Question

Which one of the following statements regarding plant Photosystems is NOT true?

• A. Photosystem I is present in unstacked thylakoid membrane
• B. Photosystem II is present in stacked thylakoid membrane
• C. Photosystem I absorbs light of \(700\) nm wavelength
• D. Photosystem I is responsible for water splitting

Hint:

Remember: \[ PSI \rightarrow P_{700}, \qquad PSII \rightarrow P_{680} \] and water splitting occurs only in Photosystem II.

Answer 1

The Correct Option is D

Step 1: Understand photosystems in plants.
Photosystems are pigment-protein complexes present in the thylakoid membranes of chloroplasts. They play a central role in the light reactions of photosynthesis.

Step 2: Analyze Photosystem I location.
Photosystem I (PS I) is mainly located in the unstacked regions of thylakoid membranes, also known as stroma lamellae. Therefore, statement (A) is correct.

Step 3: Analyze Photosystem II location.
Photosystem II (PS II) is mainly present in the stacked thylakoid membranes called grana. Hence, statement (B) is correct.

Step 4: Analyze wavelength absorbed by PS I.
The reaction center chlorophyll of Photosystem I is known as \(P_{700}\) because it absorbs light maximally at approximately \(700\) nm wavelength. Therefore, statement (C) is correct.

Step 5: Understand water splitting.
Water splitting or photolysis occurs in Photosystem II, not in Photosystem I. PS II contains the oxygen-evolving complex responsible for breaking water molecules into electrons, protons, and oxygen.

Step 6: Identify the incorrect statement.
Since water splitting is performed by PS II and not PS I, statement (D) is false.

Step 7: Final conclusion.
Therefore, the statement that is NOT true is
\[ \boxed{\text{Photosystem I is responsible for water splitting}} \]
Hence, the correct answer is option (D).