Question

How first law of thermodynamic applied in the process of photosynthesis?

Answer 1

The first law of thermodynamics states that "energy cannot be created or destroyed."

This applies to photosynthesis as energy isn't being created or destroyed during the process of photosynthesis. As the light reactions take place, the energy from the photons are used to 'excite' the electrons in both photosystem 1 and 2. This energy is used later to convert NAD+ to NADPH

So the energy is conserved!