NCERT Class VII Science Solutions: Chapter 10-Respiration in Organisms Part 3 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 11:

On an average, an adult human being at rest breathes 15 - 18 times per minute. The breathing rate, however, may differ under different conditions. Arrange the following activities given in the box in order of increasing breathing rates and give reason for your answer.

Sleeping, cycling, brisk walk, watching TV.


Sleeping > watching T. V. > brisk walk > cycling

Whenever a person does an activity, the breathing rate becomes faster. It further increases with strenuous work to provide more oxygen to the cells to get more energy.

Question 12:

On a very cold morning, Boojho and Paheli were talking with each other as they walked down to their school. They observed that the air coming out of their mouth looked like smoke. They were amused and wondered how it happened. Help them find the answer.


On a cold day, the warm and moist air exhaled by us condenses into mist when it comes in contact with the cold air of the atmosphere. This looks like white smoke.

Question 13:

Whenever we feel drowsy or sleepy, we start yawning. Does yawning help us in anyway?


During drowsiness, our breathing rate slows down. The lungs do not get enough oxygen from the air resulting in yawning. Yawning brings extra oxygen into the lungs and helps us to keep awake.

Question 14:

Insects and leaves of a plant have pores through which they exchange gases with the atmosphere. Can you write two points of differences between these pores with respect to their position, number and extension into the body?


  1. Spiracles are present on the sides of insects՚ body while stomata are present on the lower surface of leaves.
  2. Spiracles are fewer in number as compared to stomata.
  3. Spiracles lead to an extensive network of tracheal system which is absent in the leaves.

(You can add more)


Question 15:

Paheli participated in a race competition held at her school and won the race. When she carne home she had mixed feelings of joy and pain as she had cramps in her leg muscles.

After a massage she was relieved of the pain. Answer the following questions related to the situation.

  1. What can be the possible reasons for the pain in her legs?
  2. Why did she feel comfortable after a massage?


  1. The pain in her legs could be because of the accumulation of lactic acid in the muscles. During heavy exercise or running. etc. , the muscle cells respire anaerobically and produce lactic acid.
  2. The massage gave her relief because it improves the circulation of blood leading to increased supply of oxygen to the muscle cells which helps in complete breakdown of lactic acid into and water.