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Standard VIII Biology




All organs are made up of cells. But how different are the eyes, nose and tongue !

Did you notice Malu’s doubt? What is your opinion? .......................................................................

Are the same type of cells seen in all parts of the body? Analyse the illustration and description given below and write down the inferences in your science diary. 4


Diversity among cells Each part of the human body is made up of millions of different kinds of cells. There are about 200 different kinds of cells like nerve cells, muscle cells, blood cells, bone cells etc., in the human body.

What a wonder our body is! How do millions of such cells function effectively without getting messed up?

Yes, the human body is indeed a wonder. The well-being of the human body depends on the systematic and regulated action of the cells. Similar cells function together in groups, not separately. Such clusters of cells are called tissues.

Tissues Tissue is a group of cells that have similar structure and that function together as a unit. There are different kinds of tissues in multicellular organisms like plants and animals. The coordinated action of these tissues helps in performing different physiological functions effectively. 6

Have you observed the muscle cell and nerve cell in Illustration. Though both are cells, they differ so much in appearance. What may be the reason for the differences? How do these differences influence the physiological functions? Conduct a discussion on the description given below on the basis of the indicators.

From a single cell! Our body is developed from a single cell called zygote. The zygote undergoes continuous divisions and forms the foetus consisting cells of different shape, size and content. Foetal cells gradually attain change in structure and function. This process is known as cell differentiation.


Indicators  Formation of foetus.  Significance of cell differentiation. Write down the consolidation of the discussion in the science diary.

What are these stem cells? Are they the cells within seeds

Have you noticed Maya's doubt? What is the reason for the immense popularity gained by stem cells? Have a discussion on the description given below on the basis of the indicators. Stem cells are cells with the potential to develop into many different types of cells in the body. They serve as a repair system for the body. There are two main types of stem cells: embryonic stem cells and adult stem cells. Stem cells are specialized cells that can transform into any kind of cells. Stem cells undergo constant differentiation and get transformed into other kinds of cells. Stem cells can either get transformed into other cells through division or exist as such. When the cells in the tissues get destroyed, new cells develop from the stem cells. are found in the bone marrow, skin, digestive tract etc. 8

It is expected that the research of stem cells can bring about miraculous changes in the treatment of Blood cancer, Diabetes, Parkinson disease etc., and also in the manufacture of artificial organs.

Indicators  What are the peculiarities of stem cells when compared to other cells?  How is the destruction of cells in tissues compensated?  Why is stem cell research gaining importance? Record the consolidation of your discussion in the science dairy. Now let us read about the different types of animal tissues.


Animal Tissues Epithelial tissue  covers and protects the body.  lines the inner wall of the digestive tract.  performs functions such as protection, Absorption and production of secretions.

Nervous Tissue  controls and coordinates physiological functions.  enables to respond identifying the changes inside and outside the body.

Muscular Tissues  consists of cells that can contract and regain the original state. Enables the movement of the body.

Connective Tissue Either connects different tissues or acts as a support to them. Bone, cartilage, fibrous tissue, blood etc., are various connective tissues. Bone and cartilage provide support. Fibrous tissue connects other tissues. Blood carries out the conduction of materials and makes the body resistant to diseases


Observe the slides of animal tissues through a microscope with the help of your teacher. Prepare an illustration showing different types of tissues and their functions.

Connective Tissues As the name suggests, connective tissues bind other tissues together. Tendons that connect muscles to the bones, ligaments that connect bones together and fibrous tissues that hold the eyes and kidneys in the proper place are examples for connective tissues. Bone and cartilage, that are connective tissues help in movement and provide shape, support and strength to the body. Besides, they cover and protect internal organs. Blood, the fluid tissue, also belongs to the group of connective tissues. Blood carries out various functions like transporting respiratory gases and nutrients, providing immunity etc.

How fast does this tree grow! Why can't I grow like it

You too may have had such doubt. Is growth in plants and animals alike? Discuss…


Growth in plants is mainly centered at the tip of stems and roots. But, in animals, growth is not confined to any specific area. Why does growth in plants occur at specific areas? Find the answer by analysing the following description.

Meristematic Tissue A region of plant tissue, found chiefly at the growing tip of roots and shoots. A meristematic cell consists of a group of cells which remains in continuous state of division or they retain their power of division.

Observe the table showing the difference between meristematic and mature(permanent) tissue.

Different types of plant tissues are formed from meristematic cells. Parenchyma, collenchyma, sclerenchyma, xylem, phloem etc., are different types of plant tissues. Let's observe these tissues through a microscope. Observe the structure of a plant stem and prepare a note based on your observations.


Analyse the information given below and try to understand more about plant tissues

Plant Tissues Parenchyma $ composed of cells with the simplest structure. $ seen in the soft parts of the plant. $ helps in photosynthesis and the storage of food.

Sclerenchyma $ composed of cells that are uniformly thick all over the cell wall. $ provides strength and support to plant parts.

Collenchyma $ composed of cells that are thick only at the corners of the cell wall. $ provides flexibility and support to plant parts.


Vascular Tissues The water and minerals absorbed by roots need to be transported to leaves and the food prepared in leaves need to be transported to different parts. The specialized tissues formed from peculiar cells to do this are called vascular tissues. They are called complex tissues because they are formed from different kinds of cells. The two types of complex tissues found in plants are xylem and phloem.

Xylem $ tubes formed from elongated cells. $ transports water and minerals absorbed by the roots to the leaves. $ has thick cell walls and therefore provide support and strength to the plant. Phloem $ composed of tubular inter-connected cells. $ transports food synthesized in the leaves to various parts of the plant body. Now you have understood the different types of plant tissues and their characteristics.


Complete the following worksheet based on the hints given below. A. transports food prepared in the leaves to various parts of the plant. B. transports water and minerals absorbed by the roots to the leaves. C. seen in the tender parts of the plant. D. only the corners of the cell walls are thick. E. cells that are uniformly thick all over the cell wall are seen.

Cells combine to form tissues. What if tissues combine...?

Write your response to this. Do tissues work together just as the cells do? Tissues combine to form organs. What would happen when organs combine? Discuss Physiological functions are smoothly carried out by the combined action of many organs. Digestion is the process of the combined action of organs of the digestive system such as stomach, liver and intestine. Whether the functioning of the digestive system alone is sufficient to transport the nutrients produced by digestion, to different parts of the body? Discuss. 15

Complete the following table by finding out the systems to which the organs listed in the table belong to: Organ Heart, Blood vessels Nose, trachea, lungs Kidney, ureter, urinary bladder Brain, Nerves

Organ System

No organ system can function independently. A given physiological activity can be completed only by the combined action of different organ systems. You have understood that cells combine to form tissues, tissues combine to form organs and organs combine to form organ systems. Discuss what happens when organ systems combine together. Aren't you now convinced that an organism is a combination of different organ systems? An organism can survive only when these organ systems work in a coordinated way. As organ systems become complex, the structure of the body also becomes complex. The structure of higher order animals including human beings is complex, as it is formed by a combination of various organ systems. Do all organisms have an organ system? However unicellular organisms also exist on the earth? Discuss.


Cell is the basic unit of life. Parts of the cell are formed of various substances. Observe the illustration which shows the levels of organisation Prepare a note and record it in your science diary.

A complex living body is formed by the continuous division and differentiation of cells. In organisms that belong to higher levels of organization, different types of tissues act complementarily to perform several complex physiological activities. Efficiency of the organisms increases with the variety of its tissues. Hope you have understood the importance of functioning together. Isn't it relevant in our social life too? 17

Significant learning outcomes The learner can  identify and explain the formation of tissues from cells.  identify and explain the characteristics and functions of animal tissues.  list the characteristic features of meristematic cells.  identify and explain the formation of different types of cells from the zygote.  identify the structure of various plant tissues and list their functions.  identify and illustrate different levels of organization in organisms.

Let us assess 1. Given below in the illustration are various tissues related to the structure of hand.

Observe the illustration and write the alphabet suitable to each statement.  provides support, protection and shape :………  covers the body parts: ……….. 18

 transports substances : ………  helps to respond by recognizing changes: ………… 2. Which among the following statements is not related to tissues? a. different types of cells are seen. b. similar kinds of cells are seen. c. performs specific function. d. formed from different cells. 3. Which indicator helps to identify collenchyma when it is observed through a microscope. a. thin cell wall. b. uniformly thick cell wall. c. no nucleus in the cell. d. only the corners of the cells are thick.

Extended activities 1. Arrange an exhibition showing pictures and descriptions of different types of cells. 2. Prepare a magazine specifying the importance, relevance and scope of stem cells.