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UPSC Prelims 1982 · Environment · Pollution Files
Ozone present in the ozone layer of the atmosphere is important because
- (a) It gives oxygen on dissociation
- (b) It shields other gases
- (c) It helps in the growth of the plants by absorbing a large proportion of the sun's ultraviolet radiations
- (d) None of these
Show the answer and explanation
Answer: (c) It helps in the growth of the plants by absorbing a large proportion of the sun's ultraviolet radiations
By absorbing most of the sun’s UV, the ozone layer protects plants (and all life) — UV damages leaves and DNA.
The idea
Ultraviolet light breaks DNA and proteins. Early life could survive only under water, which blocks UV. When photosynthesis filled the air with oxygen, an ozone layer formed, and only then could plants and animals live on land. That is the real importance of ozone for plants and all other life.
Photosynthesis releases oxygen → Oxygen builds up in the air → UV turns some of it into ozone → Ozone layer blocks harmful UV → Life moves from water to land
Why the others are wrong
(a) Ozone breaking apart gives oxygen, but that is not why it matters.
(b) It doesn’t shield other gases.
The trap
The wording “helps plant growth” is odd, but it points to UV protection — the real reason.
Also know
Extra UV-B reduces the growth and yield of crops and kills phytoplankton, the base of the ocean food chain. Oxygen released when ozone breaks up is tiny in amount and is not the reason the layer matters.
🔒 Ozone layer → blocks UV → protects DNA of plants and animals.
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