The Function of Chlorophyll

In the diagram at the left, notice the chlorophyll in the leaves. It is the substance that gives plants their green colour. But that's not its primary role!

Chlorophyll is a catalyst in the reaction that uses water and carbon dioxide to produce glucose and oxygen.

Without chlorophyll, a plant would not be able to absorb energy from sunlight, no matter how much water and nutrients it gets. That is why photosynthesis happens only in green plants.