Cyclic photophosphorylation

Definition

Cyclic photophosphorylation is a process in photosynthesis where electrons are recycled back to the photosystem, generating ATP without producing NADPH. This pathway helps balance the ATP/NADPH ratio during light-dependent reactions.

5 Must Know Facts For Your Next Test

1. Occurs primarily in Photosystem I.
2. Does not produce oxygen as water is not split.
3. Helps generate additional ATP needed for the Calvin cycle.
4. Involves only cyclic electron flow, meaning electrons return to the same photosystem after energy transfer.
5. Essential for organisms that rely on light for energy but have limited access to water.

Review Questions

• Which photosystem is involved in cyclic photophosphorylation?
• What molecule is predominantly produced during cyclic photophosphorylation?
• Why is cyclic photophosphorylation important for balancing cellular energy needs?

Related terms

Photosystem I: A protein complex used in the light-dependent reactions of photosynthesis that absorbs light and initiates electron transport.

Non-cyclic Photophosphorylation: A process in which electrons travel from water to NADP+ via both Photosystems II and I, producing NADPH and ATP.

Calvin Cycle: A set of chemical reactions that take place in chloroplasts during photosynthesis, using ATP and NADPH to synthesize organic compounds.