Light and Dark Reactions

Light and Dark Reactions

Photosynthesis involves two main stages: light-dependent reactions and light-independent (dark) reactions.


  • Light-Dependent Reactions:

- Occur in the thylakoid membranes of chloroplasts.

- Light energy is absorbed by chlorophyll, initiating electron transfer.

- Water molecules are split, releasing oxygen, protons, and electrons.

- Electron transport chains generate ATP and NADPH.

- ATP and NADPH are energy carriers used in the dark reactions.


  • Dark Reactions (Calvin Cycle):

- Occur in the stroma of chloroplasts.

- Utilize ATP and NADPH produced in the light-dependent reactions.

- Carbon dioxide is fixed into organic molecules, facilitated by the enzyme Rubisco.

- Organic molecules are synthesized, including glucose, through a series of enzymatic steps.

-Regeneration of RuBP ensures the continuous operation of the cycle.