Class 7, Respiration in Organisms | NCERT (CBSE) science | Solutions of NCERT textbook exercise questions


Class VII, Science
Respiration in Organisms
NCERT Solutions of Textbook Exercise (Important Questions Only)
Q.1: Why does athlete breathe faster and deeper than usual after finishing the race?  
Solution: An athlete needs more energy during the race and after. Since demand for the energy is high the breakdown of food must be speeded up. This requires more oxygen to be supplied. This is why an athlete not only breathes fast, but also take deep breathes and thus inhale more oxygen.

Q.2: List the similarities and differences between aerobic and anaerobic respiration.
Solution: The following table shows the similarities and differences between aerobic and anaerobic respiration:

Aerobic Respiration
Anaerobic Respiration
  • It is the process of breakdown of glucose in the presence of oxygen. 
  • Glucose is completely oxidized. 
  • The end products formed are CO2, H2O and energy. 
  • Energy released is more. 
  • It takes place in all higher organisms. 
  • Reaction is:
     Glucose + Oxygen => 
      Carbon dioxide + Energy
  • It is the process of breakdown of glucose in the absence of oxygen. 
  • Glucose is incompletely oxidized. 
  • The end products formed are CO2, ethyl alcohol and energy. 
  • Energy released is less. 
  • It takes place in lower organisms like yeast and muscles of man. 
  • Reaction is: 
      Glucose => Ethyl alcohol + CO2 + Energy

Q.3: Why we often sneeze when we inhale a lot of dust-laden air?
Solution: The air around us has various types of unwanted suspended particles like- smoke, dust, pollens etc. When we inhale these particles get trapped in the hair present in our nasal cavity. However, sometimes these particles may get past the hair present in our 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. 

Q.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

Solution: A-(iii) B-(ii) C-(ii) D-(ii)

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

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

Solution:  (a)-iii (b)-iv (c)-I (d)-v (e)-ii (f)-vi

Q.7: Mark true (T) and false (F)
     (i)    During heavy exercise the breathing rate of a person slows down.
    (ii)    Plants carry out photosynthesis only during the day and respiration only at night.
   (iii)    Frogs breathe through their skins as well as their lungs.
  (iv)    The fishes have lungs for respiration.
   (v)    The size of the chest cavity increases during the inhalation.
Solution:  (i)F (ii)F (iii)T (iv)F (v)T

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