# CBSE NCERT Solutions for Class 7 Science Chapter 10

Refer NCERT solutions while you study, it will help you at the time of revision. NCERT solutions will also help students to retain the information for a longer period of time.

CBSE NCERT Solutions for Class 7 Science Chapter 10:

Question-1:

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

Solution:

Sneezing expels the foreign particles from the inhaled air, so that only clean
air enters our body. These particles get trapped in the nasal cavity and irritate the lining of the cavity which results in sneezing.

Question-2:

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?

Solution:

Test-tube A will have the highest concentration of CO2 because snail will take
in oxygen and gives out CO2 during respiration. In test-tubes B and C, the CO2 will be utilized by the water plant for synthesizing food through photosynthesis and hence there will be lesser concentration of CO2 in these.

Question-3:

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.

Solution:

The mountaineers carry oxygen with them because
(b) The amount of air available to a person is less than that available on the ground.

Question-4:

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

Solution:

During the run, the demand of energy is high but the supply of oxygen to produce
energy is limited. Therefore, anaerobic respiration takes places in the muscle cells to fulfil the demand of energy. After finishing the race, an athlete breathes faster and deeper than usual so that more oxygen is supplied to the cells.