Class 7 Science Chapter 10 | Respiration in Organisms | Textbook Solutions

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

Running a race requires a lot of energy. In order to release more energy more oxygen has to be supplied to the cells. Since the normal rate of breathing cannot supply that much oxygen, during intense activities like running, muscle cells perform anaerobic respiration to produce energy. Anaerobic respiration results in the partial breakdown of glucose and produces lactic acid and energy. Once the race is over, the athlete breathes faster so that more oxygen can be supplied to the cells and lactic acid can be broken down into carbon dioxide and water.

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


Both processes release oxygen.

Both processes occur in living cells.


Aerobic respiration takes place in the presence of oxygen. It results in the breakdown of glucose into carbon dioxide, water and energy.

Anaerobic respiration does not use oxygen. It results in the breakdown of glucose into carbon dioxide, alcohol and energy.

Aerobic respiration releases energy in higher amounts.

Anaerobic respiration releases energy in smaller amounts.

Aerobic respiration takes place in plants and animals.

Anaerobic respiration takes place in bacteria, yeast and muscle cells

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

The air contains various unwanted particles and when we breathe, these particles get trapped in the hair present in our nasal cavity. Sometimes these particles get past the nasal cavity and when they do so they irritate the cavity. This leads to sneezing. Sneezing expels unwanted particles from the inhaled air.

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4. Take three test-tubes. Fill each of them 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?

Test-tube A will have the highest concentration of CO2 because during the process of breathing, the snail will take in oxygen and release carbon dioxide. Test tubes B and C will have lower levels of carbon dioxide because the water plants will utilize it to synthesize food.

5. Tick the correct answer:

a) In cockroaches air enters the body through spiracles.

b) During heavy exercise, we get cramps in the legs due to the accumulation of lactic acid

c) Normal range of breathing rate per minute in an average adult person at rest is 15 – 18

d) During exhalation, the ribs move downwards

6. Match the items


a) Yeast – Alcohol

b) Diaphragm – Chest cavity

c) Skin – Earthworm

d) Leaves – Stomata

e) Fish – gills

f) Frog – lungs and skin

7. True or False

(i) During heavy exercise, the breathing rate of a person slows down – False

(ii) Plants carry out photosynthesis only during the day and respiration only at night – False

(iii) Frogs breathe through their skins as well as their lungs – True

(iv) The fishes have lungs for respiration – False

(v) The size of the chest cavity increases during inhalation – True

8. Solution

(i) The air tubes of insects – trachea

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(ii) Skeletal structures surrounding chest cavity – ribs

(iii) Muscular floor of chest cavity – diaphragm

(iv) Tiny pores on the surface of leaf – stomata

(v) Small openings on the sides of the body of an insect – spiracles

(vi) The respiratory organs of human beings – lungs

(vii) The openings through which we inhale – nostrils

(viii) An anaerobic organism – yeast

(ix) An organism with tracheal system – ant

9. The mountaineers carry oxygen with them because (b) The amount of air available to a person is less than that available on the ground.

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