Course Content
Class 7th Science
Class 7th Math
Online Class For 7th Standard Students (CBSE)
About Lesson

Question 1.
Why does an athlete breathe faster and deeper than usual after finishing the race?
An athlete requires more energy during and after the race. Since demand for energy is high, so oxidation of food must be speeded up. This requires more oxygen to be supplied. This is why an athlete not only breathes fast but also takes deep breathes and thus inhales more oxygen.

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

  1. Energy is released
  2. Carbon dioxide is produced.


  1. Anaerobic respiration does not require oxygen while areobic respiration takes place in the presence of oxygen.
  2. Glucose is completely broken down in aerobic respiration but not in anaerobic respiration.

Question 3.
Why do we often sneeze when we inhale a lot of dust-laden air?
When we inhale dust particles, pollens, etc., the particles get trapped in the hair present in our nasal cavity. However, sometimes these particles may pass the hair in the nasal cavity, where they irritate the lining of the cavity, as a result of which we sneeze. Sneezing expels these foreign particles from the inhaled air and dust-free, clean air enters our body.

Question 4.
Take three test-tubes. Fill 1/3 rd of each with water. Label them A, B and C. Keep a snail in the 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 a snail will tape in oxygen and gives out CO2In test-tube B and C, the CO2 will be utilized by the water plant for synthesizing food, and hence there will be less concentration of CO2 in there.

Question 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 accumulation 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

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

Column I Column 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) Tracheae


Question 7.
Mark ‘T’ if the statement is True and ‘F’ if it is False:

  1. During heavy exercise, the breathing rate of a person slows down. (T/F)
  2. Plants carry out photosynthesis only during the day and respiration only at night. (T/F)
  3. Frogs breathe through their skins as well as their lungs. (T/F)
  4. The fishes have lungs for respiration.(T/F)
  5. The size of the chest cavity increases during inhalation. (T/F)


  1. F
  2. F
  3. T
  4. F
  5. T.

Question 8.
Given below is a square of letters in which different words related to respiration in organisms are hidden. 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.

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