food that is not absorbed by the small intestine such as fibres, waste secretions of the digestive tract, dead cells and water will move into the large intestine. While moving through the large intestine, water and minerals are reabsorbed into the blood stream (Figure 3.19). This makes the unabsorbed and undigested food to become solid waste called faeces.
Blood vessel Large intestine
Rectum Anus
Figure 3.19
Faeces are stored temporarily in the rectum before being eliminated through the anus. The process of elimination of faeces from the body is called defecation.
A ctivity 3.9 Aim: To create a multimedia presentation about transportation and reabsorption of water by the large intestine and the process of defecation. Instruction 1. Get information from various sources on the: (a) importance of practising good eating habits to avoid constipation (b) implications to health if imbalanced diet is practised, especially with little or no fibres 2. Present the information using a multimedia presentation.
Formative Practice
3.4
1. The figure on the right shows the human large intestine. (a) Name X and state its function. (b) What is the movement that helps the movement of undigested food through the large intestine? (c) What is reabsorbed by the large intestine? 2. Kusairi does not like eating fruits and vegetables. What is the effect on his health?
3.4.3
X
69
70
Quiz
Water
Mineral
Fat measured by
Food pyramid
State of health
Climate
Type of work
Body size
Gender
Age
Balanced diet
Source
Mouth
food flow
Digestive system
Anus
Rectum
Large intestine
Small intestine
Duodenum
Stomach
Oesophagus
Importance of a balanced diet
Nutrition
Function
Calorific value of food
Carbohydrate
consists of
Food
Interactive Quiz 3
Fibre
Vitamin
Benedict's test
Alcoholemulsion test
Protein
Millon's test
Iodine test
food test
Summary
Glucose
1. Fatty acid 2. Glycerol
digested to become
Fat digested to become
Amino acid
digested to become
Carbohydrate Protein
Food digestion
Chapter 3 : Nutrition
SELF-REFLECTION After learning this chapter, you are able to: 3.1 Classes of Food Elaborate and communicate on classes of food. Test the presence of starch, glucose, protein and fat in food. 3.2 Importance of a Balanced Diet Elaborate and communicate on a balanced diet. Estimate calories of food intake in a meal and plan a balanced diet. Conduct a research and justify the importance of a balanced diet, exercise and a healthy lifestyle in order to maintain a healthy body. 3.3 Human Digestive System Elaborate and communicate on digestion. 3.4 Process of Absorption and Transportation of Digested Food and Defecation Conduct an experiment to explain the absorption of the end products of digestion. Relate the function of digestive system, blood circulatory system and respiratory system. Elaborate and communicate on defecation.
Summative
Practice
3
1. Figure 1 shows a food pyramid. Oil, fat, sugar
X
Figure 1
(a) Name three types of food in the space marked X. (b) State the functions of that food.
71
(c)
Amri is 15 years old and is obese. Amri has also been confirmed by the doctor as having diabetes. (i) Suggest practices that Amri needs to cultivate to control his health. (ii) Suggest a balanced breakfast menu that is suitable for Amri. (iii) In your opinion, what is the cause of his health problems? Justify your opinion.
2. Nicole lives in the Arctic which has a temperature as low as –40°C. (a) What class of food should Nicole consume continuously to adapt herself to the cold temperature?
P S
(b) Give reasons for your answer in 2 (a). 3. Figure 2 shows the human digestive system. (a) Identify parts P to W.
Q
T
(b) Name the part where (i) carbohydrate digestion begins (ii) protein digestion begins (iii) fat digestion begins 4. Amirah tested two types of food using iodine solution and Benedict's solution. Amirah’s observations are as follows.
U R
V W
Figure 2
• Rice – changes colour to dark blue with the iodine test, remains blue with the Benedict's test • Honey – remains brown with the iodine test, becomes a brick red precipitate with the Benedict's test (a) Explain how Amirah conducts the Benedict's test. (b) Create a table to show the results obtained by Amirah in both of the food tests. (c) What is the conclusion that can be made by Amirah? 5. Pui Yee conducted an experiment about the effect of heat on amylase. Amylase breaks down starch to maltose. • 2 ml of amylase solution is poured into two boiling tubes, A and B. • Only the solution in boiling tube A is heated. Then, the solution is left to cool down to room temperature. • 5 ml of starch suspension is added into boiling tubes A and B. • After 10 minutes, Pui Yee carries out tests for the presence of maltose. Pui Yee finds that maltose is present in boiling tube B only.
72
Chapter 3 : Nutrition
(a) What is the manipulated variable in this experiment? (b) State two constant variables in this experiment. (c) Pui Yee concludes that high temperature destroys amylase. Is her conclusion correct? Justify your answer.
HOTS
Mastery
3
6. Mr. Fuad and Mr. Razak live as neighbours in a village near the sea. Mr. Fuad is a fisherman while Mr. Razak teaches at a school in the village. Photograph 1 shows a set of breakfast for a healthy man.
Boiled egg
Sandwich
Tea
Watermelon
Photograph 1
(a) Study the set of food. State whether the set is more suitable for Mr. Fuad or Mr. Razak. Justify your answer. (b) Suggest a breakfast set that is suitable for the individual that you did not choose in 6(a). 7. Read the excerpt below and answer the questions that follow. A vegetarian does not eat meat, fish or chicken but only eats vegetables for personal reasons. Nevertheless, he can eat products that come from animals such as milk and cheese.
(a) In your opinion, is the vegetarian's diet healthy? Explain. (b) The vegetarian wants to make a burger. Plan a balanced burger menu for him. Explain.
73
Cha
er t p
4
Human Health
What are the differences between infectious and non-infectious diseases? How do infectious diseases spread? How are the microorganisms that enter the body killed?
Let’s understand: Infectious and non-infectious diseases Body defence
74
Bab Chapter 4 : Kesihatan 4 : HumanManusia Health
Science Blog
SCIENCE BLOG Zika Virus Have you heard about the Zika virus? This virus is transmitted by Aedes aegypti and Aedes albopictus mosquito. What are the symptoms experienced by people infected with Zika virus? This virus usually causes fever, rash, muscle pain, joint pain, headache and conjunctivitis. For infected pregnant women, the virus can cause serious birth defects in babies, where babies are born with underdeveloped heads and brain damage.
Keywords Infectious disease
Antibody
Non-infectious disease
Serum Active immunity
Pathogen
Passive immunity
Vector
Immunisation
Antigen
75
4.1
Infectious and Non-infectious Diseases
A
disease is an abnormal condition of body or mind that causes discomfort, difficulty to function or stress to an individual. Diseases can be classified into two, namely infectious diseases and non-infectious diseases. What are the differences between these two types of diseases?
Flu is an example of infectious disease.
Infectious disease • Caused by infection of pathogens directly through mediums and vectors. • Example: Tuberculosis, flu, ringworm, tinea, leptospirosis, dengue fever, malaria fever and Zika fever. • A disease that can be transmitted from one individual to another.
Asthma is a non-infectious disease.
Non-infectious disease • Caused by genetic factor or lifestyle. • Example: Cancer, hypertension, diabetes, asthma and cardiovascular diseases. • A disease that cannot be transmitted from one individual to another.
Figure 4.1 Differences between infectious and non-infectious diseases
How are Infectious Diseases Spread? Infectious diseases are spread by pathogens, the organisms that cause diseases. All virus, some bacteria, protozoa, fungi and worms are pathogens.
My
World How can we prevent infectious diseases like flu? I need to wear a face mask to cover my nose and mouth. If not, others can catch the flu.
76
4.1.1
Chapter 4 : Human Health
Science
Infectious diseases are spread by pathogens transmitted from an infected person (host) to another person through vectors and mediums such as water, air and contact. The host is a victim who is weak and easily infected. After getting infected, the host will show certain symptoms of the disease.
Not all microorganisms are pathogens that are harmful to health. There are some bacteria acting on food residue in the large intestine to produce vitamin K and vitamin B12 which are absorbed by the body.
Airborne diseases There are two ways airborne diseases are transmitted, through droplet transmission and dust transmission.
Figure 4.2 Ways of transmission of airborne diseases
Airborne diseases can be prevented by practising the following ways: cover the mouth and nose when sneezing, coughing or yawning do not spit everywhere avoid being in a crowded place ensure the living place gets enough light as ultraviolet rays can kill certain microorganisms in the air
Brain
Teaser
Why does influenza spread more rapidly during cold weather?
Example of diseases that can be spread through air are tuberculosis, flu, Severe Acute Respiratory Syndrome (SARS), Influenza A (H1N1) and chicken pox. H1N1 www.who.int
SARS http://www.infosihat.gov.my Info 4.1.2 4.1.3
Info 77
Waterborne diseases Infection through water usually happens in areas with inadequate water supply and poor sanitation. For instance, when someone uses a toilet built over a river, faecal pathogens enter the river and pollute the river. A person can be infected by pathogens when he drinks the contaminated water.
Other than inadequate water supply and poor sanitation, floods can also spread infectious diseases.
Photograph 4.1 Flood
Among the diseases that are transmitted through water include cholera, typhoid and amoebic dysentery. Infection of diseases through water can be prevented by the following ways:
Steps to Wash Hand Correctly http://www.infosihat.gov.my Info
add chlorine into swimming pools and water supply systems build toilets with good sanitation
boil drinking water properly
wash hands with soap after using the toilet Photograph 4.2 Steps to prevent waterborne diseases 78
Chapter 4 : Human Health
Infection of diseases through contact Two examples of diseases that can be transmitted through contact are ringworm and tinea. Both are caused by fungi. Accidentally touching the infected skin or wearing the clothes of an infected person will cause infections to occur.
Tinea
Diseases like syphilis and gonorrhoea can spread through sexual intercourse. Pathogens of these diseases are present in body fluids such as semen and vaginal fluid. The HIV virus that causes AIDS can also be transmitted through sexual intercourse, blood as well as exposure to syringesharing among patients and among drug addicts.
Ringworm Photograph 4.3 Diseases transmitted through contact
Infection of diseases through vectors Some pathogens are transmitted from one host to another new host through animals. Animals that transmit these pathogens are called vectors.
Brain
Teaser
Construct a bridge map for vectors and their pathogens.
Table 4.1Vector and pathogen Vector
Pathogen
1
Vector
Pathogen
Aedes mosquito
Zika virus
4
Cockroach
Salmonella typhi
2
5
Fly
Salmonella typhi
3
Aedes mosquito
Anopheles mosquito
Plasmodium malariae
Rat
Leptospira sp. bacteria
6
Dengue virus
79
Table 4.2 Several types of diseases, symptoms, pathogens, vectors and ways of infection Disease
Symptoms
Pathogen
Malaria
shivering, fever and sweating
Cholera
diarrhea and vomiting
Plasmodium malariae Vibrio cholerae bacteria
female Anopheles mosquito bite mosquito contaminated fly food and water
virus
Aedes mosquito
mosquito bite
virus
Aedes mosquito
mosquito bite
Salmonella typhi bacteria
cockroach, fly
contaminated food and water
rat
contaminated soil, food and water
Dengue Zika Typhoid Leptospirosis
joint pain, fever, headache and watery eyes fever, rashes, joint pain and conjunctivitis fever, intestinal bleeding and red rashes
fever, headache and muscle Leptospira sp. pain bacteria
Vectors
Way of infection
How Do Vectors Spread Diseases? Mosquitoes and flies are the two vectors that spread numerous infectious diseases. Let us see how these vectors spread diseases. Mosquito
Fly
1 A mosquito that already has pathogens
in its salivary glands sucks the blood of an uninfected person.
1
A fly that lands on dirt has pathogen on its legs and body.
1 2 Dirts
3
2
The mosquito secretes saliva when sucking the blood to prevent blood clotting. The infection spreads throughout the body of the person.
3
Another mosquito that bites the infected person transmits the disease to another victim.
2
The fly transmits the pathogens to the food.
Figure 4.3 Ways mosquitoes and flies spread diseases 80
3 The pathogens enter the body of the person who eats the contaminated food.
Chapter 4 : Human Health
The Mechanism to Prevent the Spread of Infectious Diseases How can infectious diseases be prevented from spreading? Prevention of infectious diseases involves three stages as shown in Table 4.3. Table 4.3 Three stages of prevention of infectious diseases Primary stage
Secondary stage
Tertiary stage
• Improving health ➟ Improving personal and family hygiene, cleanliness of living places and sanitation systems • Strengthening the body’s defence system ➟ Getting vaccines and immunisation for babies, children, pregnant women, food premises operators, hajj pilgrims and travellers. • Frequent health check-ups • Maintaining a healthy lifestyle ➟ Inhaling clean air ➟ Eating a balanced diet
• Determining transmission of infections through active and passive case detection ➟ Giving early treatment to patients ➟ Separating patients from others
• Controlling vector populations ➟ Destroying vector breeding and hiding places ➟ Fogging to kill vectors ➟ Enforcing laws by issuing compounds to owner of dirty food premises • Protecting hosts ➟ Using mosquito nets or mosquito coils ➟ Wearing thick clothes
Info
Prevent Dengue before Its too Late http://www.infosihat. gov.my/infosihat/media/ video/D/index.php
A ctivity 4.1 Aim: To carry out a case study on diseases in Malaysia.
Ministry of Health
Malaysia Instruction http://www.moh.gov.my 1. Work in groups. Info 2. Visit the website http://www.moh.gov.my. 3. Gather information on the statistics of infectious diseases from the website. 4. Discuss the following matters: (a) most common diseases in Malaysia (b) types of diseases transmitted, the causes and preventions (c) prediction of diseases progression based on the statistical graphs from Ministry of Health (d) suggestions to solve this problem 5. Present the outcomes using a multimedia presentation.
Formative Practice
4.1
1. What is meant by pathogen and vector? 2. Give one example of disease caused by (a) bacteria (b) virus (c) fungi 3. Give two examples of infectious diseases and two examples of non-infectious diseases. 4. State three ways infectious diseases are spread.
4.1.4
81
4.2
Body Defence
P
athogens enter the body through the respiratory system, digestive system, excretory system and skin. Pathogens need to be destroyed by the body. Do you know that our body has a strategy to defend itself against infections?
First line of defence
prevented
• Prevents pathogens from entering the body.
Skin
Pathogens that successfully get past the first line of defence enter the bloodstream and face the second line of defence.
Second line of defence
Non-specific body defence mechanism
Pathogen
• Fights pathogens through phagocytosis Pathogens that succeed in passing through the second line of defence will face the third line of defence.
Antibody
Third line of defence
Specific body defence mechanism
White blood cell
Antibody
Pathogen
• Fights pathogens by producing antibodies.
Pathogen Antibodies attach to pathogens (this prevents the pathogens from entering a host call)
Antibodies cause pathogens to clump together
Figure 4.4 Body defence mechanism 82
4.2.1 4.2.2
Chapter 4 : Human Health
Pathogens need to be destroyed!
First line of defence Skin • The human skin is made of a tough layer and is difficult to be penetrated by microorganisms. • Microorganisms can only get into the body if there is a wound or if the skin is injured. • Sweat and sebum secreted by the skin contain chemicals that can kill microorganisms. Mucous membrane • Mucous membrane is a membrane that lines the digestive tract and respiratory tract. • Microorganisms that enter the respiratory tract are filtered by nasal hairs and trapped by mucous lining the nasal cavity. • Earwax, tears and vaginal secretions also function as an antiseptic that kills microorganisms. Second line of defence Phagocytosis • White blood cells engulf and digest the pathogens using enzymes through phagocytosis.
White blood cell
Pathogen
Phagocytosis
Third line of defence Body immune system • Immunity is the ability of the body system to resist pathogens before it is infected. • It involves the production of antibodies when pathogens enter the body. • Antibody is a protein produced by white blood cells into the bloodstream in response to antigens. • An antigen is a foreign substance that comes from outside the body and induces the production of antibodies. Examples of antigens are pathogens, toxin molecules and blood cells from other blood groups.
83
A
ctivity
21
4.2
st
Century
Aim: To create a multimedia presentation on how the body defence system fights against infections and promotes healing. Instruction 1. Work in groups. 2. Gather information on: (a) body defence system fighting against infections (b) ways to promote healing from infections. 3. Present the outcomes using a multimedia presentation.
Importance of Immunisation Immunisation is an effort to stimulate the body defence against infections in babies, children and adults by injecting vaccines.
Is vaccination safe, especially for babies and children?
Yes, it’s safe! Vaccines used by the Ministry of Health Malaysia have been evaluated according to international standards.
A vaccine contains antigens obtained from a part or the whole structure of a weakened or dead virus or bacterium. Antigens stimulate the body's immune system, forming immunity against certain infections. Therefore, a baby needs to be injected with a few types of vaccines. Table 4.4 shows a vaccination schedule in Malaysia.
Vaccines http://www.infosihat.gov.my Info
84
4.2.3
Chapter 4 : Human Health Table 4.4 Vaccination schedule in Malaysia Age (Month)
(Year)
IMMUNISATION 0
2
3
5
DTaP
Dose 1
Dose 2
Dose 3
Booster
Hib
Dose 1
Dose 2
Dose 3
Booster
Polio (IPV)
Dose 1
Dose 2
Dose 3
BCG
Dose 1
Hepatitis B
Dose 1
Measles MMR
1
Dose 2
6
9
12
18
21
7
13
15
Dose 3
Booster Sabah only Dose 1
Dose 2
MR
Dose 2
DT
Booster Females only
HPV Tetanus JE (Sarawak)
Booster Dose 1
Dose 2
Source: Ministry of Health Malaysia
Notes: • • • • • • • •
Bacillus Calmette–Guérin (BCG) is a vaccine that gives protection against Tuberculosis. DTaP is the combination of Diphtheria, Tetanus and Pertussis. Hib is Haemophilus influenza type B. IPV is Inactivated Polio Vaccine that protects against Polio. MMR is the combination of Measles, Mumps and Rubella. MR is a booster dose to provide protection against Measles and Rubella. DT is a booster dose to protect against Diphtheria and Tetanus. HPV is Human Papillomavirus. This vaccine is given only for girls aged 13 years old. Dose 2 is given six months after dose 1. • JE is vaccine against Japanese Encephalitis. This vaccine is only given in Sarawak.
Passive Immunity and Active Immunity Immunity can be classified into two types, passive immunity and active immunity. Both immunities can be obtained naturally or artificially.
4.2.4
Science Antibiotics that we consume are excreted from our body and the dose will become less. Thus, antibiotics should be taken at the prescribed dose and time so that the antibiotics are always at the optimum level.
85
Natural
Passive immunity: The body gains antibody from external sources • Obtained when a baby receives antibody from breast milk or from the mother’s blood that flows across the placenta. • The immunity is temporary and short-lived, lasts for the first few months after the birth of the baby (Figure 4.5).
Concentration of antibody in the blood (%) Immunity level
Time (week)
Artificial
Figure 4.5 Graph of passive natural immunity • Obtained when an antiserum is injected into the patient’s body. • The antiserum fights against pathogens without interrupting the patient’s immune system. ■ Antiserum is a clear liquid in the blood that contains antibodies to prevent diseases. • The immunity is fast and temporary (Figure 4.6).
Concentration of antibody in the blood (%)
Immunity level
Time (week) First antiserum Second antiserum injection injection
Figure 4.6 Graph of passive artificial immunity Active immunity : The body produces its own antibodies when stimulated by antigens
• Occurs when a person recovers from an infection. • The immunity lasts long after the infection (Figure 4.7).
Concentration of antibody in the blood (%)
Natural
During the second time infection, the antibody produced exceeds the immunity level and immunity is achieved Immunity level During the first infection, the antibody produced is at a low level and does not achieve the immunity level Infection (week)
Figure 4.7 Graph of active natural immunity
Artificial
Concentration of antibody in the blood (%)
• Occurs when a vaccine that contains a dead or weakened pathogen is injected into the body, and the immune system responds by producing antibodies. • The immunity lasts long after the infection (Figure 4.8). First vaccine Second vaccine injection
Immunity level Time (week)
injection
Figure 4.8 Graph of active artificial immunity 86
Chapter 4 : Human Health
Strong Immune System The human body is made up of various systems including the immune system. When there is an imbalance in the body or too much toxins, the immune system becomes weak. Some of the causes that weaken the immune system and the practices that strengthen the immune system are shown in Photograph 4.4.
Causes that weaken the immune system
Exposure to polluted air
Exposure to pesticides
Stress
Excessive intake of sugar
Getting enough sleep and rest
Exercising and inhaling fresh air
Not smoking and no exposure to cigarette smoke
Doing periodic health examination
Science An allergy is the response of the body's immune system to allergen (cause of allergics) in the environment that is usually harmless for most people. Examples of allergens are mites, animal hair, dust, pollen, spores, food (seafood, milk and eggs), animal stings and some medicines.
Practices that strengthen the immune system
Photograph 4.4 Causes that weaken and practices that strengthen the immune system 4.2.5
87
21
A ctivity 4.3
st
Century
Aim: To gather information on the importance of immunisation and health level of individuals. Instruction 1. Work in groups. 2. Gather information on immunisation and the implications of the health level of individuals to the family, society, economy and nation. 3. Relate to the aspects of: (a) recurrence of controlled diseases such as leprosy, whooping cough and tuberculosis (b) increased costs of health care (c) affected quality of work (d) insurance coverage (e) quality of life (f) labour (migration) 4. Present the outcomes using a multimedia presentation.
Formative Practice
4.2
Immunity level
Infection time (week) Immunity P
Concentration of antibody in the blood (%)
Concentration of antibody in the blood (%)
1. Name two strategies of human body defence system. 2. What is meant by antigen, antibody and immunity? 3. The graphs below show two types of immunity, P and Q. 2nd infection
Immunity level 1st infection Infection time (week) Immunity Q
(a) Name immunity P and immunity Q. (b) Explain the similarities and differences between immunity P and immunity Q. (c) In your opinion, which immunity is better? Explain your answer. 4. Suggest two practices that weaken the immune system of a person. 5. Explain the reason why immunisation should be given to babies and children.
88
4.2.6
Chickenpox
H1N1
SARS
Flu
Typhoid fever
Amoebic dysentery
Tuberculosis
examples of diseases
examples of diseases
Cholera
Air
Water
Tinea
Ringworm
examples of diseases
Contact
ways of spreading
Infectious
Summary
Chikungunya
Zika fever
Malaria
Dengue fever
Leptospirosis
examples of diseases
Vector
Active
Natural
Immunity
Artificial
Passive
Natural
Diseases
Cardiovascular diseases
Quiz
Interactive Quiz 4
Importance
Artificial
Diabetes
Hypertension
Cancer
examples of diseases
Non-infectious
Chapter 4 : Human Health
89
SELF-REFLECTION After learning this chapter, you are able to: 4.1 Infectious and Non-infectious Diseases Differentiate and communicate infectious and non-infectious diseases. Explain how infectious diseases are spread. Separate the cause and spread of infectious diseases. Generate ideas on the mechanism to prevent the spread of infectious diseases. 4.2 Body Defence Elaborate and communicate the function of body defence system. Define antigens, antibodies and immunity. Justify the importance of immunisation. Differentiate passive immunity and active immunity. Justify good practices towards strong immune system. Justify and communicate the importance of immunisation and health level of individuals to the family, social, economy and nation.
Summative
Practice
4
1. The following are among the diseases recorded in Malaysia. Diabetes Leptospirosis
Flu Zika
Chickenpox Cholera
Hypertension Cancer
Heart attack Tinea
(a) Classify the diseases above into two groups based on their common characteristics. Disease
Group 1
90
Group 2
Chapter 4 : Human Health
(b) State the characteristic that you used to do the classification in 1(a). (c) Based on the list of diseases above, state a disease caused by each of the following factors. (i) Fungi (ii) Leptospira bacteria (iii) Influenza virus (iv) Unhealthy eating habits (d) Which disease is included in the immunisation programme for babies and children? 2. Dengue haemorrhagic fever is a fatal infectious disease. (a) Name the pathogen and vector for this disease. (b) Give one other example of disease spread through the same vector of dengue haemorrhagic fever. (c) Explain the way this disease is spread. 3. Photograph 1 shows a dustbin in a residential area. Predict the effects on the public if this situation prolongs. Give your reasons.
4. Figure 1 shows the graph of concentration of antibody in the blood (%) over a period of 40 days. Based on the graph, answer the following questions. (a) Explain the reaction of the body against the infection of virus A. (b) How long does it take for the body to build antibodies to reach the immunity level after an infection? (c) Give one reason why the antibody level drops after reaching the immunity level.
Concentration of antibody in blood (%)
Photograph 1
Immunity level
Exposed to virus A
0
Time 5 10 15 20 25 30 35 40 (day) Figure 1
91
5. Humans are lucky to have two types of body defence mechanisms, specific defence mechanism and non-specific defence mechanism. (a) Compare and contrast specific defence mechanism and non-specific defence mechanism. (b) Describe the strategy of (i) specific defence mechanism (ii) non-specific defence mechanism (c) Complete the table below by stating the type of immunity for each case. Case
Type of immunity
(i) Amin is not infected with chickenpox anymore as he had been infected with the disease when he was 7 years old. (ii) Kelvin is not infected with hepatitis B as he has obtained immunisation against the disease. (iii) A baby gets antibodies from breast milk. (iv) A patient with a hacking cough is injected with the antibody taken from an individual immune to the disease. 6. Assume you are a scientist. You are responsible to investigate a case of an infectious disease that has been spreading in a small town. The plague has caused three fatal cases and 10 more people have shown the symptoms of infection. (a) What are the precautionary steps that should be taken before you carry out the laboratory test to investigate the cause of the plague? (b) List down a few questions that you may ask the infected victims to help you in the investigation. (c) What are the steps that you can suggest to the residents of the town to protect those who are not infected yet? (d) The hospital has decided to impose quarantine on the infected people. Justify the hospital’s decision.
HOTS
Mastery
4
7. A farmer bought three hens and kept them in a chicken coop together with other 15 hens. After two days, the farmer found that the three new hens were infected with a disease. After few days, four more hens were infected with the disease. He called a veterinarian to help him. He told him about the three new hens and the change he made in the type of food for the hens a day before he found them sick. (a) Suggest two inferences on the infected hens. (b) If you were the veterinarian, how could you help the farmer to solve his problem? Explain the design of your test.
92
2
Exploration of Elements in Nature
urce of water?
What is the main so
rmed?
fo How is suspension
ption
for consum How is water safe produced? What is the use of daily life?
acids and alkalis in
93
Cha
er t p
5
Water and Solution
How is the water in an aquarium treated to make it safe for fish? Does a cooking oil bottle need to be shaken before use? What are the effects of water pollution on aquatic life? How are saturated solutions formed? Why is water known as a universal solvent?
Let’s understand: Physical characteristics of water Solution and rate of solubility Water purification and water supply
94
Chapter 5 : Water and Solution
Science Blog
SCIENCE BLOG Dead Sea The Dead Sea, located at the border of Jordan, is the saltiest sea in the world. Lying roughly 430.5 metres below sea level, it is the lowest point on Earth. The Dead Sea is completely surrounded by land. Thus, the water flowing from the Jordan River into the sea evaporates quickly, increasing its saltiness. Unusual high salt content causes the water in the Dead Sea to be so dense. This results in natural buoyancy, so, we can easily float in the Dead Sea.
Keywords Compound
Saturated solution
Capillary action
Universal solvent
Solubility
Oxidation
Suspension
Chlorination
Emulsion
Water sustainability
95
5.1
Physical Characteristics of Water
W
ater is a basic need of all life on Earth. No life would survive without water. More than 70% of the Earth’s surface is covered by water. Water has its own unique properties. Pure water is colourless, odourless and tasteless. It exists as liquid at room temperature. Figure 5.1 shows several physical characteristics of pure water. • • • •
Boiling point = 100°C Freezing point = 0°C Colourless Density = 1 g cm–3
Figure 5.1 Physical characteristics of pure water
Water has a high surface tension. Surface tension is a result of cohesive force between the molecules of water at the surface that allows insects like daddy longlegs to stay afloat on water (Photograph 5.1). Cohesive force between water molecules and adhesive force between water molecules and the cell walls of xylem allow water to be drawn up from the roots to the leaves of plants. This phenomenon is known as capillary action (Figure 5.2). Photograph 5.1 Daddy longlegs on the surface of water
Science Cell wall Adhesive force between water molecule and cell wall
Water molecule
Cohesive force between water molecules
• Attractive force between same molecules is cohesive force • Attractive force between different molecules is adhesive force
Figure 5.2 Capillary action in plant
Do you still remember the three states of water that you have learned in Form One? Absorption and release of heat to the surroundings result in the change of the state of water.
96
5.1.1
Chapter 5 : Water and Solution
Sublimation
Melting
Evaporation/ boiling
Freezing
Condensation LIQUID GAS
Sublimation
SOLID
Heat is absorbed Heat is released Figure 5.3 Effects of absorption and release of heat on the state of water
21
A ctivity 5.1
st
Century
Aim: To gather information and make a multimedia presentation on water. Instruction 1. Work in groups. 2. Gather the following information from various resources. (a) The importance of water for living things (b) Physical characteristics of water – Boiling point – Freezing point – Colour – Density – Surface tension – Capillary action – Effects of absorption and release of heat on water 3. Present your findings in the form of a multimedia presentation.
Composition of Water Teacher, is it true that water is a compound? How can we determine the composition of elements in a water molecule?
Yes, it is. Water is a compound which is made up of oxygen and hydrogen that combine chemically. We can determine the composition of elements in a water molecule through electrolysis.
97
A ctivity 5.2 Aim: To determine the composition of elements in a water molecule. Materials: Distilled water, dilute hydrochloric acid, wooden splinters and matches Apparatus: Electrolysis cell, switch, two measuring cylinders, dropper and crocodile clips
K
L Measuring cylinder
Carbon electrode
Distilled water + Dilute hydrochloric acid
Instruction 1. Label two measuring cylinders as K and L. 2. Set up the apparatus as shown in Figure 5.4 +– by adding a few drops of dilute hydrochloric acid to the distilled water. Switch Figure 5.4 3. Connect the switch for 10 minutes. 4. Observe the changes that occur at both measuring cylinders. 5. After 10 minutes, turn off the switch and record the volumes of gas in each measuring cylinder. 6. Test the gases collected using wooden splinters. (a) The gas in measuring cylinder K is tested with a glowing wooden splinter (b) The gas in measuring cylinder L is tested with a burning wooden splinter 7. Record all your observations in a table. Observation Measuring cylinder
Volume of gas (ml)
Effect on wooden splinter
K L Questions 1. Name the gases collected in measuring cylinders K and L. 2. (a) What is the ratio of the volume of gas in measuring cylinder K to L? (b) Give an inference for your answer in 2 (a). 3. Why is dilute hydrochloric acid added into the distilled water?
• During electrolysis, oxygen gas is produced at the anode while hydrogen gas is produced at the cathode. • A water molecule is made up of two hydrogen atoms and one oxygen atom. • The chemical symbol of water is H2O.
H O H
Science • Anode is the electrode that is connected to the positive terminal of a battery.
H
H O
O H
H
• Cathode is the electrode that is connected to the negative terminal of a battery.
Photograph 5.2 Composition of elements in water 98
Chapter 5 : Water and Solution
Effects of Impurities on the Melting Point and Boiling Point of Water Photograph 5.3 shows two pots containing water and chicken soup respectively. The pot containing water boils faster than the one containing chicken soup. Do you know the reason for this? Let us carry out Activity 5.3 to study the effects of impurities on the melting and boiling points of water.
(a) Water
(b) Chicken soup
Photograph 5.3 Effects of impurities on the boiling point of water
A ctivity 5.3 Aim: To observe the effects of impurities on the melting point and boiling point of water. Materials: Distilled water, ice cubes, two thick towels and table salt Apparatus: Beaker, conical flasks, thermometer, spatula, Bunsen burner, tripod stand, wire gauze, two-hole rubber stopper, glass tube and stopwatch A
The effect of table salt on the melting point of ice
Instruction 1. 2. 3. 4.
Wrap two similar-sized beakers in thick towels and label them as P and Q. Add the same number of ice cubes into both beakers. Add one spatula of salt into beaker P (Figure 5.5). Record the temperature of the ice in both beakers every 2 minutes until the temperature becomes constant.
Thermometer
Thermometer
P
Ice + table salt
Ice
Thick towel
Thick towel
Figure 5.5
Q
99
Observation Time (min) Temperature of ice in beaker (°C)
B
2
4
6
P Q
The effect of table salt on the boiling point of water
Instruction 1. Set up the apparatus as shown in Figure 5.6 and label the conical flasks as K and L. 2. Heat the distilled water in both conical flasks until they reach 80°C. 3. Start recording the temperature of the water in both conical flasks every 2 minutes until the temperature becomes constant. Thermometer Glass tube Conical flask
K
L
Distilled water Distilled water+ table salt
Wire gauze
Bunsen burner
Wire gauze
Bunsen burner
Tripod stand Figure 5.6
Observation Time (min) Temperature of water in conical flask (°C)
2
4
6
K L
Questions 1. Using the Kinetic Theory of Matter, explain the change in the state of ice in Activity A. 2. Give an inference for the boiling point of distilled water and the boiling point of distilled water mixed with salt. 3. What can be concluded about impurities from Activity A and B?
After completing Activity 5.3, you will find that salt lowers the melting point of ice and increases the boiling point of water. Other physical characteristics of water such as taste, smell and colour can also change in the presence of impurities. For example, seawater tastes salty because it contains dissolved salt. 100
Chapter 5 : Water and Solution
Evaporation of Water Evaporation of water is the process that happens at the surface of water that changes water to water vapour. This process occurs at any temperature. The changes in the water molecules that undergo evaporation can be seen in Figure 5.7. Water vapour The molecules of water at the surface have higher kinetic energy, thus they can move faster and escape into the air.
Photograph 5.4 Evaporation of water occurs when wet clothes dry
Figure 5.7 The process of water evaporation
Let us carry out Experiment 5.1 to know the factors affecting the rate of evaporation of water.
Experiment 5.1 Aim: To study the factors affecting the rate of evaporation of water. A
Humidity
Problem statement: Does humidity affect the rate of evaporation of water? Hypothesis: The higher the humidity, the lower the rate of evaporation of water. Variables: (a) Constant variables: Surrounding temperature, volume of water, movement of air and exposed surface area of water (b) Manipulated variable: Humidity (c) Responding variable: Rate of evaporation of water Materials: Anhydrous cobalt chloride papers, water, thread and anhydrous calcium chloride Apparatus: Bell jar and beaker Procedure: 1. 2. 3. 4.
5.1.2
Dip two anhydrous cobalt chloride papers into water until completely wet. Set up the apparatus as shown in Figure 5.8. Observe the cobalt chloride papers. Record your observations in a table.
101
Thread Wet cobalt chloride paper
Bell jar
Anhydrous calcium chloride
Beaker
Water R
B
Wet cobalt chloride paper
Figure 5.8
S
Science
Surrounding temperature
Problem statement: Does surrounding temperature affect the rate of evaporation of water? Hypothesis: The higher the temperature of surrounding, the higher the rate of evaporation of water Variables: (a) Constant variables: Humidity, volume of air, movement of air, exposed surface area of water (b) Manipulated variable: Surrounding temperature (c) Responding variable: Rate of evaporation of water
Cobalt chloride paper is made of cobalt chloride powder, a substance that is very sensitive to water. The paper is blue when dry and turns pink when wet.
Materials: Anhydrous cobalt chloride papers and water Apparatus: Filament lamp and white tile Procedure: 1. Label two anhydrous cobalt chloride papers as J and K. 2. Dip both papers, J and K in water until completely wet. 3. Place papers J and K on a table as shown in Figure 5.9. 4. Observe the cobalt chloride papers. 5. Record your observations in a table.
Wet cobalt chloride papers
Filament lamp White tile J
K Figure 5.9
102
Chapter 5 : Water and Solution
C
Exposed surface area of water
Problem statement: Does exposed surface area of water affect the rate of evaporation of water? Hypothesis: The larger the exposed surface area of water, the higher the rate of water evaporation. Variables: (a) Constant variables: Humidity, volume of air, movement of air and surrounding temperature (b) Manipulated variable: Exposed surface area of water (c) Responding variable: Rate of evaporation of water Materials: Filter papers, water and thread Apparatus: Retort stand with clamp Procedure: 1. Prepare three filter papers, P, Q and R. 2. Dip all the three filter papers in water. 3. Fold filter paper Q into two and filter paper R into four. 4. Hang all the three filter papers on different retort stands (Figure 5.10).
Retort stand with clamp
Thread Filter paper P
Retort stand with clamp
Thread Filter paper Q
Thread
Retort stand with clamp
Filter paper R
Figure 5.10
5. Record the time taken for the filter papers to dry in a table. D
Movement of air
Problem statement: Does movement of air affect the rate of evaporation of water? Hypothesis: The faster the movement of air, the higher the rate of evaporation of water. Variables: (a) Constant variables: Humidity, volume of water, exposed surface area of water and surrounding temperature (b) Manipulated variable: Movement of air (c) Responding variable: Rate of evaporation of water Materials: Anhydrous cobalt chloride papers, cellophane tape and water Apparatus: Microscope slides, fan and dropper
Anhydrous cobalt chloride paper
Cellophane Microscope Cellophane tape tape slide M
N Figure 5.11
Procedure: 1. Stick two anhydrous cobalt chloride papers on microscope slides using cellophane tape and label them as M and N (Figure 5.11). 2. Add a few drops of water on each cobalt chloride paper. 3. Place slide M under a moving fan and slide N away from the fan. 4. Record your observations after 15 minutes in a table. 103
Conclusion: Is the hypothesis for each experiment accepted? Give your reasons. Questions 1. State the functions of water and anhydrous calcium chloride in Experiment A. 2. What is the use of the filament lamp in Experiment B? 3. How does surface area affect the rate of evaporation of water? 4. Why is a fan used in Experiment D?
There are four factors affecting the rate of evaporation of water, humidity, surrounding temperature, exposed surface area of water and movement of air.
Brain
Why do we feel cold when we sweat?
temperature
Humidity
g Surroundin
Dry air contains less water vapour. So, dry air can hold more water molecules that escape from the surface of water. Thus, the rate of evaporation of water increases.
When the surrounding temperature increases, the water molecules at the surface gain more energy, move faster and escape into the air easily. Thus, the rate of evaporation of water increases.
ea of water Exposed surface ar Exposed surface area of water that is larger allows more water molecules to escape, thus increasing the rate of evaporation of water.
f air Movement o Movement of air sweeps away water vapour in the air. High speed of wind causes the air at the surface of water to dry and increases the rate of evaporation of water.
Figure 5.12 Factors affecting the rate of evaporation of water
104
Teaser
Chapter 5 : Water and Solution
Applications of Evaporation of Water in Daily Life
Clothes hung on clothes lines have large exposed surface areas. So, the clothes will dry faster.
Sea salt is obtained from the evaporation of seawater.
Seafood that is dried can be kept longer as microorganisms cannot survive without water.
Hair dryer that blows hot air increases the temperature, thus increasing evaporation of water.
Photograph 5.5 Applications of evaporation of water in daily life
21
A ctivity 5.4
st
Century
Aim: To create a multimedia presentation on evaporation of water. Instruction 1. Work in groups. 2. Gather information on: (a) the relationship between evaporation process and daily life activities (b) the ways to reduce water loss through evaporation process in agriculture (c) cooling through evaporation process in refrigerators 3. Use various resources such as Internet and library to gather information for 2 (a), (b) and (c). 4. Present the outcomes.
Formative Practice
5.1
1. Ikram needs pure water to prepare a solution. His friend gave him a bottle of water. Suggest a way that he can use to determine whether the water is pure or not. 2. Explain the difference between the movement of water molecules at room temperature and at 0°C. 3. Explain one importance of evaporation of water to the human body.
105
5.2
Solution and Rate of Solubility
Sugar (solute)
Solute, Solvent and Solution
H
ave you ever wondered what happens to the sugar that is added to water? Solute is a substance that can dissolve in a liquid, whereas solvent is a liquid that dissolves a substance. Thus, sugar is a solute and water is a solvent. Solution is the mixture formed when a solute dissolves in a solvent. Thus, the sugar water formed is a solution (Photograph 5.6).
Water (solvent)
Sugar water (solution)
Photograph 5.6 Formation of solution
Dilute Solution, Concentrated Solution and Saturated Solution
The amount of solute in a solution affects the concentration of the solution. The solutions formed can be classified as dilute solution, concentrated solution and saturated solution. These solutions can be prepared in the laboratory by carrying out Activity 5.5.
A ctivity 5.5 Aim: To prepare dilute solution, concentrated solution and saturated solution. Materials: Distilled water and copper(II) sulphate crystal Apparatus: Beaker, measuring cylinder, glass rod and spatula Instruction 1. Fill three beakers labelled as P, Q and R with 50 ml of distilled water (Figure 5.13). 2. Add two spatulas of copper(II) sulphate crystals into beaker P and stir until all the copper(II) sulphate crystals dissolve. 3. Add four spatulas of copper(II) sulphate crystals into beaker Q and stir until all the copper(II) sulphate crystals dissolve. 4. Add four spatulas of copper(II) sulphate crystals into beaker R and stir until all the copper(II) sulphate crystals dissolve. Add more copper(II) sulphate crystals little by little until excess copper(II) sulphate crystals deposit at the bottom of the beaker. 5. Observe all the three beakers and record your observations.
50 ml of distilled water
P
Q
R
Figure 5.13
Observation Beaker
Quantity of copper(II) sulphate crystals
Colour of solution
P Q R
106
5.2.1
Chapter 5 : Water and Solution
Questions 1. Identify the types of solutions formed in beakers P, Q and R. 2. Name the solute, solvent and solution used in this activity. 3. Why does a precipitate form in beaker R?
The three types of solutions formed in Activity 5.5 are uniform mixtures even though the saturated solution forms a precipitate. Table 5.1 shows the comparison between these three types of solutions. Table 5.1 Comparison between different types of solutions Dilute solution
Concentrated solution
• Less amount of solute in the solvent • Can dissolve more solute
• More amount of solute in the solvent • Can dissolve less solute
Saturated solution • Excess amount of solute in the solvent • Cannot dissolve any more solute and form precipitate
Solution and Suspension When two substances are mixed to form a mixture, a solution or a suspension is formed. What is the difference between a solution and a suspension? Solution is a clear mixture formed when a solute dissolves in a solvent, whereas suspension is a cloudy mixture formed from undissolved solute particles in a solvent. Figure 5.14 shows river water that contains a non-uniform mixture of water and sand.
Brain Suspension Mixture of water and small sand particles
Teaser
What is the type of solution found in the Dead Sea?
Undissolved sand particles
Figure 5.14 River water is an example of suspension 107
Let us carry out Activity 5.6 to distinguish between a solution and a suspension.
A ctivity 5.6 Aim: To distinguish between a solution and a suspension. Materials: Copper(II) sulphate crystal, water, filter paper and chalk powder Apparatus: Beaker, spatula, conical flask, filter funnel, measuring cylinder, glass rod, torchlight and white screen Instruction 1. Measure and pour 100 ml of water into a beaker and add one spatula of copper(II) sulphate crystals. 2. Stir the mixture until even and observe the appearance of the mixture formed. 3. Use a torchlight to direct a beam of light towards the beaker and observe whether the light can pass through the mixture as shown in Figure 5.15(a). 4. Let the mixture stand for 10 minutes and filter its content as shown in Figure 5.15(b). 5. Observe if there is any residue left on the filter paper. 6. Repeat steps 1 to 5 by replacing copper(II) sulphate crystals with chalk powder and record your observations. Mixture
Mixture White screen
Torchlight
Filter paper
Residue
Beaker
(a)
Glass rod Filter funnel
Filtrate Figure 5.15
Conical flask
(b)
Questions 1. What is the appearance of the mixture of water and chalk powder? 2. How can the solute in the mixtures be related to the ability of light to pass through them? 3. Give your inference for the filtration test done on both mixtures.
A solution is formed when a solute is dispersed throughout a solvent. Thus, a solution has a uniform colour and appearance. World My Although the mixture of water and copper(II) sulphate crystals A medicine in the form of forms a coloured solution, the uniform colour of the mixture makes suspension must be shaken the solution appear transparent. The tiny size of the solute particles before using to ensure allows light to pass through a solution. This is also the reason why the active substances in there is no residue left when a solution is filtered. it are equally dispersed throughout the liquid. A suspension appears cloudy as the solute particles do not dissolve in the solvent, such as chalk powder that is insoluble in water. The size of the particles in a suspension is large enough to prevent light from passing through the suspension. Suspensions will settle if left undisturbed and leave residue when filtered. 108
Chapter 5 : Water and Solution
Solubility You have already learned the definition of a solution. Now, what does solubility mean? Solubility of a solute is the maximum amount of the solute that can dissolve in 100 ml of solvent at a specific temperature.
Rate of Solubility The rate of solubility of a substance is affected by several factors. Carry out Experiment 5.2 to determine these factors.
Experiment 5.2 Aim: To study the factors affecting the rate of solubility. A
Temperature of solvent
Problem statement: Does the temperature of solvent affect the rate of solubility? Hypothesis: The higher the temperature of solvent, the higher the rate of solubility. Variables: (a) Constant variables: Volume of solvent, rate of stirring and size of solute (b) Manipulated variable: Temperature of solvent (c) Responding variable: Rate of solubility Materials: Distilled water and table salt Apparatus: Measuring cylinder, beaker, glass rod, thermometer, tripod stand, wire gauze, Bunsen burner and spatula Procedure: 1. Pour 100 ml of distilled water into beakers labelled K and L. 2. Heat beaker L until 50°C, then add table salt into beakers K and L. 3. Stir the mixtures in beakers K and L at the same rate until the salt dissolves completely (Figure 5.16). 4. Observe and determine the beaker in which the salt dissolves faster. 5. Record your observation. Glass rod Thermometer Beaker L Table salt
Glass rod Beaker K Table salt
100 ml of distilled water
100 ml distilled water Bunsen burner
Figure 5.16
Conclusion: Is the hypothesis accepted? Give your reason.
5.2.2
109
B
Rate of stirring
Problem statement: Does the rate of stirring affect the rate of solubility? Hypothesis: The higher the rate of stirring, the higher the rate of solubility. Variables: (a) Constant variables: Volume of solvent, temperature of solvent and size of solute (b) Manipulated variable: Rate of stirring (c) Responding variable: Rate of solubility Materials: Distilled water and table salt Apparatus: Beaker, glass rod, measuring cylinder and spatula Procedure: 1. Set up the apparatus as shown in Figure 5.17. 2. Stir the mixture in beaker K slowly and the mixture in beaker L fast. 3. Determine in which beaker the salt dissolves faster. 4. Record your observation.
Stirred slowly
100 ml distilled water
Beaker K
Beaker L
2 g table salt
Conclusion: Is the hypothesis accepted? Give your reason. C
Stirred fast Glass rod
Figure 5.17
Size of solute
Problem statement: Does the size of solute affect the rate of solubility? Hypothesis: The smaller the size of solute, the higher the rate of solubility. Variables (a) Constant variables: Volume of solvent, temperature of solvent and rate of stirring (b) Manipulated variable: Size of solute (c) Responding variable: Rate of solubility Materials: Distilled water, fine sugar and sugar cubes Apparatus: Beaker, measuring cylinder, glass rod and spatula Procedure: 1. Set up the apparatus as shown in Figure 5.18. 2. Stir the mixtures in beakers K and L at a same rate. 3. Determine in which beaker the sugar dissolves faster. 4. Record your observation.
Glass rod Beaker K
Conclusion: Is the hypothesis accepted? Give your reason.
110
1 g of fine sugar
Beaker L
100 ml distilled water 1 g of sugar cube
Figure 5.18
Chapter 5 : Water and Solution
Summary: Factor
Rate of solubility
Temperature Rate of stirring Size of solute
We use the knowledge of solubility in our everyday life without even realising it. For example, to make a cup of coffee quickly, we use hot water, fine sugar and instant coffee powder. Then, the mixture is stirred fast. All these actions increase the rate of solubility. Fine sugar dissolves faster compared to sugar cubes.
Sugar dissolves faster in hot coffee when stirred.
High temperature and rate of stirring of solvent cause the particles to move rapidly. This causes the particles of solvent and solute to fill up the spaces between them faster.
The smaller the size of solute, the bigger the total surface area that is exposed to the solvent particles. This allows the solute to dissolve faster in the solvent.
Photograph 5.7 Factors affecting the rate of solubility
Colloid A colloid is a mixture of two or more solutes dispersed evenly in a solvent. However, colloids neither form a clear mixture nor precipitate. Thus, colloids are intermediate between a solution and a suspension (Figure 5.19).
Solution
Colloid
Suspension
Figure 5.19 5.2.3
111
Foam – shaving cream
Emulsion – milk, mayonnaise Photograph 5.8 Examples of colloids in everyday life
Water as a Universal Solvent Water is known as a universal solvent due to its ability to dissolve almost all substances, solids, liquids or gases. Water is used as a solvent in domestic use and also as a raw material in the manufacturing industry, agriculture and medicine.
Fertilisers dissolve in water and are absorbed by the roots of plants.
Soft drinks are produced using water as a solvent.
Water dissolves detergents used in cleaning process.
Photograph 5.9 Uses of water as a universal solvent
Organic Solvents Organic solvents which are carbon-based can be used to dissolve solutes that are insoluble in water. Organic solvents Alcohol
Kerosene
Acetone
Turpentine
Ether
Perfume
Lamp oil
Nail varnish
Paint remover
Oil extractor
Lacquer
Paint thinner
Antiseptic
Figure 5.20 Examples of organic solvents in everyday life
The characteristic of organic solvents which is volatile enables these solvents to be used widely in manufacturing aerosol substances such as spray paint, perfumes and pesticides. Organic solvents must be handled carefully as there are certain organic solvents which can be harmful to health.
112
5.2.4 5.2.5
Chapter 5 : Water and Solution
Formative Practice 1. 2. 3. 4.
5.2
Explain with examples the meaning of solute, solvent and solution. Explain one difference between solution and suspension. Name the substances at home that can remove rust, blood stains and ink stains. Why is hot water suitable for making coffee?
5.3
Water Purif ication and Water Supply
Water Purification Method
W
ater is one of the most valuable natural resources on Earth. Water covers two-thirds of the Earth’s surface, however most of the water cannot be used directly as it contains impurities, microorganisms and dissolved substances. Thus, water needs to be purified and treated in order to be safe for human consumption. Water purification can remove odour, taste, colour, microorganisms and dissolved substances so that the water can be used for various purposes. Let us carry out Activity 5.7 to study the water purification method.
A ctivity 5.7 Aim: To study various water purification methods. Materials: Pond water, chlorine water, sterile nutrient agar, filter paper and cellophane tape Apparatus: Beaker, glass rod, filter funnel, measuring cylinder, Bunsen burner, wire gauze, Petri dish, distillation flask, Liebig condenser, retort stand with clamp, thermometer and one-hole rubber stopper Instruction 1. 2. 3. 4.
Set up the apparatus as shown in Figure 5.21(a) and collect the filtrate. Set up the apparatus as shown in Figure 5.21(b) and collect the distillate. Prepare five Petri dishes containing nutrient agar and label them as A, B, C, D and E. Add the following substances into the Petri dishes. Petri dish A is added with five drops of pond water Petri dish B is added with five drops of filtrate of pond water Petri dish C is added with five drops of distillate of pond water Petri dish D is added with five drops of boiled pond water Petri dish E is added with five drops of pond water mixed with chlorine water 5. Close all the Petri dishes and seal them with cellophane tape. 6. Keep all the Petri dishes in a dark place for four days. 7. After four days, observe and record the growth of microorganisms on the nutrient agar.
5.3.1
113
Thermometer
Glass rod
Water out
Beaker Pond water
Filter paper
Liebig condenser
Filter funnel Measuring cylinder
Filtrate
Figure 5.21(a)
Pond water
Distillation flask Water in Bunsen burner
Distillate
Figure 5.21(b)
Observation Petri dish
Observation
A B C D E Questions 1. Which method produces pure water? 2. What is the function of chlorine in Petri dish E? 3. Give an inference for your observation on the nutrient agar in Petri dishes B and C.
You have studied water purification methods from Activity 5.7. Overall, water purification methods include boiling, chlorination, filtration and distillation (Figure 5.22).
Boiling To kill microorganisms
Chlorination To kill microorganisms
Water purification methods
Figure 5.22 Water purification methods 114
Filtration To separate suspended particles from liquid
Distillation To separate suspended particles, dissolved substances and kill microorganisms
Chapter 5 : Water and Solution
Solving the Problems of Water Supply Some countries with limited water sources use alternative ways to get water supply to meet their nations’ water needs.
Info
NEWater https://www.pub. gov.sg/watersupply/ fournationaltaps/newater
Singapore has limited water supply. The country uses modern technologies to recycle sewage into drinking water and for industrial uses. This project is known as NEWater.
STEM
A ctivity 5.8
Aim: To gather information on the initiatives taken by countries with water shortage to get water supply. Instruction 1. Work in groups. 2. Gather information on how the countries with water shortage find alternatives for water supply. The alternative methods include: (a) recycle of water (b) fog harvesting (c) water purification from seawater (reverse osmosis) 3. Present the outcomes using a multimedia presentation.
STEM A water treatment engineer designs a system that can treat wastewater into clean water which is safe for human use.
Water Supply System We use water every day for bathing, drinking, washing the dishes as well as many other things. Have you ever wondered where the tap water comes from? Water collected from sources such as rivers and rain is conveyed to water treatment plants prior to its distribution to consumers. Bacteria, algae and minerals are some of the substances removed during the water purification process (Figure 5.23 and Figure 5.24). Teacher, why is water purification necessary?
Water purification is essential to remove odour, colour, taste, microorganisms and harmful chemicals so it is safe for consumption.
5.3.2
115
Oxidation Water reservoir
Filtration
Pump station
Slaked lime Alum (Calcium hydroxide)
Sedimentation
Coagulation
Filtration
Fluoride compound Chlorine
Chlorination and fluoridation
To homes
Clean water tank
Storage tank
Figure 5.23 The water supply system 116
Pump
Chapter 5 : Water and Solution
Process
Function
Filtration
Removes large suspended particles such as tree branches and leaves
Oxidation
Increases oxygen content in the water to get rid of unpleasant smell and taste
Coagulation
• Alum is added so that mud particles stick together and sink to the bottom of the tank • Slaked lime (calcium hydroxide) is added to reduce the acidity of water
Sedimentation
Suspended particles deposit at the bottom of the tank
Filtration
Removes remaining suspended particles through sand filters
Chlorination and fluoridation
• Chlorine is added to kill microorganisms in water • Sodium fluoride is added to prevent tooth decay
Figure 5.24 Water purification process
A ctivity 5.9
STEM
21
st
Century
Aim: To gather information on the stages of the water supply system. Instruction 1. Work in groups. 2. Build a model of water supply system using scrap materials to show the following stages: (a) filtration (d) sedimentation (b) oxidation (e) filtration (c) coagulation (f ) chlorination and fluoridation 3. Gather information about each stage. 4. Explain the model built and present the outcomes.
5.3.3
117
Water Sustainability Rivers are the main water source in Malaysia. Unfortunately, water pollution makes the water unsuitable for consumption and also results in negative impacts on the environment (Photograph 5.10). Development projects, industrial and agricultural activities are among the main sources of water pollution. Figure 5.25 shows the main water pollutants and ways to overcome water pollution. Photograph 5.10 Water pollution Water pollutants
Ways to overcome water pollution
Domestic waste • Upgrade sewerage systems nationwide • Educate people on how to manage rubbish correctly • Improve sanitation facilities in rural areas
Industrial waste
Chemicals in agriculture
• Enforce laws to ensure industrial waste is treated before being discharged into the river. Examples of laws on water pollution: • Environmental Quality (Scheduled Wastes) Regulations 2005 • Environmental Quality (Industrial Effluent) Regulations 2009 • Environmental Quality (Sewage) Regulations 2009
• Educate farmers to use biodegradable fertilisers and pesticides.
Oil spillage • Surround and contain oil spilled at sea using National Oil Spill Contingency Plan Revised Year 1999/2000. • Improve air surveillance with the cooperation of Air Police Unit. Figure 5.25 Water pollutants and the ways to overcome water pollution 118
5.3.4
Chapter 5 : Water and Solution
A ctivity 5.10 Aim: To discuss water sustainability. Instruction 1. Work in groups. 2. Gather information on one of the topics below: (a) the importance of realising safe water content for consumption (b) effects of water pollution on living things and environment based on real cases such as mercury poisoning in Minamata Bay, Japan (c) river pollution and river cleaning methods (d) the role of individuals in ensuring water sustainability 3. Share the outcomes.
STEM
A ctivity 5.11
21
st
Century
Aim: To carry out water audit activity. Instruction 1. Work in groups. 2. Based on the water bills of the past few months, calculate the average water consumed at home or school. 3. Identify the acts of wasting water and record them. 4. Discuss and suggest water conservation steps. 5. Think of an innovative method to conserve water and increase efficiency of water usage. 6. Write a report.
Formative Practice 1. 2. 3. 4.
5.3
Name three impurities found in natural water resources. State water purification methods that can remove impurities in water. What are the major water pollution problems in coastal areas and in the sea? Determine whether the following statements are True or False. Write your answers in the space provided. Statement
True / False
(a) River water and sewage are natural water resources. (b) Alum and slaked lime are added in the coagulation tank. (c) Chlorination can remove impurities in the water. 5. Explain three ways to control water pollution.
119
120
Quiz
2 hydrogen atoms
Interactive Quiz 5
Surface tension
Density
Colour
Freezing point
Boiling point
Physical characteristics of water
Summary
Chlorination
Boiling
Distillation
Filtration
Saturated solution
Water purification system
Water supply system
Solute
Organic
Ways to overcome
Water pollutants
Sources of pollution
Water sustainability
Size of solute
Rate of stirring
Temperature of solvent
Water (universal solvent)
Solvent
Concentrated solution
factors affecting the rate of solubility
Solution
Water purification and supply
Movement of air
Exposed surface area of water
Surrounding temperature
Humidity
factors affecting
Evaporation of water
Water and solution
Water purification method
1 oxygen atom
composition
Water
types
Dilute solution
Chapter 5 : Water and Solution
SELF-REFLECTION After learning this chapter, you are able to: 5.1 Physical Characteristics of Water Elaborate and communicate about water. Carry out experiments and communicate about the water evaporation process in daily life. 5.2 Solution and Rate of Solubility Explain with examples the meaning of solution and solubility. Carry out experiment to determine the factors affecting the rate of solubility. Explain with examples the meaning of colloids in daily life. Elaborate and communicate the uses of water as a universal solvent in daily life and manufacturing industry. Demonstrate examples of organic solvents and their uses in daily life. 5.3 Water Purification and Water Supply Demonstrate the water purification method. Solve problems in getting water supply for daily life usage. Build a model and communicate about water supply system. Justify water sustainability as a key to healthy living.
Summative
Practice
5
1. Johan started attending swimming lessons . On the first day, he suffered from pain on his body as he had used a wrong technique to jump into the water (Photograph 1). Explain the reason for Johan’s injury. (Relate to water surface tension). 2. Aliya carried out an investigation to study the type of solution formed when a solute is dissolved in a solvent. She found that three spatulas of salt produced a saturated solution when dissolved in 50 ml of water.
Photograph 1
(a) Draw the particles of the salt water produced when: (i) one spatula of salt is added into 50 ml of water (ii) five spatulas of salt are added into 50 ml of water (b) Does heating the water increase the rate of solubility? Give your explanation.
121
3. Figure 1 shows the water evaporation process. Water molecule escapes
Water surface Water
Water molecule
Figure 1
(a) Explain the process above using the Kinetic Theory of Matter. (b) State four factors that affect the water evaporation process. Explain two of them. (c) Which of the following shows the composition of elements in water? Tick (3) the correct answer. (i)
(ii)
(iii)
(iv)
4. Match the following substances to the correct type of compound. (a) Salad sauce (b) Apple juice (c) Blood (d) Carbon dioxide in water (e) Mixture of water and chalk (f ) Milk (g) Vinegar 5. Suggest an organic solvent that can be used to remove chlorophyll stain.
122
Colloid Suspension Solution
Chapter 5 : Water and Solution
6. K, L, M and N are the stages involved in the water purification system. K : Coagulation L : Chlorination
M : Sedimentation N : Filtration
(a) Arrange K, L, M and N in a correct sequence. (b) Name two chemicals used to treat water in water treatment plants. State the functions of both substances. (c) How is the process in stage K done? (d) Predict what will happen if the mixture is stirred in stage N. 7. Vicki carried out an activity to study several water purification methods. She used cloudy river water as her study sample. Sample A : Filtered Sample B : Boiled Sample C : Distilled Sample D : Added chlorine (a) Which sample would become clear? (b) Which sample would still contain suspended particles? (c) Which sample would turn to pure water? (d) In which sample would microorganisms be removed?
HOTS 8.
Mastery
5
Water pollution is one of the major problems faced by our country. Based on the situation above, prepare a poster on water pollution and its effects on humans.
9.
You are required to distinguish between two unknown substances blindfolded. You were told that the two substances are a mixture. What are the questions you would ask to identify the types of mixture?
123
Cha
er t p
6
Acid and Alkali
Why do certain fruits taste sour? What is the pH of pure water? Is a bee sting acidic?
Let’s understand: Properties of acid and alkali Neutralisation
124
Chapter 6 : Acid and Alkali
Science Blog
SCIENCE BLOG The pH of Human Skin The human skin acts as a natural barrier to fight infection by pathogens. The skin pH level plays an important role in fighting these infections. Our skin has a thin protective layer known as acid mantle. This layer which is made of a combination of an oily substance (sebum) and sweat makes the skin acidic and protects the skin from the external environment.
Keywords Corrosiveness
Universal indicator
Blue litmus paper and red litmus paper
pH scale
pH value
Titration
Phenolphthalein
Neutralisation
125
6.1
Properties of Acids and Alkalis
T
ry to recall the knowledge of acids and alkalis that you have learned in primary school. Acids and alkalis can be found in various substances used in our daily lives. What are the acidic and alkaline substances that you know? Table 6.1 Examples of acids and alkalis Acid
Alkali
Hydrochloric acid
Sodium hydroxide solution
Vinegar
Soap water
Photograph 6.1 Orange juice is an acidic substance What is the origin of the word ‘acid’?
The word ‘acid’ comes from the Latin word, acidus which means sour, whereas the word ‘alkali’ comes from the Arabic word, alqali which means ashes of plants.
Let us carry out Activity 6.1 to study the properties of acids and alkalis.
A ctivity 6.1 Aim: To study the properties of acids and alkalis. Materials: Dilute hydrochloric acid, concentrated hydrochloric acid, dilute sodium hydroxide solution, concentrated sodium hydroxide solution, lime juice, bitter gourd juice, magnesium ribbon, filter paper, sandpaper, blue litmus paper and red litmus paper, wooden splinter, matches, pH paper and pH chart Apparatus: Test tube, dropper, Petri dish and white tile Instruction A
pH value
pH paper
1. Put 10 drops of dilute hydrochloric acid in a Petri dish. Petri 2. Test the substance in the Petri dish with a piece of pH paper (Figure 6.1). dish 3. Determine the pH value by comparing the colour of the pH paper with Dilute hydrochloric acid a pH chart. 4. Record your observation. Figure 6.1 5. Repeat steps 1 to 4 by replacing dilute hydrochloric acid with dilute sodium hydroxide solution. 126
6.1.1
Chapter 6 : Acid and Alkali
B
Taste
1. Taste lime juice followed by bitter gourd juice. Gargle with water after tasting each substance. 2. Record your observations. C
Corrosiveness (Teacher’s demonstration)
1. Put one drop of concentrated hydrochloric acid on a piece of filter paper placed on a white tile (Figure 6.2). 2. Record your observation. 3. Repeat steps 1 and 2 by replacing concentrated hydrochloric acid with concentrated sodium hydroxide solution. D
Effect on blue litmus paper and red litmus paper
1. Place a blue litmus paper and a red litmus paper on a white tile. 2. Put one drop of dilute hydrochloric acid on both litmus papers and record your observations. 3. Repeat steps 1 and 2 by replacing dilute hydrochloric acid with dilute sodium hydroxide solution. E
Reaction with metals
1. Clean a magnesium ribbon with sandpaper. 2. Put the magnesium ribbon into a test tube filled with 5 ml of dilute hydrochloric acid. 3. Close the test tube with your thumb for one minute. 4. Remove your thumb and place a lighted wooden splinter at the mouth of the test tube (Figure 6.3). 5. Record your observation. 6. Repeat steps 1 to 5 by replacing dilute hydrochloric acid with dilute sodium hydroxide solution.
Safety
Precaution
• Carry out this activity in a fume chamber. • Use the acid and alkali in small amounts. • Wear safety goggles.
Concentrated hydrochloric acid
Dropper Filter paper White tile
Figure 6.2
Gas collected
Test tube
Dilute hydrochloric acid
Magnesium ribbon
Burning wooden splinter
Test tube
Dilute hydrochloric acid
Magnesium ribbon
Figure 6.3
Observation Substance
Activity
Acidic
Alkaline
A B C D E
127
Questions 1. What is the pH range of alkalis? 2. Give an inference for your observation in Activity E. 3. Why should the magnesium ribbon be cleaned with sandpaper before using it? 4. Predict the taste of vinegar and neem. 5. Give the operational definition of an acid and an alkali.
After carrying out Activity 6.1, can you identify the properties of acids and alkalis? Table 6.2 summarises the properties of an acid and an alkali. Table 6.2 Properties of an acid and an alkali Acid
Alkali
pH value less than 7
pH value more than 7
Tastes sour
Tastes bitter
Corrosive
Corrosive
Turns blue litmus paper red
Turns red litmus paper blue
Reacts with metals to produce hydrogen gas
Does not react with metals
The Role of Water in Showing the Properties of Acids and Alkalis
Brain You should remember that acids and alkalis show their properties only in the presence of water.
What is the meaning of pH?
Alkali
Acid No change in the colour of blue litmus paper Glacial ethanoic acid
Without water
Teaser
Ethanoic acid in water
No change in the colour of red litmus paper
Blue litmus paper turns red
Solid sodium hydroxide
With water
Without water
Sodium hydroxide in water
Red litmus paper turns blue
With water
Figure 6.4 Acids and alkalis show their properties in the presence of water
Acidic and Alkaline Substances Substances that contain acids are known as acidic substances, whereas substances that contain alkali are known as alkaline substances. Various foods in the kitchen can be classified into acidic and alkaline substances. For example, apples and coffee are acidic substances while baking soda is alkaline. Can you name another alkaline substance found in your kitchen? 128
6.1.2
Chapter 6 : Acid and Alkali
Substances Acidic
Alkaline
Vinegar
Soap
Lemon juice
Toothpaste
Figure 6.5 Examples of acidic and alkaline substances
The characteristic of different substances can be determined using a suitable indicator. An indicator is a colouring or a mixture of different colourings that changes colour based on the substance tested. The colour change observed can be used to determine if a substance is neutral, acidic or alkaline.
Info
Indicator http://www.bbc. co.uk/
Table 6.3 Colour change of various indicators Indicator
Acid
Neutral
Alkali
Phenolphthalein
Colourless
Colourless
Pink
Universal indicator
Red
Green
Blue
Methyl orange
Red
Yellow
Yellow
Blue litmus paper
Red
Blue
Blue
Red litmus paper
Red
Red
Blue
A ctivity 6.2 Aim: To determine acidic and alkaline substances in daily life using various indicators. Materials: Blue litmus paper, red litmus paper, universal indicator, methyl orange, phenolphthalein, fizzy drink, dishwashing liquid, distilled water, syrup and salt water Apparatus: Dropper, test tube, measuring cylinder, pH meter and test tube rack
Note: The colours of substances tested with the universal indicator should be compared with the pH chart.
Instruction 1. Add 2 ml of a fizzy drink, dishwashing liquid, distilled water, syrup and salt water into separate test tubes, then place them in a test tube rack. 2. Test these substances with blue litmus paper and red litmus paper. 3. Record your observations in a table. 4. Repeat steps 1 to 3 by replacing the litmus papers with universal indicator, methyl orange, phenolphthalein and pH meter.
129
Observation Indicator Blue litmus paper and Universal Methyl red litmus indicator orange paper
Substance
Phenolphthalein
pH meter
Acid/ Alkali
Fizzy drink Dishwashing liquid Questions 1. What is the advantage of using universal indicator compared to litmus paper? 2. What is your inference on a substance that has a pH value of 7?
Strength of Acids and Alkalis The pH scale is used to show the strength of acids or alkalis. The range of pH value is between 0 to 14. What is the relationship between the pH value and the strength of an acid and alkali? More acidic pH
0
1
2
3
4
More alkaline
Neutral 5
6
7
8
9
10
11
12
13
14
Figure 6.6 The pH scale
A ctivity 6.3 Aim: To study the relationship between the pH value and the strength of an acid and alkali. Materials: pH paper, 0.1 M hydrochloric acid, sodium hydroxide solution, 0.1 M ethanoic acid, ammonia solution, pH chart and salt solution Apparatus: Measuring cylinder, test tube and test tube rack
Note: Make sure all the solutions used have the same concentration.
Instruction 1. Pour 2 ml of hydrochloric acid into a test tube. 2. Test the substance in the test tube with a pH paper. 3. Observe the colour change of the pH paper and compare it with a pH chart to determine the pH value. 4. Record your observation in a table. 5. Repeat steps 1 to 4 by replacing hydrochloric acid with the other substances. Observation Substance
Hydrochloric Sodium hydroxide acid solution
Ethanoic acid
Ammonia solution
Salt solution
pH value
130
6.1.3
Chapter 6 : Acid and Alkali
Questions 1. Relate the strength of acid to the pH value. 2. Identify the substance which is a: (a) strong acid (d) weak alkali (b) strong alkali (e) neutral solution (c) weak acid 3. Predict the pH value of rain water in an industrial area. Explain your answer.
After carrying out Activity 6.3, we can conclude that the lower the pH value, the stronger the acid; the higher the pH value, the stronger the alkali.
Uses of Acids and Alkalis in Daily Life Acids and alkalis are widely used in our daily lives. For instance, we use vinegar which is acidic in cooking, and detergent which is alkaline for washing clothes. Besides, acids and alkalis are also used in various sectors such as the agricultural, industrial and medical sectors. For example, fertilisers used in agriculture are produced from the reaction between acidic and alkaline substances. Can you name the alkaline substance?
Brain
Teaser
What will happen to crops if the acidity of soil increases?
Photograph 6.2 Ammonia solution is used to produce fertilisers
Let us carry out Activity 6.4 to find out the usage of acids and alkalis in daily life.
A
ctivity
6.4
21
st
Century
Aim: To gather information on the usage of acids and alkalis in daily life. Instruction: 1. Work in groups. 2. Gather information on the usage of acids and alkalis in daily life including agricultural and industrial sectors. 3. Present the finding using a mind map.
6.1.4
131
Kafh Cola
ACID
Tartaric acid
Fizzy drink
Car battery
Pickle
Tartaric acid
Carbonic acid
Sulphuric acid
Vinegar
ALKALI
Soap
Fertiliser
Antacid pills
Potassium hydroxide
Ammonia
Magnesium hydroxide
Detergent
Sodium hydroxide
Photograph 6.3 Uses of acids and alkalis in daily life
Formative Practice
6.1
1. Predict the arrangement of the following substances in decreasing order of pH value. Orange juice
Bitter gourd juice
Hydrochloric acid
Mineral water
2. Explain the reason why the labels of acid and alkali bottles have the symbol as in the diagram below.
3. The colour of liquid X changes from green to red when universal indicator is added. (a) Determine whether liquid X is acidic, neutral or alkaline. (b) Predict the colour of liquid X if a few drops of methyl orange are added into it. 4. Arrange the following substances in increasing order of acid strength. Pineapple juice: pH 4
132
Fresh milk: pH 6
Vinegar: pH 2
Chapter 6 : Acid and Alkali
6.2
Neutralisation
W
hat will happen if an acid is mixed with an alkali? The reaction between an acid and an alkali produces salt and water. This reaction is called neutralisation. During neutralisation, an acid loses its acidity while an alkali loses its alkalinity. The method used to carry out this reaction is called titration. The word equation for this neutralisation reaction is:
Different acids and alkalis produce different salts. For example: Hydrochloric acid
+
Sodium hydroxide
Sodium chloride
+
water
Sulphuric acid
+
Potassium hydroxide
Potassium sulphate
+
water
Nitric acid
+
Sodium hydroxide
Sodium nitrate
+
water
A ctivity
6.5
Aim: To study the neutralisation reaction between hydrochloric acid and sodium hydroxide solution. Materials: Phenolphthalein, 0.5 M hydrochloric acid and 0.5 M sodium hydroxide solution Apparatus: Burette, pipette, conical flask, retort stand with clamp, white tile and filter funnel Instruction 1. Fill 30 ml of hydrochloric acid into a burette using a filter funnel and record the initial reading of the burette. 2. Transfer 25 ml of sodium hydroxide solution into a conical flask using a pipette. 3. Add three drops of phenolphthalein into the conical flask. Set up the apparatus as shown in Figure 6.7. 4. Add the hydrochloric acid from the burette drop by drop into the conical flask while shaking the flask gently. 5. Stop adding the acid when the sodium hydroxide solution changes colour from pink to colourless. 6. Record the final reading of the burette.
Retort stand with clamp
Conical flask
Burette Hydrochloric acid Sodium hydroxide solution + phenolphthalein White tile Figure 6.7
Observation Initial reading of the burette (ml) Final reading of the burette (ml) Volume of hydrochloric acid used (ml)
6.2.1
133
Questions 1. What is the volume of hydrochloric acid required to neutralise 25 ml of sodium hydroxide solution? 2. Write the word equation for the reaction between the acid and alkali in this activity.
Applications of Neutralisation in Daily Life Neutralisation has many applications in our daily lives. Besides, it is also used in the agricultural and industrial sectors.
I’m inhabited by bacteria that produce acid. Luckily, there are toothpastes that contain alkaline substance that can neutralise the acid produced by the bacteria.
Brain Figure 6.8 Application of neutralisation of acid on dental care
Face cleansers which are alkaline will make the facial skin dry. Therefore, acidic toners are used to neutralise the skin.
Teaser
How can alkaline shampoo and acidic hair conditioner be combined into a 2 in 1 shampoo bottle?
Healthy hair has a slightly acidic condition, however, hair shampoos make hair slightly alkaline. Therefore, a mildly acidic hair conditioner can neutralise the residue of the shampoo on hair and make the hair smooth and healthy.
Photograph 6.4 Applications of neutralisation in self-care products 134
6.2.2
Chapter 6 : Acid and Alkali
Acidic soil can be treated by adding slaked lime which is alkaline in order for plants to grow well.
Fabric softeners are acidic, thus they reduce the pH level of fabrics which become alkaline after being washed with detergents.
Fabric Softener
ZILA
Acidic waste substances from factories are treated with alkalis before being discharged into the river. Photograph 6.5 Applications of neutralisation in the agricultural and industrial sectors
Formative Practice
6.2
1. (a) Complete the following equation. Acid + Alkali
+
(b) If sulphuric acid and sodium hydroxide solution are added together, what would be the product? Write down your answer in a word equation. 2. Explain how toothpaste works in cleaning teeth and preventing dental caries. 3. Is hair conditioner important? Explain your answer.
135
136
Methyl orange
Effects on blue litmus paper and red litmus paper
The role of water
Reaction with metals
pH meter
Phenolphthalein
Industrial sector
Universal indicator
Corrosiveness
Taste
Agricultural sector
Uses in daily life
Blue litmus paper and red litmus paper
Indicator
Acid and Alkali
pH Value
Properties
Summary
Titration
Interactive Quiz 6
Daily life applications
Quiz
Neutralisation
Chapter 6 : Acid and Alkali
SELF-REFLECTION After learning this chapter, you are be able to: 6.1 Properties of Acids and Alkalis Define operationally acid and alkali. Explain with examples of acidic and alkaline substances. Demonstrate the technique to determine the strength of acid and alkali based on pH value. Identify the uses of acids and alkalis in daily life. 6.2 Neutralisation Explain the neutralisation reaction. Explain with examples the applications of neutralisation reaction in daily life.
Summative
Practice
6
1. The following is a list of several substances. Malic acid
Formic acid
Potassium hydroxide solution
Based on the list above, answer the following questions. (a) Which substance has the pH value of less than 7? (b) State the substance found in (i) fire ants (ii) green apples (c) Predict your observation if a magnesium ribbon is put in potassium hydroxide solution and tested with a lighted wooden splinter. 2. (a) Shida wants to carry out an activity to determine the pH value of ammonia gas. Based on your knowledge of acid and alkali, explain how Shida can determine the pH value of the ammonia gas. (b) State one advantage of pH paper compared to litmus paper. (c) Grace added two drops of phenolphthalein into colourless solution M. She found that the solution remained colourless. (i) Is solution M acidic? Explain your answer. (ii) Suggest another test that should be carried out to strengthen your answer in (i).
137
3. Figure 1 shows the reactions of blue litmus paper and red litmus paper when tested with three different solutions. (a) Based on your observation, classify the solutions into two groups according to their common characteristics.
P
(b) State two other characteristics of each group that you stated in 3 (a).
Q
R
Figure 1
(c) State one example of daily life substance that has the characteristic as (i) solution P (ii) solution Q 4. Amran was stung by a jellyfish when he was swimming in the sea with his friends. The part of his body stung by the jellyfish became red and swollen. The pain became worse when his friend applied soap and toothpaste on the affected area. (a) Explain why Amran’s pain became worse when applied with soap and toothpaste. (b) Suggest a way to reduce Amran’s pain.
HOTS
Mastery
6
5. (a) Kiran was cleaning the fish she bought from the market. The fishy smell made her feel sick. Suggest one way to remove the fishy smell. (b) How can you neutralise vinegar using sodium hydroxide solution? State the procedure for this activity. 6. A farmer found out that his agricultural land is not fertile. His son carried out simple tests on the soil sample to identify the cause. Table 1 shows the tests carried out and the observations obtained. Table 1
Test
Observation
Soil sample + Baking soda + Water
Gas bubbles are observed
Soil sample + Vinegar
No gas bubbles are observed
(a) Based on the observation for both tests on the soil sample, what can be concluded? (b) Relate your answer in 6 (a) with infertility of the soil. (c) Suggest and explain one way to overcome the farmer’s problem.
138
Energy and Sustainability of Life
3
What is electricity
and magnetism?
What is force? ?
ured How is force meas
rth?
Ea urce of energy on
What is the main so
t How do liquids reac
with heat? s produce
usic instrument Why do different m different sound?
139
Cha
er t p
7
Electricity and Magnetism
How can wind be used to generate electricity? Which energy is needed for vehicles to move? What causes the formation of lightning? Why does the compass always show the north-south direction?
Let’s understand: Electricity The flow of electric current in a series circuit and a parallel circuit Magnetism 140
Chapter 7 : Electricity and Magnetism
Science Blog
SCIENCE BLOG Science Blog
The Electric Eel The electric eel or scientifically known as Electrophorus electricus is a type of freshwater fish found in South America. The length of its body can exceed 8 feet. This fish has around 6 000 special cells known as electrocytes. These cells are their secret weapon that enables the electric eel to discharge electricity up to 600 volts! Electricity that is discharged is used to protect the fish from its predators and to catch smaller fishes. This fish’s eyesight is limited because of its dark and muddy habitat. This causes the fish to use the transmission of electric charges as a guide for direction.
Keywords Electric current
Series circuit
Electric charge
Resistors
Electrostatic
Magnetic field
Ohm’s Law
Magnet
Parallel circuit
Electromagnet
141
7.1
Electricity
D
o you still remember the topic on electricity that you have learned during primary school? Various home appliances such as the washing machine, television, computer and others use electricity to function.
Energy All living things need energy. A moving vehicle, a lighted bulb, and a sleeping cat use energy. What does energy mean? Energy means the ability to do work. Can you state a few daily activities that use energy?
Plants need energy from the Sun to continue living
People use energy to run
Cars need energy from fuel to move
The light from the bulb is produced by energy
Photograph 7.1 Various uses and needs of energy
What is the S.I. unit for energy?
The S.I. unit for energy is joule (J).
142
7.1.1
Chapter 7 : Electricity and Magnetism
Forms of Energy Energy cannot be created nor destroyed but it can exist in various forms. Photograph 7.2 shows various forms of energy that exist around us. Can you give another example for each of the following types of energy?
Sound energy
Gravitational potential energy
Nuclear energy
Kinetic energy
Electrical energy
Elastic potential energy
Light energy
Heat energy
Chemical energy
Photograph 7.2 Various forms of energy
Sources of Energy You have learned various forms of energy that exist. What are the sources used to generate energy? Figure 7.1 shows various sources of energy that exist around us. The Sun
Wind
Wave
Radioactive substance
Geothermal Sources of energy
Water
Brain
Teaser
Does nuclear energy produce radioactive wastes?
Biomass Fossil fuel
Figure 7.1 Various sources of energy 143
21
A ctivity 7.1
st
Century
Aim : To discuss energy. Instruction 1. Work in groups. 2. Discuss: (a) the importance of energy in our daily lives (b) forms of energy (c) sources of energy 3. Use various sources to gather these information. 4. Present your discussion in the form of a multimedia presentation.
Electrostatic Charges Have you ever felt an electric shock when you touched a door knob? Why does this happen? It happens as a result of the transfer of electric charges between our body and the door knob that has static electric charges. These static charges are known as electrostatic charges. Let us carry out Activity 7.2 to show the existence of electrostatic charges on different types of materials.
A ctivity7.2 Aim: To test the existence of electrostatic charges on certain materials. Materials: Balloon, pieces of shredded paper and stream of running tap water Apparatus: Polythene rod, cellulose acetate strip and woollen cloth
Note: Make sure that all the apparatus are dry.
Polythene rod
Instruction 1. Rub a polythene rod with a woollen cloth. 2. Hold the rod close to pieces of shredded paper (Photograph 7.3) and record your observation. 3. Repeat step 1. 4. Hold the rod close to a small stream of running tap water and record your observation. 5. Repeat steps 1 to 4 using a cellulose acetate strip and a balloon to replace the polythene rod.
Pieces of shredded papers Photograph 7.3
Questions 1. Give an inference for your observation. 2. What other methods can be used to test the existence of electrostatic charges on the balloon? Explain the steps taken.
Info 144
Tap Water and Electrostatic Charges https://www.thoughtco.com/bend-waterwith-static-electricity-604268 7.1.2
Chapter 7 : Electricity and Magnetism
Based on your observation in Activity 7.2, how are the electrostatic charges between the objects produced? Electric charges consist of positive charges (proton) and negative charges (electron). The attraction and repulsion between the electric charges shown in Figure 7.2 are known as electrostatic forces. Same charges When two different types of objects are rubbed together, repel each only the electrons are transferred from one object to the other other, whereas the protons do not move. The object that Opposite gains electrons will be negatively charged. The object that charges attract loses electrons will be positively charged. The object that has each other equal number of protons and electrons is known as neutral. Figure 7.2 Properties of electric charges
The number of protons is more than the electrons Positively charged
The number of electrons is more than the protons Negatively charged
The number of protons and electrons is equal Neutral
Figure 7.3 The number of electrons on objects
Look at Figure 7.4 to understand the effect of electrostatic charges on a plastic comb that has been rubbed with a piece of woollen cloth.
Before being rubbed with the woollen cloth
After being rubbed with the woollen cloth
+ – + – + – + – – + – + + –
Neutral comb – – +
+ – + – – + – + – +
Pieces of neutral shredded paper
+ + + + – – – + + + – – – – –
–
+
–
+ – – +
+ + +
–
–
–
The comb rubbed with the woollen cloth will gain electrons from the woollen cloth and will be negatively charged. This enables the comb to attract the pieces of paper because of the force of attraction that exist between the positive charges on the pieces of paper and the negative charges on the comb.
Figure 7.4 Effect of production of electrostatic charges 145
Electroscope
Metal cap
An electroscope is a device used to detect the existence of electric charges on an object. Neutral strip –+ –+–+ +– +– – + – + – +
– + – + – +
Positively charged strip ++ ++ + – – –+ – +– +–
Negatively charged strip
Gold leaf
––– – –– +
e–
+ + – + – + – –
+ + + ++ +
(a)
Insulator
e–
+ – + – + – –
(b)
Photograph 7.4 An electroscope
The gold leaf does not The gold leaf diverges because the diverge because the same charges repel each other. positive and negative charges are attracted to one another. Figure 7.5 How the electroscope works
Today
in
History
The first gold leaf electroscope was invented by a physicist, Abraham Bennet in 1787.
The further the divergence of the gold leaf, the higher the quantity of electrostatic charges accumulated.
Examples of Electrostatic in Our Daily Life The occurrence of lightning is one of the phenomena that is related to electrostatic charges. The friction between clouds and air causes the clouds to be charged with electric charges. Lightning is a result of the force of attraction that exists between the positive charges on the ground and the negative charges in the clouds. The upper part of the cloud is positively charged
The bottom part of the cloud is negatively charged
Science Lightning conductor
+ + + + + Cloud + + + + + + + + + + + – – – – –– – – – – – –– –
Lightning
The negative charges in the clouds are attracted to the positive charges on the surface of the earth
+ + + + + + + Earth + + + + + + +
The lightning conductor is installed at buildings to provide a path for the electric charges to flow into the ground. This method protects the building from being struck by lightning.
Figure 7.6 Lightning 146
7.1.3
Chapter 7 : Electricity and Magnetism
Science Simulation of lightning can be carried out in the school laboratory by using a Van de Graaff generator or Wimhurst machine. Carry out Activity 7.3 to observe the simulation of lightning.
A
ctivity
Wimhurst machine is a device for generating high voltages.
21
7.3
st
Century
Aim: To carry out a simulation of lightning formation by using the Van de Graaff generator. Apparatus: Van de Graaff generator Instruction 1. Switch on the Van de Graaff generator. 2. After a few minutes, move the metal sphere closer to the dome and record your observation. Questions 1. What is your observation in this activity? 2. What will happen if the metal cap of an electroscope is brought closer to the dome of the Van de Graaff generator?
Photograph 7.5
Solving Daily Life Problems Involving Electrostatic I cleaned this TV screen two days ago. Its dusty again! The TV screen becomes dusty quickly because the negative charges on the dust are attracted to the positive charges on the TV screen. Use a microfibre cloth, a type of antielectrostatic material so that it does not become dusty too quickly.
A ctivity
7.4
STEM
21
st
Century
Aim: To gather information and solve daily life problems involving electrostatic. Instruction 1. Work in groups. 2. Gather information on the following problems that involves electrostatic. Discuss how to solve them. (a) The choice of fabric to be worn in hot weather (b) Safe shelters during a thunderstorm (use Faraday’s cage concept) 3. Share your findings with the class. 147
Electric Current Electrical appliances require electric charges to operate. Energy that is needed for the electric charges to flow can be generated from sources such as electrical generators, dry cells and solar cells. What is the relationship between electric charges and electric current? Photograph 7.6 Dry cells
A ctivity 7.5 Aim: To study the relationship between electric charges and electric current. Apparatus: Van de Graaff generator, galvanometer and connecting wire
Safety
Precaution
Make sure all the apparatus
Instruction are dry and neutral. 1. Set up the apparatus as shown in Figure 7.7. 2. Switch on the Van de Graaff generator and observe the pointer on the galvanometer. Dome of Van de Graaff generator
Science Galvanometer
earthed
Figure 7.7
A galvanometer is used to detect very small electric currents.
Questions 1. What happens to the galvanometer’s pointer? Explain. 2. How do you show the existence of electric charges on the dome of the generator? 3. State the meaning of electric current.
The deflection of the galvanometer’s pointer indicates the flow of the electric current. Electric current can be defined as the rate of flow of electric charges through a conductor.
Measuring the Quantity of Electricity The flow of electric current can be measured by using an ammeter. You have learned in Form One that the S.I. unit for electric current is ampere (A). The voltage is the potential difference between two points that can be measured in volt (V) by using a voltmeter.
148
Photograph 7.7 Voltmeter
7.1.4 7.1.5
Chapter 7 : Electricity and Magnetism
A ctivity 7.6 Aim: To measure the current and voltage by using a suitable measuring apparatus. Apparatus: Ammeter, voltmeter, connecting wire, switch, dry cell, crocodile clip, bulb and dry cell holder A
Ammeter
Measuring current using an ammeter
Instruction 1. Connect the circuit as shown in Photograph 7.8 using one dry cell. 2. Turn on the switch and record the reading of the ammeter. Observe the brightness of the bulb. 3. Record your observations. 4. Repeat steps 1 to 3 using two dry cells. B
Connecting wire
Switch
Dry cell Crocodile clip Dry cell holder
Bulb Photograph 7.8
Measuring the voltage using a voltmeter
Safety
Precaution
The voltmeter must be connected parallel to the bulb in order to measure the voltage.
Switch
Instruction Voltmeter 1. Connect the circuit as shown in Photograph 7.9 using one dry cell. 2. Turn on the switch and record the reading of the voltmeter. Observe the brightness of the bulb. 3. Record your observations. 4. Repeat steps 1 to 3 using two dry cells.
Dry cell Crocodile clip Dry cell holder
Bulb Photograph 7.9
Observation Activity A B
Connecting wire
Number of dry cells
Reading of ammeter / A
Reading of voltmeter / V
Brightness of bulb
1 2 1 2
Questions 1. What is the relationship between the electrical current and the increase in the number of dry cells? 2. What is the relationship between the voltage and the increase in the number of dry cells? 3. Give an inference for the brightness of bulb in Activity A. 4. What is the relationship between the voltage, electric current and the brightness of the bulb?
Science Multimeter can be used to measure current and voltage. 149
The Relationship between Current, Voltage and Resistance The ability of a conductor to limit or resist the flow of electric current is known as resistance. The unit for measuring resistance is ohm (Ω). A fixed resistor has resistance that cannot be adjusted whereas a variable resistor or rheostat has resistance that can be adjusted. Current, voltage and resistance are three electrical quantities that are closely related to one another in a circuit. The changes in magnitude of one of the electrical quantities will have an effect in the magnitude of the other quantities. Let us carry out Experiment 7.1 to study the relationship between current, voltage and resistance.
Experiment
7.1
Aim: To study the effects of changes in resistance and voltage on electric current. A
The effect of changes in resistance on electric current
Problem statement: What is the effect of changes in resistance on electric current? Hypothesis: The higher the resistance, the smaller the current flow. Variables: (a) Constant variable: Number of dry cells (b) Manipulated variable: The length of the nichrome wire (c) Responding variable: Reading of the ammeter Material: Nichrome wire (60 cm) Apparatus: Ammeter, metre rule, dry cell holder, dry cell, thumbtack, crocodile clip, jockey and connecting wire Procedure: 1. Fix a nichrome wire to both ends of a metre rule. 2. Set up the apparatus as shown in Photograph 7.10. 3. Place the jockey where the length of the nichrome wire is 20 cm. Record the reading of the ammeter. 4. Repeat step 3 by increasing the length of the nichrome wire to 30 cm, 40 cm, 50 cm and 60 cm. 5. Record the ammeter readings in a table for each length of the nichrome wire used. 6. Plot a graph of current against the length of nichrome wire. Ammeter Crocodile clip Dry cells
Connecting wire
Dry cell holder
Thumbtack Metre rule
150
Jockey
The length of nichrome wire Photograph 7.10
Nichrome wire
7.1.6
Chapter 7 : Electricity and Magnetism
Observation: Length of nichrome wire (cm)
Reading of ammeter (A)
20 30 Conclusion: Is the hypothesis accepted? Give your reasons. Questions 1. What is the relationship between the length of the nichrome wire and resistance? 2. What is the relationship between the length of the nichrome wire and the current that flows in the circuit? 3. What is the relationship between resistance and electric current? B
The effect of changes in voltage on electric current
Problem statement: What is the effect of changes in voltage on current? Hypothesis: The higher the voltage, the larger the current flow Variables: Voltmeter (a) Constant variable : Nichrome wire of 10 cm length Ammeter (b) Manipulated variable : Number of dry cells Crocodile (c) Responding variable : Reading of the ammeter clip Apparatus: Ammeter, voltmeter, connecting wire, nichrome wire of 10 cm length, dry cell and crocodile clip
Connecting wire
Procedure: 1. Set up the circuit as shown in Photograph 7.11 using one dry cell. 2. Record the reading on the ammeter and voltmeter. 3. Record your observations in a table. 4. Repeat steps 1 to 3 using two, three and four dry cells. 5. Plot a graph of current against voltage.
Nichrome wire
Dry cell
Photograph 7.11
Dry cell holder
Observation: Number of dry cells
1
2
3
4
Reading of ammeter (A) Reading of voltmeter (V) Conclusion: Is the hypothesis accepted? Give your reasons. Questions 1. What is the relationship between the number of dry cells and the reading of voltmeter? 2. What is the relationship between voltage and electric current?
151
Experiment 7.1 shows that the amount of current flowing through the circuit decreases as the resistance increases. Besides, we can also observe that when a higher voltage flows through the circuit, the amount of current flowing through the circuit also increases. Science The relationship between the current, I, the voltage, V and the resistance, R is known as the Ohm’s Law. The relationship among these three electrical quantities can be written as: V = IR Ohm’s Law states that the electric current that flows through a conductor is directly proportional to the voltage across two ends of the conductor, provided the temperature and other physical situations remain unchanged.
Ohm’s Law Triangle can be used to memorise the Ohm’s Law. Put your finger over the quantity that you are looking for. Then, multiply or divide the other two quantities that are given. V I R V I R
Formative Practice
7.1
I=V – R
V I R
V=I R
V I R
R=V – I
1. State the forms of energy that exists in each of the following situations. (a) Boiling water (b) A chicken running (c) Compressed spring 2.
As the clouds move, a lot of electric charges are accumulated by the clouds.
Based on the statement above, explain the occurrence of lightning. 3. What is the resistance of a car light bulb that conducts 0.025 A current when connected to a 12 V car accumulator? Is the current in the bulb steady?
7.2
E
Flow of Electric Current in a Series Circuit and Parallel Circuit
lectric current requires a complete path which enables it to flow. This path is known as an electric circuit.
Electrical Circuit Components A complete electric circuit is made up of various electrical components which are represented by symbols. These symbols are used to draw circuit diagrams.
152
7.2.1
Chapter 7 : Electricity and Magnetism Table 7.1 Electrical components and their symbols Electrical component
Symbol
Electrical component
Switch
Bulb
Dry cell
Resistor
Voltmeter
V
Fuse
Galvanometer
G
Variable resistor
Ammeter
A
Symbol
or
Series Circuit and Parallel Circuit Why are all the bulbs lighted up except for one? The bulbs are connected in parallel circuit.
An electric circuit can be connected in series or parallel. A series circuit is made up of electrical components that are connected one after another where the current flows through in a single path (Figure 7.8). A parallel circuit is separated into several different paths of electrical circuit and each parallel path has electrical components (Figure 7.9).
Figure 7.8 Series circuit
Figure 7.9 Parallel circuit
153
Current, Voltage and Resistance in a Series Circuit Is the current that flows through each electrical component in a series circuit the same? Carry out Activity 7.7 to study the current, voltage and resistance in a series circuit.
A ctivity 7.7 Aim: To study current, voltage and resistance in a series circuit.
I A
Apparatus: Dry cell holder, connecting wire, bulb (1.5 V), dry cell, switch, ammeter and voltmeter Instruction 1. Set up a series circuit as shown in Figure 7.10 (a). 2. Turn on the switch and measure the current that flows through bulb M. Measure the current that flows through bulb N by placing the ammeter between M and N as shown in Figure 7.10 (b). 3. Measure the current that flows through bulb M and N by setting up the circuit as shown in Figure 7.10 (c). 4. Set up the voltmeter across bulb M, followed by bulb N as shown in Figure 7.10 (d) to measure the voltage reading across the bulb. 5. Set up the voltmeter as shown in Figure 7.10 (e) to measure the voltage across two bulbs. 6. Calculate the resistance for each bulb separately and also for both the bulbs using Ohm’s Law. 7. Record all the readings in a table. Questions 1. What is your conclusion on the current flow through the series circuit? 2. What will happen to the bulbs in the series circuit if one of the bulbs is removed?
M
N (a)
I1 A
M
N
(b)
M
I2 A
N (c)
A
V1
M V
N
(d)
M
V
V
V2
N V (e)
Figure 7.10
After carrying out Activity 7.7, you will notice that the current that flows through each bulb is the same but the voltage is the sum of the voltages across each bulb. Effective resistance, R is the total resistance across the components. We can conclude that: Current, I = I1 = I2
154
Voltage, V = V1 + V2
Resistance, R = R1 + R2
Chapter 7 : Electricity and Magnetism Table 7.2 Advantages and disadvantages of a series circuit Advantages • Every component in the circuit receives the same amount of current. • Every component is controlled by the same switch. • Increase in voltage supplies more electric current.
Disadvantages • When one of the electrical appliances is damaged, other electrical appliances cease to function. • Adding more electrical appliances increases resistance and decreases the flow of the current. • Each electrical appliance cannot be switched off individually.
Current, Voltage and Resistance in a Parallel Circuit Current, voltage and resistance in a parallel circuit is different from a series circuit. Carry out Activity 7.8 to investigate the current, voltage and resistance in a parallel circuit.
A ctivity 7.8 Aim: To study current, voltage and resistance in a parallel circuit. Apparatus: Dry cell holder, connecting wire, switch, bulb (1.5 V), dry cell, ammeter and voltmeter Instruction 1. Set up a parallel circuit as shown in Figure 7.11 (a). 2. Turn on the switch and measure the current that flows through bulb M. Measure the current that flows through bulb N by changing the position of the ammeter. 3. Measure the electric current that flows through both the bulbs, M and N by setting up a circuit as shown in Figure 7.11 (b). 4. Fix the voltmeter across bulb M followed by bulb N as shown in Figure 7.11 (c) to measure the voltage across the bulbs. 5. Fix the voltmeter as shown in Figure 7.11 (d) to measure the voltage across two bulbs. 6. Calculate the resistance for each bulb separately and for both the bulbs using Ohm’s Law. 7. Record all the readings in a table. Questions 1. Is the value of voltage different for bulb M and N? 2. List out the advantages and disadvantages of a parallel circuit.
I1 A I2 A
M N (a)
M A I N (b)
V
V1
M V N
V2
(c)
V M
V
N (d)
Figure 7.11
155
Voltage, V that flows across each resistor in a parallel circuit is the same as the voltage that flows across the dry cell. However, the current, I that flows in a parallel circuit is actually the total amount of current that flows through each resistor. Therefore, the current and the voltage can be concluded as: Current, I = I1 + I2 Voltage, V = V1 = V2 Effective resistance, R can be calculated using the following formula:
1 1 1 = + R R1 R2
Table 7.3 Advantages and disadvantages of a parallel circuit Advantages
Disadvantages
• Every electrical appliance can be switched on or off separately. • The increase in the number of electrical appliances does not affect the function of other appliances in the same circuit.
• The voltage for every electrical appliance cannot be adjusted because the voltage is the same as the source of voltage.
The electrical wiring system in our homes is connected in parallel. For example, all the lights at home are connected in parallel to ensure every light gets the same voltage from its main power supply. The current that flows from the main power supply to the circuit is controlled by a distribution panel (Photograph 7.12). Photograph 7.12 Distribution panel
Numerical Problems Related to Current, Voltage and Resistance in Series Circuit and Parallel Circuit 6V 1. Two resistors, R1 and R2 are connected in series in a circuit as shown in Figure 7.12. Calculate: (a) the effective resistance, R (b) the current, I in the circuit (c) the voltage, V1 and V2
A R1 = 2 V
R2 = 2 V
V1
V2
Figure 7.12
Solution: (a) Effective resistance, R R= R1 + R2 R=2Ω+2Ω R=4Ω
156
(b) Current, I V I= R 6V = 4Ω = 1.5 A
(c) V1 = IR1 = 1.5 A× 2 Ω =3V V2 = IR2 = 1.5 A× 2 Ω =3V
Chapter 7 : Electricity and Magnetism
2. Two resistors, R1 and R2 are connected in parallel in a circuit as shown in Figure 7.13. Calculate: (a) the effective resistance, R (b) the voltage, V (c) the current, I in the circuit
6V
A
I
V1
Solution: (a) Effective resistance, R 1 1 1 = + R R1 R2 1 1 1 = + R 2Ω 2Ω 1 =1Ω R R=1Ω
(b) Voltage, V Voltage across each resistor in a parallel circuit is the same, that is 6 V. (c) Current, I V I1 = 1 R1 6V = 2Ω =3A
I1
R1 = 2 V
I2
R2 = 2 V
V2
V2 R2 6V = 2Ω =3A
Figure 7.13
I2 =
I = I1 + I2 =3A+3A =6A
Science V + – I
R
e–
• Direction of electron flow is from the negative terminal to the positive terminal of an electrical source. • Direction of current flow is from the positive terminal to the negative terminal of an electrical source.
Formative Practice
7.2
1. Draw a parallel circuit using three bulbs, a dry cell, a switch and several connecting wires. 2. Based on Figure 1, calculate: (a) the effective resistance (b) the current in the circuit (c) the voltage across each resistor 3. Based on Figure 2, calculate: (a) the effective resistance (b) the voltage (c) the current flowing through each resistor
1V
3V
5V
9V Figure 1 4V 3V 6V Figure 2
157
7.3
Magnetism
D
o you know what causes button magnets to stick to a whiteboard? These button magnets have pieces of magnet attached to them to enable them to stick on a whiteboard surface (Photograph 7.13). Magnets exist naturally in the form of lodestones. However, man-made magnets, made of materials such as iron, steel, cobalt and nickel, are widely used in our everyday life. Photograph 7.13 Button magnets on whiteboard
Properties of a Magnet You might have already known one of the properties of a magnet, that it only attracts magnetic materials. Do magnets have other properties? Let us learn its properties (Figure 7.14).
Has poles (north pole and south pole)
Attracts magnetic materials Properties of a magnet Like poles repel, unlike poles attract
Freely suspended magnet shows north-south direction
Figure 7.14 Properties of a magnet
Magnetic Field Photograph 7.14 shows only steel balls that are closer to the magnet are attracted by the magnet. The area around the magnet with magnetic force is known as magnetic field.
Photograph 7.14 Magnet and steel balls 158
7.3.1
Chapter 7 : Electricity and Magnetism
A ctivity 7.9 Aim: To study the pattern of a magnetic field. Materials: Iron filings and a piece of thin card
Iron filings
Apparatus: Bar magnet, horseshoe magnet, magnadur magnet, compass and drawing paper
Card
Photograph 7.15 Instruction 1. Sprinkle some iron filings evenly on a thin piece of card. (Photograph 7.15). 2. Place the card on a piece of bar magnet (Photograph 7.16) Card and tap the card gently until a pattern is formed. 3. Draw the pattern that is formed. Bar 4. Arrange four compasses and a bar magnet on the piece of magnet drawing paper as shown in Figure 7.15. Photograph 7.16 5. Mark the direction of the compass needle on the pattern that you have already drawn in step 3. 6. Repeat steps 1 to 5 by replacing the bar magnet with a horseshoe magnet and magnadur magnet. Bar Compass magnet Questions 1. Which part of the magnet can you see the most magnetic field N S lines? 2. What is the direction of the magnetic field lines? 3. What is the relationship between the magnetic field lines and the Figure 7.15 strength of the magnetic field?
You have observed different patterns of magnetic field produced by the magnetic field lines. These magnetic field lines have several characteristics. The magnetic field lines begin from the north pole and end at the south pole.
The magnetic field lines are closer to one another where the magnetic field is stronger.
Brain
Teaser
Does a magnet broken into two pieces still have two poles?
The magnetic field lines never meet or cross.
N
S
Science A magnetic field between two like poles will produce a neutral region (X ) which is free from the effect of any magnetic force.
N
X
N
Figure 7.16 Characteristics of magnetic field lines 159
Electromagnet You have studied electric current in 7.1. Do you know that electric current has magnetic effects? An electromagnet is a type of magnet that has temporary magnetic effect when electric current flows through it. The electric bell is an object that uses electromagnet (Photograph 7.17).
A ctivity 7.10
Photograph 7.17 Electric bell
Aim: To study the pattern and direction of the magnetic field produced by the electric current that flows through different conductors. Materials: Straight wire, coiled wire, thin cardboard, solenoid and iron filings Apparatus: Compass, retort stand with clamp, power supply (D.C. 3 V), connecting wire and crocodile clip Instruction 1. Set up the apparatus as shown in Figure 7.17. 2. Sprinkle some iron filings evenly on the white cardboard. Straight Start the power supply and tap the cardboard gently until wire a magnetic field pattern is formed. 3. Stop the power supply and sketch the magnetic field pattern that has been formed. 4. Place four compasses around the straight wire as shown in Figure 7.18. 5. Restart the power supply and observe the direction of the needle of the compasses. D.C. power 6. Stop the power supply. Mark the direction of the current supply flow and the direction of the magnetic field in the pattern you have drawn in step 3. 7. Reverse the direction of the current flow and observe the pattern and the direction of the magnetic field again. 8. Repeat steps 1 to 7 by replacing the straight wire with coiled wire and solenoid.
White cardboard
Retort stand with clamp
Iron filings Figure 7.17 Compass
Straight wire Figure 7.18
Questions 1. What is the purpose of using the iron filings and compass in this activity? 2. Are the magnetic field patterns for all three conductors similar? 3. What can you observe in the magnetic field when the direction of the electric current is reversed?
The pattern of the magnetic field depends on the shape of the conductor used. For example, the magnetic field lines produced by a straight wire and a coiled wire are concentric circles. Magnetic field lines are closer where the magnetic field is stronger. The strength of the magnetic field reduces as it moves away from the centre of the conductor. The pattern of the magnetic field produced is not affected by the direction of the current that flows through the conductor. The direction of the magnetic field is determined by the direction of the electric current. The right-hand grip rule determines the direction of the magnetic field of the current flow in a straight wire (Figure 7.19). 160
Direction of current Direction of magnetic field
Straight wire
Figure 7.19 Right-hand grip rule
7.3.2
Chapter 7 : Electricity and Magnetism
Science Direction of current
Straight wire
Straight wire
Direction of current
Coiled wire
Current out
Solenoid polarity can be determined by observing the direction of the current flow. The current that flows in the anti-clockwise direction is the north pole, whereas the current that flows clockwise is the south pole.
Current in
Solenoid
Figure 7.20 Pattern and direction of magnetic fields produced by conductors
Experiment 7.2 Aim: To study the factors that influence the strength of the magnetic field. A
The relationship between the current that flows and strength of the magnetic field
Problem statement: Does the current flow affect the strength of the magnetic field? Hypothesis: The larger the current that flows through a conductor, the stronger the magnetic field. Variable: (a) Constant variable : The number of turns of the coil (b) Manipulated variable: Current (c) Responding variable : Number of pins attracted Materials: Pin, iron rod and copper wire Apparatus: D.C. power supply, ammeter, rheostat, Petri dish and retort stand with clamp
Conclusion: Is the hypothesis accepted? Give your reasons.
7.3.3
Iron rod
Ammeter
Procedure: 1. Set up the apparatus as shown in Figure 7.21 with 10 coils of copper wire around the iron rod. 2. Turn on the power supply and adjust the rheostat to obtain 0.5 A of current. 3. Replace the Petri dish containing pins with an empty Petri dish. 4. Turn off the power supply to let all the pins to fall back into the empty Petri dish. 5. Count the number of pins attracted by the iron rod. 6. Repeat steps 1 to 5 using 1.0 A, 1.5 A, 2.0 A and 2.5 A of current. Record your observations.
Retort stand with clamp
Copper wire A
Pins Petri dish Rheostat
Switch D.C. power supply
Figure 7.21
161
B
The relationship between the number of turns of a coil and the strength of the magnetic field
Problem statement: Does the number of turns of a coil affect the magnetic field? Hypothesis: The more the number of turns of a coil, the stronger the magnetic field. Variables: (a) Constant variable: Current (b) Manipulated variable : Number of coils (c) Responding variable : Number of pins attracted Procedure: 1. Set up the apparatus as shown in Figure 7.21 with 10 coils of copper wire coiled around an iron rod. 2. Turn on the power supply. 3. Replace the Petri dish containing pins with an empty Petri dish. 4. Turn off the power supply so that all the pins drop back into the empty Petri dish. 5. Count the number of pins attracted by the iron rod. 6. Repeat steps 1 to 5 using 20, 30, 40 and 50 turns of copper wire on the iron rod. 7. Record your observations. Conclusion: Is the hypothesis accepted? Give your reasons.
Application of Magnets and Electromagnets in Daily Life The needle of a compass uses a magnet to show the direction of the poles.
Credit cards and debit cards have an electromagnetic strip that stores information.
The magnetic lock on doors uses an electromagnet to lock the doors automatically.
Photograph 7.18 Uses of magnets and electromagnets in daily life
Formative Practice
7.3 P
1. What is a magnetic field? Iron 2. Figure 1 shows an iron nail coiled with insulated copper wire nail connected to a dry cell of 1.5 V. Copper (a) What happens when the switch is turned on? wire (b) Mark the direction of the current flow in the copper wire around the iron nail. (c) State the poles of the magnetic field at P and Q. (d) What happens to the strength of the magnetic field if another Q dry cell of 1.5 V is added? 3. State True or False for the following statements. (a) If an object is attracted to magnet, the object is a magnetic material. (b) A straight wire produces magnetic field lines in the shape of concentric circles. 162
Dry cell
Switch
Figure 1
Existence of electrostatic charges Examples of electrostatic in daily life Solving daily life problems
Forms of energy
Sources of energy
Electrostatic charges
Importance of energy
Energy
Summary
1 = 1 + 1 R R1 R2
I = I 1 + I2
I = I 1 = I2 R = R1 + R2
V = V1 = V2
Parallel circuit
V = V1 + V2
Series circuit
Electric circuit
Electricity and Magnetism
V = IR
Ohm’s Law
Quiz
Uses of electromagnets in daily life
Uses of magnets in daily life
Interactive Quiz 7
The strength of the magnetic field
Patterns and directions of magnetic field
Electromagnet
Patterns and directions of the magnetic field
Characteristics of magnets
Magnet
Magnetism
Chapter 7 : Electricity and Magnetism
163
SELF-REFLECTION After learning this chapter, you are able to: 7.1 Electricity Describe and communicate about energy. Explain and communicate the existence of electrostatic charges. Explain with examples electrostatic in daily life. Draw a conclusion that the flow of charges produces electric current. Characterise current, voltage and resistance, and their units. Draw a conclusion on the relationship between current, voltage and resistance. 7.2 The Flow of Electric Current in a Series Circuit and Parallel Circuit Elaborate and communicate about the flow of electric current in series circuit and parallel circuit. 7.3 Magnetism Draw a conclusion about the characteristics of a magnet. Describe and communicate about electromagnets. Carry out an experiment and communicate the uses of magnets and electromagnets in daily life.
Summative
Practice
7
1. Tick (3) the correct statement about electrostatic charges. (a) Earthing causes positive charges to flow from the object to the ground. (b) Similar types of electric charges attract one another. (c) An electroscope is used to determine the presence of electrostatic charges. 2. Imran’s office floor is covered with a nylon carpet. (a) What is the effect of electrostatic charges on Imran if he touches an iron chair? Explain your answer. (b) Suggest a method to overcome the effect of the electrostatic charges mentioned in 2 (a). 3. (a) Why doesn’t a Van de Graaff generator function properly in damp weather? (b) Why is the shock from the Van de Graaff generator not as dangerous as the electric shock from a domestic power supply?
164
Chapter 7 : Electricity and Magnetism
4. Complete the following crossword puzzle regarding electricity. (e) (d)
P
Across (b)
allows the electric current to flow through it. (d) A circuit connected in has the same voltage across the bulb.
E
Down
(a)
(a)
is the quantity of electricity that is measured by the ammeter. (c) The unit for resistance is (e) resists the electric current from flowing through a conductor.
(c) (b)
C
O
R
12 V
5. What is the most suitable circuit to be used in a fire alarm system? Explain your answer. 6. Figure 1 shows a parallel electric circuit. Calculate the value of current A1, A2 and the voltage V1, V2 that is not stated.
A1 1.2 A
10 V
2.4 A
V1 A2
10 V V2
Figure 1
HOTS
Mastery
7
7. Why does the copper coil in the electromagnet used in lifting scrap metals (Photograph 1) have many turns?
Copper coil Photograph 1
165
Cha
Cha
er t p
8
er pt
Force and Motion
All daily activities involve force. We need force to produce motion. What is the meaning of force? What is the effect of force on daily activities?
Let’s understand: Force Effects of force 166
Chapter 8 : Force and Motion
Science Blog
SCIENCE BLOG Force is All Around Us Force is an important part of our lives. When you walk or run, chew food or lift objects, you are applying force. You cannot see force but you can feel its effect. Have you ever taken part in football matches or tug-of-war? All these activities require a pulling or pushing force. When playing football, you kick the ball using a pushing force while in tug-of-war, both teams pull hard on opposite ends of the rope to win.
Keywords Force
Frictional force
Direction
Weight
Gravitational force
Moment of force
Elastic force
Pressure
Buoyant force
167
8.1
Force
W
hat is force?
Pulling
Force is a pull or a push upon an object. Almost all daily activities involve force such as opening a can of food, pressing a switch and opening a door. Force may exist in various forms such as gravitational force, weight, normal force, frictional force, elastic force and buoyant force. Let us carry out Activity 8.1 to show the presence of different types of forces. Pushing
Photograph 8.1 Force is used to open a can of food and press a switch
A ctivity 8.1 Aim: To investigate the presence of different types of forces. Materials: Ball, wooden block, sandpaper and water Apparatus: Spring, retort stand with clamp, 50 g weight, beaker and metre rule A Instruction 1. Throw a ball up in the air (Figure 8.1). 2. Observe whether the ball keeps going up or falls down. Figure 8.1
168
8.1.1
Chapter 8 : Force and Motion
B Instruction 1. Place a wooden block on a table. Why does the wooden block remain in its position? 2. Then, push the wooden block (Figure 8.2 (a)). 3. Repeat step 2 by pushing the same wooden block on a sandpaper (Figure 8.2 (b)). 4. Compare the difficulty of pushing the wooden block on the table and on the sandpaper. Wooden block
Wooden block
Sandpaper
Push
Push
(a) Push the wooden block on a table
(b) Push the wooden block on a sandpaper Figure 8.2
C Instruction 1. Hang a spring on a retort stand. 2. Hang a 50 g weight at the end of the spring (Figure 8.3). 3. Observe the change in the length of the spring. 4. Remove the weight and observe the change in the length of the spring.
Retort stand with clamp
Spring Metre rule
50 g weight Figure 8.3
D Instruction 1. Place a wooden block on the surface of the water in a beaker (Figure 8.4). 2. Press the wooden block to the bottom of the beaker and release it. 3. Observe what happens to the wooden block.
Wooden block Water
Questions 1. Identify the forces involved in Activities A, B, C and D. 2. What is the type of force acting on stationary objects? 3. What is the type of force that resists the motion of objects?
Beaker
Figure 8.4
169
Types of Forces
Gravitational force is the force that points towards the centre of the Earth. This force causes all objects that are thrown upwards to fall back to Earth.
Frictional force is the force that resists movement between two surfaces that are in contact with each other.
Normal force is the force produced when an object is in contact with a surface.
Frictional force acts in the opposite direction of motion.
Normal force
Direction of motion
Types of forces
Weight
Frictional force
The weight of an object is defined as the gravitational force acting on it.
Buoyant force is the thrust force acting on an object that is floating on the surface of a fluid.
Elastic force exists when a material is stretched or compressed. Buoyant force
Figure 8.5 Types of forces 170
Chapter 8 : Force and Motion
Characteristics of Force Force is a vector quantity that has magnitude and direction. Magnitude is the quantity or value of a measurement. Point of application of force
Force = 10 N
Photograph 8.2 shows a pushing force with a magnitude of 10 N acting on a box. The direction of the force is as shown by the arrow and the point of application of the force is the hand that exerts the pushing force onto the box.
Photograph 8.2 Force acting on a box that is pushed
Force 15 N
Figure 8.6 shows a hammer being used to remove a nail from the surface of a table. The force acting on the hammer has a magnitude of 15 N and its direction is as shown by the arrow. The point of application of force is at the head of the hammer, which is the area where the applied force is concentrated.
Hammer
Nail
Wooden block
Point of application of force
Table
Figure 8.6 Force acting when removing a nail using a hammer
Measurement of Force
Today
in
History
Force is measured in newton (N), which is named after Sir Issac Newton, the scientist and mathematician who discovered gravitational force.
Teacher, how do we measure force? Do we use a metre rule? No, we measure force by using a spring balance. A spring balance operates based on the principle of spring extension. The magnitude of the force is obtained by reading the scale on the balance. Spring balance
8.1.2
171
Unit of Force The S.I. unit of force is newton (N). The weight of an object is the gravitational force acting on the object. On Earth, an object with a mass of 100 g has a weight of 1 N. Therefore, an object with a mass of 1 kg has a weight of 10 N.
A ctivity 8.2 Aim: To measure force. Materials: Weight (50 g), string, sandpaper and wooden block Apparatus: Retort stand with clamp and spring balance Instruction A
Spring balance
Weight of object
1. Hang a 50 g weight at the end of a spring balance (Photograph 8.3). 2. Record the reading of the spring balance. 3. Add up to five weights and record the reading of the spring balance. Questions 1. What is the physical quantity measured by the spring balance? 2. What is the unit of the physical quantity for your answer in question 1? 3. What happens to the reading of the spring balance when the number of weights is increased? Explain your answer. B
50 g weight
Photograph 8.3
Frictional force
1. Set up the apparatus as shown in Photograph 8.4. 2. Pull the spring balance until the wooden block starts to move and record the reading of the spring balance. 3. Repeat this activity by pulling the wooden block on a sandpaper. Wooden block String
Spring balance Pull
Photograph 8.4
Questions 1. The wooden block moves only when enough pulling force acts on it. What type of force is resisting the movement of the wooden block? 2. State the difference in the reading of the spring balance when the wooden block is pulled on the table and when it is pulled on the sandpaper. What is the force involved that causes the difference between the readings of the two spring balances?
172
8.1.3
Chapter 8 : Force and Motion
Action-Reaction Pair Observe the objects in Photograph 8.5. Why do these objects remain stationary? What are the forces acting on these objects?
Photograph 8.5 Car, book and apple in a stationary state
same
magnitude There are three different situations to explain this concept. Situation 1
An object that remains on a table
A book that remains still on a table experiences gravitational force known as weight. At the same time, a reaction force called normal force will exist in the opposite direction. The book remains still on the table because the magnitude of the weight (action force) is the same as the normal force (reaction force) (Figure 8.7).
Situation 2
Normal force (Reaction force) Weight (Action force)
Figure 8.7 Book that remains on a table
An object that floats on water
A wooden block that floats on water experiences a gravitational force known as weight. At the same time, a reaction force called buoyant force will exist in the opposite direction. Objects can float on water because the magnitude of the weight (action force) is the same as the buoyant force (reaction force)(Figure 8.8).
Buoyant force (Reaction force)
Weight (Action force)
Figure 8.8 Wooden block that floats on water 8.1.4
173
Situation 3 Two trolleys in contact with each other and launched with a spring mechanism will move at same distance but in the opposite direction.
Action force
First trolley
When two trolleys are pushed towards each other as in Figure 8.9 (a), the first trolley with the spring will exert an elastic force on the second trolley (action force) and at the same time, the second trolley will exert an elastic force of the same magnitude but in the opposite direction (reaction force). When the two trolleys that were initially touching each other are launched as in Figure 8.9 (b), they will move at the same distance but in the opposite direction.
Formative Practice
Reaction force
Second trolley
Compressed spring
(a) Reaction force
First trolley
Action force
(b)
Second trolley
Figure 8.9 Two trolleys pushed close together with compressed spring
8.1
1. Name the force acting in each of the following situations (Photograph 1).
(a) Bungee jumper jumping
(b) Bicycle moving on rough surface
(c) Hot air balloon floating in the air
Photograph 1 2. Photograph 2 shows a man pushing a car. Show the direction of the pushing force and point of application of force on the photograph.
Photograph 2 174
Chapter 8 : Force and Motion
3. Photograph 3 shows a football being kicked by a player. (a) Name the forces involved in this situation. (b) Show the direction of the forces on the photograph.
Photograph 3
8.2
Effects of Force
F
orce cannot be seen but its effects can be felt. When a force acts on an object, the force can change the shape, size and motion of the object. Let us carry out Activity 8.3 to study the effects of force on an object.
A ctivity 8.3 Aim: To study the effects of force. Materials: Toy car and plasticine Apparatus: Table Instruction 1. Clear the table of your group. 2. (a) Place a toy car at one end of the table as shown in Figure 8.10. (b) Push the toy car using a force of small magnitude. Observe what happens to the stationary toy car. (c) Increase the pushing force and observe the change in the speed of the toy car. (d) Push the toy car again and ask another student to block the movement of the toy car using his hands. Observe what happens to the movement of the toy car. (e) Push the toy car again. Ask another student to push the toy car from the side. Observe what happens to the movement of the toy car. 3. Hold a piece of plasticine. Squeeze the plasticine and observe the shape and size of the plasticine. 4. Record all the observations obtained. 5. Make a conclusion about the effects of force observed.
8.2.1
Toy car Table
Figure 8.10
175
Effects of force
Situation 1 (Table tennis ball)
Moving a stationary object • When a stationary object is pushed, the object moves
Stopping a moving object • When force is applied in the opposite direction, the object will stop moving
Changing the speed of an object that is in motion
Changing the direction of motion of an object
Changing the shape and size of an object
• Force from the opposite direction slows down an object
• Force from the same direction speeds up an object
• Force from the side changes the direction of motion of an object
• Force can change the shape and size of an object
Figure 8.11 Effects of force
176
Situation 2 (Football)
Chapter 8 : Force and Motion
Buoyant Force An object will float if the buoyant force acting on it is enough to support its weight, that is buoyant force equals to the weight of the object. For example, the rubber duck below has a weight of 10 N. The reaction force, which is the buoyant force, acts with the same magnitude (10 N) but in the opposite direction (Photograph 8.6 (a)). (a)
(b)
Buoyant force = 10 N
Weight = 10 N
Buoyant force =5N
Weight = 10 N
Photograph 8.6 Condition of rubber duck and stone in water
Conversely, an object will submerge if the buoyant force acting on it is not enough to support its weight, that is buoyant force is less than the weight of the object (Photograph 8.6 (b)). Buoyant force = Actual weight – apparent weight
Science Actual weight: Weight of an object in the air. Apparent weight: Weight of an object immersed in fluid.
Let us carry out Activity 8.4 to determine the buoyant force of an object in water.
A ctivity 8.4 Aim: To determine buoyant force. Materials: Glass bottle lid, rubber stopper, squash ball, plasticine and string Apparatus: 250 ml beaker and spring balance Instruction 1. Hang a glass bottle lid at the end of a spring balance as shown in Photograph 8.7 (a). 2. Record the actual weight of the glass bottle lid, W1. 3. Fill 250 ml of water into a beaker. 4. Put the bottle lid into the water as in Photograph 8.7 (b). 5. Record the apparent weight of the bottle lid, W2. 6. Calculate the buoyant force, F. 7. Repeat steps 1 to 6 using a rubber stopper, squash ball and plasticine.
8.2.2
177
8. Put the bottle lid, rubber stopper, squash ball and plasticine into the water. Observe whether they submerge or float. 9. Record your observation in the table below.
Spring balance
Spring balance
String
Beaker
Glass bottle lid
Glass bottle lid (a)
(b) Photograph 8.7
Glass bottle lid
Rubber stopper
Squash ball
Plasticine
Actual weight, W1 (N) Apparent weight, W2 (N) Buoyant force, F (N) Submerge / float Question 1. What is the relationship between the buoyant force of an object and the condition of the object?
Density and Buoyant Effect Different materials have different densities. The position of an object in a fluid depends on the density of the object, whether it is more or less than the density of the fluid.
Will objects that are more dense than water submerge in water, while objects that are less dense than water float on water?
178
I’m not too sure. Let us carry out an experiment.
Chapter 8 : Force and Motion
Experiment 8.1
STEM
Aim: To study the effect of density on the position of an object in water. Problem statement: Will an object that is more dense than water submerge or float in water? Hypothesis: An object that is more dense than water will submerge, while an object that is less dense than water will float. Variables: (a) Constant variable: Volume of blocks (b) Manipulated variable: Density of blocks (c) Responding variable: Position of blocks in water Copper
Materials: Copper block, aluminium block, cork block and wooden block of the same size
Aluminium
Apparatus: Weighing scale, glass basin and metre rule Cork Wood Procedure: 1. Weigh the mass of each block. Figure 8.12 Four blocks with the same size 2. Calculate the volume of each block. 3. Calculate the density of each block using the following formula:
Density (g/cm3) =
Mass (g) Volume (cm3)
4. Record the mass, volume and density in the table below. Copper
Aluminium
Cork
Wood
Mass (g) Volume (cm3) Density (g/cm3) 5. Put the four blocks into a glass basin filled with water. Observe the block that floats or submerges in water. Conclusion: Is the hypothesis accepted? Give your reasons. Questions 1. Water has a density of 1.0 g cm–3. Which block is more dense than water? 2. State whether the block that is more dense than water floats or submerges in water.
F>W
W
F
Upthrust force, F
When an object that is less dense than a liquid is pushed into the liquid, the buoyant force (upthrust force, F) is more than weight (W). It pushes the object up to the surface of the liquid. The object will float (Figure 8.13).
Figure 8.13 Object floats 179
Conversely, when an object is more dense than the liquid, the buoyant force (upthrust force, F) is less than the weight of the object (W). It causes the object to submerge to the bottom of the liquid (Figure 8.14).
F