In a chloroplast the highest number of protons are found in:
Answer: (B) Lumen of thylakoids. During the light reaction the splitting of water occurs on the inner side of the thylakoid membrane, so the protons released accumulate within the thylakoid lumen; additional protons are also pumped into the lumen and removed from the stroma during electron transport and NADP+ reduction.
- A.Stroma
- B.Lumen of thylakoids✓
- C.Inter membrane space
- D.Antennae complex
Correct Answer
(B) Lumen of thylakoids
Solution & Explanation
During the light reaction the splitting of water occurs on the inner side of the thylakoid membrane, so the protons released accumulate within the thylakoid lumen; additional protons are also pumped into the lumen and removed from the stroma during electron transport and NADP+ reduction. This makes the lumen the compartment with the highest proton concentration (lowest pH). Therefore the highest number of protons is found in the lumen of thylakoids (B), not the stroma. NCERT: Class 11 Ch 11, p.140 [140:040–140:042]: "the splitting of water accumulate within the lumen of the thylakoids."