Question

Consider the given equation \[ 2\mathrm{H_2O} \rightarrow 4\mathrm{H^+}+\mathrm{O_2}+4e^- \] Where does this reaction take place in the chloroplasts?

• A. Outer surface of the thylakoid membrane
• B. Inner surface of the thylakoid membrane
• C. In the stroma matrix
• D. Intermembrane space

Hint:

Photolysis of water occurs at \[ \boxed{\text{Photosystem II on the inner (lumen) side of the thylakoid membrane}.} \] The products are \[ \boxed{\mathrm{O_2,\ H^+,\ and\ electrons}.} \]

Answer 1

The Correct Option is B

Step 1: Identify the given reaction. The reaction \[ 2\mathrm{H_2O}\rightarrow4\mathrm{H^+}+\mathrm{O_2}+4e^- \] represents the \[ \boxed{\text{photolysis (splitting) of water}.} \] This reaction is catalysed by the oxygen-evolving complex (OEC) associated with Photosystem II.

Step 2: Recall the location of photolysis. Photolysis of water occurs on the \[ \boxed{\text{inner surface of the thylakoid membrane}} \] facing the thylakoid lumen. The released protons accumulate inside the lumen, helping to establish the proton gradient required for ATP synthesis.

Step 3: Choose the correct option. Hence, the correct option is \[ \boxed{(B).} \]