Paper 1 · People, Development and Environment
The balance in oxygen level is maintained by
APhotosynthesis and cellular respiration ✓ Correct
BIndustrial emissions of gases
CRelease of ozone in the upper atmosphere
DPhotochemical smog
Correct answer: (A) Photosynthesis and cellular respiration — The oxygen balance is maintained by photosynthesis and cellular respiration, so that is the answer.
Explanation
★The oxygen balance is maintained by photosynthesis and cellular respiration, so that is the answer.
★Plants release oxygen during photosynthesis.
★Living things use up oxygen during cellular respiration.
★These two opposite processes keep the oxygen level balanced.
★Industrial emissions and smog disturb the air rather than balance oxygen.
★So the answer is photosynthesis and cellular respiration.
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