السؤال 58

Near dusk there is a moment when a plant's rate of photosynthesis exactly equals its rate of respiration. What can be said about its exchange of gases with the air at that moment?

Nothing is happening inside the plant at all
Both processes have stopped, which is why the rates match
There is no net exchange, though both processes continueالإجابة الصحيحة
The plant releases oxygen twice as fast as before

الشرح

Each process uses what the other produces, so when their rates match, whatever one releases is taken up by the other as fast as it appears and nothing needs to cross the leaf surface. That is a balance rather than a standstill, and the cells are as busy then as at any other time of day.

الشرح

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