NCERT Solutions for Class 7th Science Chapter 10 .2.2 Role of air in the preparation of food — Activity 10.5: Let us explore
Book page 14510 Updated on2026-09-19
Q1.
In Fig. 10.4, set-up A is placed in sunlight, and set-up B is placed in the dark. What difference do you observe in the two set-ups?
Fig. 10.4, page 145 — set-up A is placed in sunlight and set-up B is placed in the dark.
Answer
Both set-ups are identical — a water plant under an inverted funnel in a beaker of water, with an inverted test tube full of water over the funnel stem. Only the light is different.
Set-up
Kept in
What you see
A
Sunlight
A steady stream of air bubbles rises from the water plant, passes up the funnel stem and collects as gas in the inverted test tube, pushing the water level down
B
The dark
No bubbles. The test tube stays full of water; no gas collects
Why the funnel and the inverted test tube: the funnel gathers every bubble rising from the plant and channels it into one narrow stream, and the water-filled inverted test tube traps that gas so it can be collected and tested later.
Q2.
Do you observe air bubbles emerging in the inverted test tube in set-up A?
Answer
Yes. In set-up A, kept in sunlight, bubbles rise continuously from the leaves of the water plant, travel up through the funnel and gather in the inverted test tube.
They appear only in A. In set-up B, kept in the dark, no bubbles form — because photosynthesis occurs in the presence of sunlight, and no gas is being produced.
Try This: use a fresh sprig of hydrilla and place set-up A near a sunny window. Count the bubbles per minute, then shade the beaker partly with cardboard and count again. The rate falls as the light falls.
Q3.
The gas produced in this set-up caused bubbles to emerge and get accumulated in the inverted test tube. Which gas is this?
Answer
It is oxygen.
Barkha didi proved it. When enough gas had collected, she closed the mouth of the inverted test tube with her thumb, lifted it off the set-up, and quickly inserted a lit matchstick into it. The matchstick produced an intense flame.
Why the flame flares up: oxygen supports burning. A glowing or small flame becomes bright and intense in gas rich in oxygen. That is the standard test for oxygen — and it also rules out carbon dioxide, which would have put the flame out.
Conclusion: oxygen is released during photosynthesis, and photosynthesis takes place in the presence of sunlight.