(a) List the events in proper sequence that take place during the process of photosynthesis. OR (b) Explain in brief two ways by which leaves of a plant help in excretion.

(a) Sequential events during photosynthesis:

The following three events occur during the process of photosynthesis:

1. Absorption of light energy by chlorophyll.
2. Conversion of light energy to chemical energy and splitting of water molecules ($12\text{H}_2\text{O}$) into hydrogen and oxygen ($6\text{O}_2$).
3. Reduction of carbon dioxide ($6\text{CO}_2$) to carbohydrates (glucose, $\text{C}_6\text{H}_{12}\text{O}_6$).

Note: These steps do not necessarily take place one after the other immediately. For example, desert plants take up carbon dioxide at night and prepare an intermediate which is acted upon by the energy absorbed by the chlorophyll during the day.

OR

(b) Two ways by which leaves of a plant help in excretion:

1. Gaseous Waste Elimination: Excess oxygen ($O_2$) produced as a by-product of photosynthesis and carbon dioxide ($CO_2$) produced during respiration are expelled into the atmosphere through the stomatal pores present on the surface of the leaves.
2. Shedding of Senescent Leaves: Many plant waste products are stored in cellular vacuoles of the leaves. These leaves eventually turn yellow and fall off (shedding), thereby removing the accumulated wastes from the plant body.