Page 89 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

2. Why do we get muscle cramps after heavy exercise?

Ans. During heavy exercises, the muscles do not get enough oxygen to meet energy
demands leading to anaerobic respiration. This process produces lactic acid that

accumulates in the muscles and contributes to cramps by irritating muscles.
3. Why do we sneeze?

Ans. When we inhale air, it contains dust particles and these particles get trapped in the

hair present in our nasal cavity. Sometimes, these particles may pass through the hair
and irritate the mucus lining of the nasal cavity and as a result, we sneeze. Sneezing

expels the foreign particles from the inhaled air and dust-free clean air enters our
body.

4. Whenever we feel drowsy or sleepy, we start yawning. Does yawning help us in any
way?

Ans. When our brain or body is tired, yawning helps us to revive ourselves. Yawning help

us to take in more oxygen into the blood and give out carbon dioxide from the blood.
It also cools the brain.

5. Write the function of stomata.
Ans. During respiration in plants, the exchange of gases take place through stomata which

are tiny pores on leaves. The exchange of gases takes place through the stomata by
the process of diffusion. The opening and closing of the stomata is controlled by the

turgidity of guard cells. Each stoma is surrounded by a pair of bean shaped guard

cells that open or close the stomatal pore for regulating gaseous exchange.
6. When do plants respire?

Ans. Plants respire throughout the day and also at night. In the daytime, the released
carbon dioxide is used by plants for photosynthesis. However at night, only carbon

dioxide is released into the atmosphere through stomata as no photosynthesis
occurs.

7. How do fishes breathe? Explain.

Ans. Fish breathe with the help of gills located on either side of their head. Gills are
respiratory organs made up of a number of comb like structures called gill filaments

that provide a large surface area for gaseous exchange and are rich in blood supply.
The fish takes in water from its mouth and pushes it out forcefully through its gills.

The blood capillaries in the gills absorb the oxygen dissolved in the water and move it
into the blood stream. The heart pumps the blood and then distributes this oxygen-

rich blood throughout the body. Simultaneously, the carbon dioxide in the blood
passes out through the gills into the water.

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