Question

The photosynthesis in a plant is not taking place during the day time if the plant is releasing:
(a) water vapour
(b) oxygen
(c) carbon dioxide
(d) all the above

Answer 1

(c) carbon dioxide
During daytime, the carbon dioxide produced through respiration is used up in photosynthesis by leaves. In fact, more carbon dioxide is taken in from the air for this purpose.
So, oxygen is diffused out and carbon dioxide is diffused in.

Hence, if a plant is releasing carbon dioxide during the daytime, then photosynthesis is not taking place.