Question

From a photosynthetic perspective, explain why plants need water. In other words, where in the plant cell and when is what used during photosynthesis.

Answer 1

In photosynthesis, the total reactions are classified as light reactions (light dependent reactions) and dark reactions (light independent reactions). All these reactions occur in chloroplast of the cell. During the light reactions the assimilatory power i.e. ATP and NADPH will be synthesized.

So, in the light reactions, when the sunlight hits the reaction center of photosystem I, it excites and releases electrons, these electrons passes through electron carriers. Later again after the sunilght hits the reaction center of photosystem II, again it releases the electrons, these will fill electron gaps of PS I reaction center. To fill the gap at reaction center of PS II, the hydrolysis the water takes place at OEC complex. The water produces 1/2O2, 2Protons and two electrons during hydrolysis. The oxygen will be released in to the atmosphere through stomata, those protons moves to stroma from lumen, and these two electrons transfer reaciton centre of the ps II.

This is the main role of water in photosynthesis.