NCERT Class 7 Science Chapter 10 Respiration in Organisms

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NCERT Class 7 Science Chapter 10 Respiration in Organisms

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Respiration in Organisms

Chapter: 10


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

Ans: During the race, the athlete has to run very fast. The demand for energy at that time increases, which increase the demand for more supply of oxygen. So, athlete has to breathe faster and deep to inhale more oxygen. 

Q. 2. List the similarities and differen- ces between aerobic and anaerobic respiration.

Ans: Differences between aerobic and anaerobic respiration:

Aerobic RespirationAnaerobic Respiration
1. It occurs in the presence of oxygen.1. It occurs in the absence of oxygen.
2. Food molecules are broken down into water and carbon dioxide.2. Food molecules are broken down into ethyl alcohol and carbon dioxide. 
3. Large amount of energy is released.3. Small amount of energy is released.

Similarities: Both aerobic and anaerobic respiration produce energy and give out carbon dioxide.

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

Ans: We sneeze to get rid of the unwanted particles like dust etc., from our body. It allows only clean and dust free air to enter our body. 

Q.4. Take three test-tubes. Fill 3/4th of each tube with water. Label them A, B and C. Keep a snail in a 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: There will be highest concentration of CO2 in tube A.

Q. 5. 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: (d) (ii) Move downwards. 

Q. 6. Match the items in Column I with those in Column II:

Column – IColumn – II
(a) Yeast(i) Earthworm
(b) Diaphragm(ii) Gills
(c) Skin(iii) Alcohol
(d) Leaves(iv) Chest cavity
(e) Fish(v) Stomata
(f) Frog(vi) Lungs and skin (vii) Trachea


Column – IColumn – II
(a) Yeast(iii) Alcohol
(b) Diaphragm(iv) Chest cavity
(c) Skin(i) Earthworm
(d) Leaves(v) Stomata
(e) Fish(ii) Gills
(f) Frog(vi) Lungs and skin

Q. 7. 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)

Ans: False.

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

Ans: False.

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

Ans: True.

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

Ans: False.

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

Ans: True.

Q. 8. Given below is a square of letters in which are hidden different words related to respiration in organisms. These words may be present in any direction-upwards, downwards, or along the diagonals. Find the words for your respiratory system. Clues about those words are given below the square.

(i) The air tubes of insects. 

Ans: Trachea.

(ii) Skeletal structures surrounding chest cavity.

Ans: Ribs.

(iii) Muscular floor of chest cavity. 

Ans: Diaphragm.

(iv) Tiny pores on the surface of leaf.

Ans: Stomata.

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

Ans: Spiracles.

(vi) The respiratory organs of human beings.

Ans: Lungs.

(vii) The openings through which we inhale. 

Ans: Nost- rils.

(viii) An anaerobic organism.

Ans: Yeast.

(ix) An organism with tracheal system.

Ans: Ant.

Q. 9. 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.


Very Short Answer type Questions 

Q. 1. Which process of respiration releases more energy?

Ans: Aerobic respiration.

Q. 2. What is the function of hair and mucus that line the passage of nostrils?

Ans: It helps in filtering air when the air is taken in to the body through the nostrils.

Q. 3. What are stomata?

Ans: Stomata are the tiny pores present on the surface of leaves. 

Q. 4. Name the process by which energy is released from the digested food.

Ans: Respiration.

Q. 5. (a) Name the skeletal structure surrounding the chest cavity. 

Ans: Rib cage.

(b) Name the muscular floor of the chest cavity.

Ans: Diaphragm.

Q. 6. In the lungs.

(a) What substance is taken into the body? 

Ans: Oxygen.

(b) What substance is removed from the body?

Ans: Carbon dioxide.

Q. 7. Give two functions of stomata.

Ans: (i) Gaseous exchange in respiration. 

(ii) Loss of water in the form of transpiration.

Q. 8. What are the end products of anaerobic respiration in yeasts? 

Ans: Ethyl alcohol and carbon dioxide.

Q. 9. What are the end products of aerobic respiration?

Ans: Carbon dioxide and water.

Q. 10. Which gas is released during exhalation?

Ans: Mainly carbon dioxide.

Q. 11. What type of respiration takes place in human muscles during vigorous physical exercise?

Ans: Anaerobic respiration.

Q. 12. Name the substance build up in the muscles during vigorous physical exercise may cause cramps.

Ans: Lactic acid.

Q. 13. Name the process by which plant parts like roots, stems and leaves get oxygen required for respiration.

Ans: Diffusion. 

Q. 14. Name the organ of breathing in fish.

Ans: Gills.

Q. 15. Write the respiratory organs in frog and earthworm.

Ans: Frog: A pair of lungs and skin

Earthworm: Moist skin.

Short Answer type Questions 

Q. 1. From where do the following take in oxygen?

(i) Prawn. 

Ans: Prawn: from water through gills

(ii) Rat.

Ans: Rat: from air through lungs.

Q. 2. What happens to the rate of breathing during vigorous exercise and why?

Ans: The rate of breathing increases at the time of physical activities because the demand of oxygen increases. The rate of breathing increases upto 20 to 25 times per minute during vigorous exercise.

Q. 3. How do roots respire?

Ans: Roots take oxygen present in between soil particles by the process of diffusion with the help of root hair, similarly carbon dioxide is released out.

The older parts perform respiration by means of lenticles as root hair are absent in these areas.

Q. 4. Give two points of difference between respiration in plants and respiration in animals.


Respiration in PlantsRespiration in Animals
1. All parts of a plant like the root, stem, leaf perform respi- ration individually.1. Animals have specific organs for respiration.
2. There is a little transport of gases from one part of plant to another.2.There occurs transport of gases from one part of animal to another.

Q. 5. Why is rate of breathing in aquatic organisms much faster than in terrestrial organisms?

Ans: The amount of dissolved oxygen in water is fairly low compared to the amount of oxygen in the air. Therefore, rate of breathing in aquatic organisms is much faster than in terrestrial organisms.

Q. 6. What changes occur in the chest cavity and lungs during inhalation?

Ans: The volume of the chest cavity and the lungs expand. As a result pressure inside the lungs decreases and fresh air rushes into the lungs. During inhalation the chest expands.

Q. 7. What is the function of large inter cellular spaces in plants?

Ans: The large intercellular spaces ensure that all cells are in contact with air. Both CO₂ and O, are exchanged by diffusion in the inter- cellular spaces. These gases can either go into cells, or away from them and out into the air.

Q. 8. How does fish obtain oxygen for breathing and respiration?

Ans: The fish has special organs of breathing called gills. The fish breathes by taking in water through its mouth and sending it over the gills. When water passes over the gills, the gills extract dissolved oxygen from this water. This oxygen is absorbed by the blood and carried to all the parts of the fish.

Q. 9. Why do fishes die when taken out of water?

Ans: Fishes respire with the help of gills. Gills are richly supplied with blood capillaries and can readily absorb oxygen dissolved in water. Since fishes cannot absorb gaseous oxygen they die soon after they are taken out of water.

Q. 10. What is the importance of breathing?

Ans: All the organisms need energy for their various functions. This energy released from the breakdown of food (glucose) with the help of oxygen. The breathing ensure the continuous supply of oxygen to different body cells.

Short Answer type Questions 

Q. 1. Differentiate between breathing and respiration.

Ans: Breathing and respiration have following differences:

1. It is a physical process.1. It is a biochemical process.
2. Takes place outside the cells.2. Takes place inside- the cells.
3. No energy is released.3. Energy is released.

Q. 2. Why is diffusion insufficient to meet the oxygen requirements of large multicellular organisms like humans?

Ans: Diffusion is insufficient to meet the oxygen requirements of large multicellular organisms like humans because the volume of human body is so big that oxygen cannot diffuse into all the cells of the human body quickly. This is because oxygen will have to travel large distances inside the human body to reach and every cell of the body. Diffusion being a very slow process will take a lot of time to make oxygen available to all the body cells. So, when the size of multicellular organism is large, then respiratory pigments (such as haemoglobin) present in blood take up the oxygen from the air in the lungs and carry it quickly to all the body cells.

Q. 3. What are the common features of respiratory organs in animals? 

Ans: The common features of respiratory organs in animals are:

(i) A large surface area to get enough oxygen. 

(ii) Thin walls for easy diffusion and exchange of respiratory gasses. 

(iii) In the tracheal system, air reaches cells directly whereas in other respiratory organs have rich blood supply for transportation of gasses.

Q. 4. How do exchange of gasses take place in aquatic animals?

Ans: Most of the aquatic animals like prawns, fish, tadpoles, use gills as the respiratory organs. Respiration through gills is known as bronchial respiration. The blood flowing in the capillaries of gills absorb oxygen and gives carbon dioxide to the water passing over them by diffusion through thin epithelium.

Long Answer Type Questions

Q. 1. What is aerobic respiration? Explain its mechanism. What are its end products?

Ans: The process of respiration taking place in the presence of air (oxygen) is called aerobic respiration.

Mechanism: During aerobic respiration, glucose molecule (a six carbon molecules) is broken down into pyruvate (a three carbon molecules) in the cytoplasm. Further break down of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three carbon pyruvate molecules to give three molecules of CO,. The other product is water. The break down of a glucose molecule produces 36 ATP.

Q. 2. Three test-tubes are taken and labelled A, B and C. Each test tube is half filled with water:

The three test tubes are then placed in sunlight. Which test tube would have the highest concentration of carbon dioxide ? Why?

(a) In test tube A, a snail is kept

Ans: Test tube A contains a snail in water. The snail will use up oxygen for respiration and produces carbon dioxide.

(b) In test tube B, a water plant is kept, and 

Ans: Test tube B contains a water plant in water. The water plant will use some of this oxygen for respiration and produce carbon dioxide. This carbon dioxide will then be used by the plant in photosynthesis.

(c) In test tube C, a snail and a water plant, both are kept.

Ans: Test tube C contains both, a snail and a water plant. The carbon dioxide produced by the respiration in snail will be all used up by the water plant in photosynthesis.

From this, we conclude that the test tube A containing only snail will have the highest concentration of carbon dioxide because there is no plant to use up the carbon dioxide produced during the respiration in snail.

Q. 3. Which contains more carbon dioxide: Exhaled air or inhaled air? Why?

Ans: More carbon dioxide is present in exhaled air. Inhaled air contains small amount of carbon dioxide which is normally present in the atmosphere. Now, when we inhale air, then the oxygen present in it oxidizes the food present in body cells to produce carbon dioxide, water and energy. This carbon dioxide produced in the body cells during respiration increases the amount of carbon dioxide in exhaled air.


Q.1. In an experiment to demonstrate the mechanism of breathing by using a bell jar, two balloons in the bell jar and a rubber sheet tied to the open end of hell jar: 

(a) What does the space in the bell jar represent?

Ans: Chest cavity.

(b) What do the balloons in the bell jar represent?

Ans: Lungs.

(c) What does the rubber sheet tied over the open end of bell jar represent?

Ans: Diaphragm.

Q. 2. After a vigorous exercise, you may experience cramps in your leg muscles. Why does this happen? 

Ans: This happens due to build up of lactic acid in our muscles. During heavy exercise, there is lack of oxygen on our muscle cells and therefore another path way for the breakdown of pyruvate to lactic acid takes place.

Q. 3. Consider the following animals: 

Fish, Grasshopper, Cockroach, Earthworm Frog, Cow, Goat, Man, Lizard, Snake.

Which of these animals:

(a) breathe only through skin?

Ans: Earthworm.

(b) breathe through skin as well as lungs?

Ans: Frog.

(c) breathe only through lungs? 

Ans: Cow, Goat, Man, Lizard, Snake.

(d) breathe through spiracles and tracheas?

Ans: Grasshopper. Cockroach.

(e) breathe through gills? 

Ans: Fish.


Q. 1. Draw a diagram of a part of fish and indicates the position of gills in a bony fish.


Q. 2. (f) Draw a diagram in which roots absorb air from the soil is indicated.

(ii) Label the following: 

(a) Root hair

(b) Air space

(c) Soil particles.


Q. 3. Draw diagram of open and closed stomata.



1. Fill in the following blanks with suitable words:

(i) The process of respiration is the reverse of ________.

Ans: Photosynthesis.

(ii) Food can also be broken down without using _______.

Ans: Oxygen.

(iii) Anaerobic respiration in muscles occurs if there is no _______ available. 

Ans: Oxygen.

(iv) Anaerobic respiration by yeast converts glucose into _______ which is used in making wine and beer. 

Ans: Alcohol.

(v) If a person is doing exercise, his breathing rate ________.

Ans: Increases.

(vi) During inhalation ribs move and diaphragm ________.

Ans: Up and upwards, move down.

(vii) Cockroach respires through ________ and _________.

Ans: Tracheas, spiracles.

(viii) The air trapped in the soil diffuses with rough _________.

Ans: Epiblema (cells in the root).

(ix) Frogs respire through ________ when in ________.

Ans: Skin, water.

(x) The chest cavity __________ during exhalation. 

Ans: Contracts/decreases.

2. State whether the following statements are true or false :

(i) Respiration is a type of combustion at ordinary temperature.

Ans: True.

(ii) Oxygen is released during the process of respiration.

Ans: False.

(iii) Energy can be released in the cells with- out oxygen. 

Ans: True.

(iv) During heavy exercise, the breathing rate of a person slows down.

Ans: False.

(v) The size of chest cavity increases during inhalation.

Ans: True.

(vi) Tracheas have large surface area for gas exchange. 

Ans: True.

(vii) Oxygen and carbon dioxide diffuse through the walls of alveoli.

Ans: True.

(viii) Frogs breathe through their skin as well as their lungs.

Ans: True.

(ix) The size of the chest cavity increases during inhalation.

Ans: True.

(x) Plants carry out photosynthesis only during the day and respiration only at night.

Ans: False.

3. Write one word for the following: 

(i) The process of inhaling fresh air and exhaling the used air.

Ans: Breathing.

(ii) Respiration in the presence of oxygen.

Ans: Aerobic respiration.

(iii) Number of times a person breathes in one minute. 

Ans: Breathing rate.

(iv) Small air sacs at one end of bronchioles.

Ans: Alveoli.

(v) A process in plants that occurs in mitochondria. 

Ans: Respiration.

(vi) A large flat muscular sheet which forms the floor of the chest cavity.

Ans: Diaphragm.

(vii) Giving out of air rich in carbon dioxide during breathing. 

Ans: Exhalation.

(viii) Taking in of air rich in oxygen during breathing.

Ans: Inhalation.

(ix) Organs of respiration in fishes. 

Ans: Gills.

(x) Organs of gaseous exchange in higher animals.

Ans: Lungs.

4. Multiple Choice Questions:

(i) Which of the following is not a part of the human respiratory system?

(a) lungs 

(b) Esophagus

(c) trachea

(b) esophagus

Ans: (d) Diaphragm

(ii) One of the following is not produced during the anaerobic respiration in yeast. 

This one is: 

(a) carbon dioxide

(b) energy

(c) lactic acid

(d) alcohol

Ans: Lactic acid

(iii) Which of the following is not a product of aerobic respiration?

(a) carbon dioxide

(b) alcohol

(c) energy

(d) water

Ans: (b) Alcohol.

(iv) Yeast converts glucose into: 

(a) starch

(b) alcohol

(c) lactic acid 

(d) yogurt

Ans: (b) Alcohol.

(v) During respiration in humans, the exchange of gasses takes place in:

(a) bronchi

(b) alveoli

(c) bronchioles

(d) trachea

Ans: (b) Alveoli.

(vi) Which of the following does not have lungs for breathing? 

(a) lizard

(b) frog

(c) fish

(d) fox

Ans: (c) Fish.

(vii) Which of the following is most likely to have a much higher breathing rate?

(a) man

(b) dog

(c) sparrow 

(d) fish

Ans: (d) Fish

(viii) The process by which food (glucose) is broken down to release energy is called:

(a) digestion

(b) photosynthesis

(c) circulation

(d) respiration

Ans: (d) Respiration.

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