NCERT Class 7 Science Respiration in Organisms

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10 Respiration in Organisms

One day Boojho was eagerly waiting to meet his grandparents who were coming to the town after a year. He was in a real hurry as he wanted to receive them at the bus-stop. He ran fast and reached the bus-stop in a few minutes. He was breathing rapidly. His grandmother asked him why he was breathing so fast. Boojho told her that he came running all the way. But the question got stuck in his mind. He wondered why running makes a person breathe faster. The answer to Boojho’s question lies in understanding why we breathe. Breathing is a part of respiration. Let us learn about respiration.

10.1 WHY DO WE RESPIRE?

In Chapter 2 you learnt that all organisms are made of small microscopic units called cells. A cell is the smallest structural and functional unit of an organism. Each cell of an organism performs certain functions such as nutrition, transport, excretion and reproduction. To perform these functions, the cell needs energy. Even when we are eating, sleeping or reading we require energy. But, where does thisenergy come from? Can you say why your parents insist that you should eat regularly? The food has stored energy, which is released during respiration.

Therefore, all living organisms respire to get energy from food. During breathing, we breathe in air. You know that air contains oxygen. We breathe out air which is rich in carbon dioxide. The air we breathe in is transported to all parts of the body and ultimately to each cell. In the cells, oxygen in the air helps in the breakdown of food. The process of breakdown of food in the cell with the release of energy is called cellular respiration. Cellular respiration takes place in the cells of all organisms.

In the cell, the food (glucose) is broken down into carbon dioxide and water using oxygen. When breakdown of glucose occurs with the use of oxygen it is called aerobic respiration. Food can also be broken down, without using oxygen. This is called anaerobic respiration. Breakdown of food releases energy. With the use of oxygen Glucose carbon dioxide + water + energy

You should know that there are some organisms such as yeast that can survive in the absence of air. They are called anaerobes. They get energy through anaerobic respiration. In the absence of oxygen, glucose breaks down into alcohol and carbon dioxide, as given below: Without the use of oxygen Glucose alcohol + carbon dioxide + energy

Our muscle cells can also respire anaerobically, but only for a short time, when there is a temporary deficiency of oxygen. During heavy exercise, fast running (Fig. 10.1), cycling, walking formany hours or heavy weight lifting, the demand for energy is high. But the supply of oxygen to produce the energy is limited. Then anaerobic respiration takes places in the muscle cells to fulfil the demand of energy:

Exercises

1. Why does an athlete breathe faster and deeper than usual after finishing the race?

2. List the similarities and differences between aerobic and anaerobic respiration.

3. Why do we often sneeze when we inhale a lot of dust-laden air?

4. Take three test-tubes. Fill th of each with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of CO2?

5. Tick the correct answer:

(a) In cockroaches, air enters the body through

(i) lungs                  (ii) gills

(iii) spiracles           (iv) skin

(b) During heavy exercise, we get cramps in the legs due to the accu mulation of

(i) carbon dioxide    (ii) lactic acid

(iii) alcohol             (iv) water

(c) Normal range of breathing rate per minute in an average adult person at rest is:

(i) 9–12                  (ii) 15–18

(iii) 21–24               (iv) 30–33

(d) During exhalation, the ribs

(i) move outwards    (ii) move downwards

(iii) move upwards    (iv) do not move at all

6. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) During heavy exercise the breathing rate of a person slows down. (T/F)

(ii) Plants carry out photosynthesis only during the day and respiration only at night. (T/F)

(iii) Frogs breathe through their skins as well as their lungs. (T/F)

(iv) The fishes have lungs for respiration. (T/F)

(v) The size of the chest cavity increases during inhalation. (T/F)


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