Also in that chamber there are the chloroplasts.
The light required is absorbed by a green pigment called chlorophyll in the leaves.
Plants store energy through the endothermic reactions of photo- synthesis.
It may involve a single chemical reaction or a series of chemical reaction.
In simple terms, the endothermic reactions absorb energy from the surrounding that is in the form of heat.
Example: When carbon reacts with oxygen, it produces carbon dioxide and heat energy.
That creates a pressure that will make rotate the stomates, and at their full rotation there is an aperture, very small.
While, the exothermic reaction releases energy into the surrounding from the system.