Question

Why does xerophytic plant has a alteration in steps of photosynthetical process?

Answer 1

We know that exchange of gases and transpiration in plants takes place though stomata. 

Xerophytic plants live in extreme weather conditions. They need to survive on very low availability of water so, they have to store it.
They do so by closing their stomata during day as to prevent transpiration.

When the stomata is closed exchange of gases also can't take place.

Therefore, to ensure the availability of water and carbon-di-oxide, xerophytes go through alteration in steps of photosynthesis, and open their stomata at night for exchange of gases. 

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