Photosynthesis Question 2

2. In a chloroplast the highest number of protons are found in

[2016]

(a) stroma

(b) lumen of thylakoids

(c) inter membrane space

(d) antennae complex

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Answer : b

Hints & Solution

(b) Proton concentration is higher in the lumen of thylakoid due to photolysis of water, $H^{+}$pumping and NADP reductase activity in stroma. During the light-dependent reaction, protons are pumped across the thylakoid membrane into the lumen making it acidic down to $pH 4$. The light - included electron transfer in photosynthesis drives protons into the thylakoid lumen. The excess protons flow out of the lumen through ATP synthase to generate. ATP in the stroma.