10. Respiration in Organisms | Class 7

Q1: Why does an athlete breathe faster and deeper than usual after finishing the race?

Answer: When an athlete runs in a race, his body demands more oxygen than in normal case. To meet this demand of more oxygen he increases his rate of breathing and thus the oxygen is supplied to the entire body. Hence an athlete needs to breathe faster and deeper than usual; after finishing the race.

Q2: List the similarities and differences between aerobic and anaerobic respiration.

Ans: The similarities and differences between aerobic and anaerobic respiration are as follows:

Similarities: Food is oxidized in both cases and energy is released.


(a) Carbon dioxide and water are the end products of aerobic respiration, while alcohol or lactic acid is the end product of anaerobic respiration.

(b) Aerobic respiration is more efficient than anaerobic respiration.

Q3: Why do we often sneeze when we inhale a lot of dust-laden air?

Ans: When dust particles enter our nostril, a message is triggered to the brain. Therefore the brain instructs the nasal chamber to initiate sneezing. Sneezing is a defence mechanism of the body to prevent the unwanted dust particles from entering the nostrils.

Q4: 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?

Ans: Test tube A will have the highest concentration of carbon dioxide. The carbon dioxide comes because of respiration by the snail. In test tubes B and C; a part of the carbon dioxide is utilized by the plant for photosynthesis and hence there is less concentration of carbon dioxide.

Q5: Tick the correct answer:

(a) In cockroaches, air enters the body through

(i) lungs
(ii) gills
(iii) spiracles
(iv) skin

Ans: (iii) Spiracles

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

(i) carbon dioxide
(ii) lactic acid
(iii) alcohol
(iv) water

Ans: (ii) Lactic acid

(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

Ans: (ii) 15 – 18

(d) During exhalation, the ribs

(i) move outwards
(ii) move downwards
(iii) move upwards
(iv) do not move at all

Ans: (ii) Move downwards

Q6: Match the items in Column I with those in Column II:

Column I                                  Column II
(1) Yeast                                    (a) Earthworm
(2) Diaphragm                         (b) Gills
(3) Skin                                     (c) Alcohol
(4) Leaves                                 (d) Chest cavity
(5) Fish                                      (e) Stomata
(6) Frog                                     (f) Lungs and skin

Ans: 1 → b,  2 → d,  3 → a,   4 → e,   5 → b,  6 → f

Q7: Mark ‘T’ if the statement is true and ‘F’ if it is false:

a.) During heavy exercise the breathing rate of a person slows down.
b.) Plants carry out photosynthesis only during the day and respiration only at night.
c.) Frogs breathe through their skins as well as their lungs.
d.) The fishes have lungs for respiration.
e.) The size of the chest cavity increases during inhalation.

Ans: (a) F, (b) F, (c) T, (d) F, (e) T

Q8: The mountaineers carry oxygen with them because:

a) At an altitude of more than 5 km there is no air.
b) The amount of air available to a person is less than that available on the ground.
c) The temperature of air is higher than that on the ground.
d) The pressure of air is higher than that on the ground.

Ans: (b) The amount of air available to a person is less than that available on the ground



1. What do you mean by Cellular Respiration ?

Ans. In the cells of all living organisms, 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.

2. Define Aerobic Respiration

Ans. When breakdown of glucose occurs with the use of oxygen it is called aerobic respiration.

3. Define Anaerobic Respiration

Ans. Food can also be broken down, without using oxygen. This is called anaerobic respiration.

4. What are aneorobes, give an example ?

Ans. 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.

5. Describe Aneaerobic Respiration in Humans with an example ?

Ans. 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, cycling, walking for many 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 fulfill the demand of energy:

Glucose (in absence of oxygen)     –  —–>      lactic acid + energy

The muscle cramps occur when muscle cells respire anaerobically. The partial breakdown of glucose produces lactic acid. The accumulation of lactic acid causes muscle cramps.

6. Why do we get relies from muscle cramps after a hot water bath or a massage ?

Ans. The cramps occur when muscle cells respire anaerobically. The partial breakdown of glucose produces lactic acid. The accumulation of lactic acid causes muscle cramps. We get relief from cramps after a hot water bath or a massage because the hot water bath or massage improves circulation of blood. As a result, the supply of oxygen to the muscle cells increases. The increase in the supply of oxygen results in the complete breakdown of lactic acid into carbon dioxide and water.

7. What do you mean by breathing and also a breath ?

Ans. Breathing means taking in air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs. The taking in of air rich in oxygen into the body is called inhalation and giving out of air rich in carbon dioxide is known as exhalation. It is a continuous process which goes on all the time and throughout the life of an organism. The number of times a person breathes in a minute is termed as the breathing rate. During breathing inhalation and exhalation take place alternately. A breath means one inhalation plus one exhalation.

8. Describe the mechanism of breathing ?

Ans. Normally we take in air through our nostrils. When we inhale air, it passes through our nostrils into the nasal cavity. From the nasal cavity, the air reaches our lungs through the windpipe. Lungs are present in the chest cavity. This cavity is surrounded by ribs on the sides. A large, muscular sheet called diaphragm forms the floor of the chest cavity (Fig. 10.4). Breathing involves the movement of the diaphragm and the rib cage. During inhalation, ribs move up and outwards and diaphragm moves down. This movement increases space in our chest cavity and air rushes into the lungs. The lungs get filled with air. During exhalation, ribs move down and inwards, while diaphragm moves up to its former position. This reduces the size of the chest cavity and air is pushed out of the lungs (Fig. 10.5).

9. How does sneezing expel the foreign/ dust particles from inhaled air ?

Ans. The air around us has various types of unwanted particles, such as smoke, dust, pollens, etc. When we inhale, the particles get trapped in the hair present in our nasal cavity. However, sometimes these particles may get past the hair in the nasal cavity. Then they irritate the lining of the cavity, as a result of which we sneeze. Sneezing expels these foreign particles from the inhaled air and a dust-free, clean air enters our body.

10. How does breathing take place in insect like a cockroach ?

Ans. A cockroach has small openings on the sides of its body. Other insects also have similar openings. These openings are called spiracles (Fig. 10.9). Insects have a network of air tubes called tracheae for gas exchange. Oxygen rich air rushes through spiracles into the tracheal tubes, diffuses into the body tissue, and reaches every cell of the body. Similarly, carbon dioxide from the cells goes into the tracheal tubes and moves out through spiracles. These air tubes or tracheae are found only in insects and not in any other group of animals.

11. How does an earthworm breath?
Ans. Earthworms breathe through their skins. The skin of an earthworm feels moist and slimy on touching. Gases can easily pass through them. Though frogs have a pair of lungs like human beings, they can also breathe through their skin, which is moist and slippery.

12. How is breathing carried out in organisms that live in water particularly a fish ?

Ans. There are many organisms which live in water. In case of fish the gills help them to use oxygen dissolved in water. Gills are projections of the skin. Gills are well supplied
with blood vessels (Fig. 10.10) for exchange of gases.

13. Do plants respire, explain how ?

Ans. Like other living organisms, plants also respire for their survival. They also take in oxygen from the air and give out carbon dioxide. In the cells oxygen is used to break down glucose into carbon dioxide and water as in other organisms. In plants each part can independently take in oxygen from the air and give out carbon dioxide through tiny pores called stomata for exchange of oxygen and carbon dioxide. Like all other living cells of the plants, the root cells also need oxygen to generate energy. Roots take up air from the air spaces present between the soil particles (Fig. 10.11).


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