CBSE Class 10 Science 2020 · Paper 31/1/3 · Question 27(a)

(a) The gas released during photosynthesis is oxygen. It is evolved by the splitting of water molecules: light energy absorbed by chlorophyll is used to split water into hydrogen and oxygen; the hydrogen is used to reduce carbon dioxide to glucose, and the oxygen is released as oxygen gas, which leaves the leaf through the stomata. (b) Stomata are tiny pores present on the surface of leaves, through which the exchange of gases (during photosynthesis, carbon dioxide in and oxygen out) and the loss of water vapour take place; each pore is bounded by a pair of guard cells. The opening and closing of the stomata is a function of the guard cells: when water flows into the guard cells they swell and the stomatal pore opens; when the guard cells lose water they shrink and the pore closes.