During light reaction photolysis of water take place which releases hydrogen ion and thes are instantly go no of changes in dark reaction
in dark reaction h2 ions picked up by NADP to form NADPH2...
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Source of Protons for NADP+ Reduction to NADPH
Protons are essential for the reduction of NADP+ to NADPH in the light-dependent reactions of photosynthesis. These protons are derived from various sources within the thylakoid membrane of chloroplasts.

Water Splitting
- The primary source of protons for NADP+ reduction is the process of water splitting during the light-dependent reactions.
- Water molecules are split by the enzyme complex known as photosystem II, releasing protons, electrons, and oxygen.

Proton Pumping
- Another source of protons is through the movement of protons across the thylakoid membrane by the electron transport chain.
- As electrons move through the chain, protons are pumped from the stroma into the thylakoid lumen, creating a proton gradient.

ATP Synthase
- Protons that accumulate in the thylakoid lumen due to water splitting and proton pumping are then used by ATP synthase to generate ATP.
- This process, known as chemiosmosis, also helps maintain the proton gradient necessary for NADP+ reduction.

NADP+ Reduction
- Finally, the protons generated from water splitting, proton pumping, and ATP synthase are combined with electrons from photosystem I to reduce NADP+ to NADPH.
- This reduction reaction is catalyzed by the enzyme ferredoxin-NADP+ reductase, producing NADPH, which is a crucial molecule for the Calvin cycle.
In summary, protons are sourced from water splitting, proton pumping, and ATP synthase within the thylakoid membrane to facilitate the reduction of NADP+ to NADPH during photosynthesis.