NCERT Class 7 Science Transportation in Animals

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11 Transportation in Animals

 and Plants 

You have learnt earlier that all organisms need food, water and oxygen for survival. They need to transport all these to various parts of their body. Further, animals need to transport wastes to parts from where they can be removed. Have you wondered how all this is achieved? Look at Fig. 11.1. Do you see the heart and the blood vessels? They function to transport substances and together form the circulatory system. In this chapter you shall learn about transport of substances in plants and animals.

11.1 CIRCULATORY SYSTEM 

What happens when you get a cut on your body? Blood flows out. But what is blood? Blood is the fluid which flows in blood vessels. It transports substances like digested food from the small intestine to the other parts of the body. It carries oxygen from the lungs to the cells of the body. It also transports waste for removal from the body.

How does the blood carry various substances? Blood is a liquid, which has cells of various kinds suspended in it. The fluid part of the blood is called plasma. One type of cells are the red blood cells (RBC) which contain a red pigment called haemoglobin. Haemoglobin bind with oxygen and transports it to all the parts of the body and ultimately to all the cells. It will be difficult to provide oxygen efficiently to all the cells of the body without haemoglobin. The presence of haemoglobin makes blood appear red.

The blood also has white blood cells (WBC) which fight against germs that may enter our body. Boojho fell down while playing a game and his knee got injured. Blood was coming out from the cut. After some time, he noticed that bleeding had stopped and a dark red clot had plugged the cut. Boojho was puzzled about this.The clot is formed because of the presence of another type of cells in the blood, called platelets. Blood vessels 

There are different types of blood vessels in the body. You know that during inhalation a fresh supply of oxygen fills the lungs. Oxygen has to be transported to the rest of the body. Also, the blood picks up the waste materials including carbon dioxide from the cells. This blood has to go back to the heart for transport to the lungs for removal of carbon dioxide as you have learnt in Chapter 10. So, two types of blood vessels are present in the arteries and veins of the body. (Fig. 11.1) Arteries carry oxygen-rich blood from the heart to all parts of the body. Since the blood flow is rapid and at a high pressure, the arteries have thick elastic walls. Let us perform an activity to study the flow of blood through arteries.

Exercises

1. Fill in the blanks.

(i) The blood from the heart is transported to all parts of the body by the .

(ii) Haemoglobin is present in cells.

(iii) Arteries and veins are joined by a network of .

(iv) The rhythmic expansion and contraction of the heart is called

(v) The main excretory product in human beings is .

(vi) Sweat contains water and .

(vii) Kidneys eliminate the waste materials in the liquid form called

(viii) Water reaches great heights in the trees because of suction pull caused by

2. Choose the correct options:

(a) In plants, water is transported through

(i) Xylem             (ii) Phloem

(iii) Stomata        (iv) Root hair

(b) Water absorption through roots can be increased by keeping the plants

(i) in the shade

(ii) in dim light

(iii) under the fan

(iv) covered with a polythene bag

3. Why is transport of materials necessary in a plant or in an animal? Explain.

4. What will happen if there are no platelets in the blood?

5. What are stomata? Give two functions of stomata.

6. Does transpiration serve any useful function in the plants? Explain.

7. What are the components of blood?

8. Why is blood needed by all the parts of a body?

9. What makes the blood look red?

10. Describe the function of the heart.

11. Why is it necessary to excrete waste products?

12. Draw a diagram of the human excretory system and label the various parts.


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