Question

How are light-dependent and light-independent reactions of photosynthesis related?

Answer 1

Hint: The photosynthesis process completes in two steps- light reaction and dark reaction. Light reaction is also called the photochemical phase and it occurs in thylakoids whereas the dark reaction is called the thermochemical phase and it occurs inside the stroma of chloroplast.

Complete answer:
Light reaction begins as soon as the light falls on the green plants. The pigment molecules present in PS-I and PS-II that are located inside the thylakoids absorb their specific wavelength of light and become energized. The accessory pigments absorb light and transfer their absorbed energy finally to their reaction centre that takes part in the photochemical process. The two photosystems are connected in series with each other by the components of the electron transport chain. The reaction centre becomes so excited that they escape high energy electrons which move to nearby electron acceptor molecules. The electrons move through two pathways cyclic and noncyclic. The assimilatory power i.e. ATP and NADPH generated in the light reaction is used in the synthesis of carbohydrates in the dark reaction.
In the dark reaction the products of light reaction or assimilatory power are used to incorporate carbon from carbon dioxide to carbohydrate. Although the reaction itself does not require light but the process usually occurs in the light and continues for a very brief period after a plant is kept in dark till NADPH and ATP are available.

Note: Carbon dioxide fixation in dark reaction was thoroughly worked out by M. Calvin. Therefore, the complete pathway is called Calvin cycle. The first stable product of Calvin cycle is a three carbon so compound the cycle is also called C3 cycle