Topic: Light reactions, cyclic and non-cyclic photophosphorylation, chemiosmosis· Plant Physiology

In a chloroplast the highest number of protons are found in :

1. Stroma

2. Lumen of thylakoids

3. Inter membrane space

4. Antennae complex

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Answer: 2. Lumen of thylakoids

Key idea: During the light reactions, protons build up inside the thylakoid lumen.

They come from water splitting in the lumen and from plastoquinone pumping H⁺ from the stroma into the lumen. The proton gradient then drives ATP synthase, so protons flow back to the stroma. Hence the lumen has the highest proton count, while the stroma has fewer.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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In a chloroplast the highest number of protons are found in :

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