Question

Which of the following statements are correct about photosynthesis
(A). Photosystem I has a greater number of a particular type of chlorophyll molecule called chlorophyll a
(B). Photosystem II is maximally activated at wavelengths shorter than 680 nm
(C). In photosystem I, NADPH is produced.
(D). Photosystem II is maximally activated at wavelengths larger than 680 nm
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (A), (B), (C) and (D).
• D. (B), (C) and (D) only.

Hint:

A key distinction to remember: PSII (P680) initiates electron flow by splitting water and is sensitive to wavelengths \(\leq\) 680 nm. PSI (P700) is the terminal system in linear flow, leads to NADPH production, and can use light of wavelengths \(\leq\) 700 nm, including far-red light (>680 nm) which PSII cannot efficiently use.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
This question assesses knowledge about the light-dependent reactions of photosynthesis, specifically the roles and properties of Photosystem I (PSI) and Photosystem II (PSII).
Step 2: Detailed Explanation:
Let's analyze each statement:
(A) Photosystem I has a greater number of a particular type of chlorophyll molecule called chlorophyll a: Both photosystems are rich in chlorophyll a. While the total number of chlorophyll molecules might be similar or even higher in PSII, PSI has a significantly higher ratio of chlorophyll a to chlorophyll b compared to PSII. In this context, the statement is generally considered correct as it emphasizes the prominence of chlorophyll a in PSI.
(B) Photosystem II is maximally activated at wavelengths shorter than 680 nm: The reaction center of PSII is called P680 because it has a peak absorption at 680 nm. It utilizes light with wavelengths of 680 nm or less. Therefore, it is maximally activated at wavelengths shorter than or equal to 680 nm. This statement is correct.
(C) In photosystem I, NADPH is produced: In the final step of the linear electron flow (non-cyclic photophosphorylation), high-energy electrons from PSI are passed to the enzyme Ferredoxin-NADP\(^+\) reductase (FNR), which then reduces NADP\(^+\) to NADPH. This statement is correct.
(D) Photosystem II is maximally activated at wavelengths larger than 680 nm: This is incorrect. The efficiency of PSII drops sharply for wavelengths longer than 680 nm (the "red drop" effect). Photosystem I (P700) is the one that can be activated by light of wavelengths longer than 680 nm (far-red light). This statement directly contradicts the properties of PSII.
Step 3: Final Answer:
Statements (A), (B), and (C) are correct descriptions of photosynthesis. Statement (D) is incorrect. Therefore, the correct option is the one that includes (A), (B), and (C) only.