### Theory:

The mechanism of photosynthesis takes places two sequential stages:
1. The light dependent reactions and
2. The light-independent reactions (${C}_{3}$ cycle or Calvin cycle).
As we have learnt, the process of photosynthesis and its various stages occurs inside the chloroplast. Hence, the structural organization of chloroplast is in such a way that the light-dependent
(Light reaction) and light-independent (Dark reaction) occur at different sites in the chloroplast.

Picture indicating the sites of light and dark reactions
1. Light dependent reactions (Hill reaction/Light reaction):
It is also known as Hill reaction as it was discovered by Robin Hill in the year $$1939$$.

Light reactions
• Light-dependent processes occur in the thylakoid membranes (grana) of the chloroplasts and require a constant source of light energy.
• The overall goal of these reactions is to transform light energy into chemical energy.
• Hence, in these reactions, the photosynthetic pigments absorb the light energy and convert it into
chemical energy ATP and $$NADPH_2$$.
• These light reaction products pass from the thylakoid to the stroma of the chloroplast.
Abbreviations to know: