NCERT Solutions for Class 7th Science Chapter 10 .2.2 Role of air in the preparation of food — In-text Questions
Book page 14310 Updated on2026-09-08
Q1.
What else is essential for the preparation of food in plants? Let us find out.
Answer
So far the chapter has established water, sunlight and chlorophyll. The one raw material still missing is a gas from the air — carbon dioxide.
The complete list of requirements for photosynthesis is therefore:
Carbon dioxide — from the air, entering through the stomata
Water — absorbed by the roots and carried up by the xylem
Sunlight — the energy source
Chlorophyll — the green pigment that captures that energy
Activity 10.4 is designed to test the fourth item on this list.
Q2.
Which gas from the air is essential in the process of food preparation in plants?
Answer
Carbon dioxide.
Air is a mixture of gases — mainly nitrogen and oxygen, with a very small amount of carbon dioxide. Of these, it is carbon dioxide that the plant uses as a raw material and builds into glucose. It enters the leaf through the tiny pores called stomata.
How we know: in Activity 10.4, caustic soda inside the bottle absorbs the carbon dioxide around the enclosed half of a leaf. That half makes no starch, while the half outside — in the same sunlight, on the same plant, with the same chlorophyll and water — turns blue-black. The only difference between the two halves is carbon dioxide.