The mechanism of photosynthesis takes places two sequential stages:
  1. The light dependent reactions and
  2. The light-independent reactions (C3 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 \(1939\).
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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:
Adenosine Triphosphate
Adenosine Diphosphate
Nicotinamide Adenine Dinucleotide
Nicotinamide Adenine Dinucleotide phosphate
Nicotinamide Adenine Dinucleotide phosphate (reduced form)
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