## CORE INFORMATION\n✓ **Answer**: [B]\n## CONCEPT FRAMEWORK\n\t**Primary Concept**: Red Drop Effect and Photosystem function\n\t**Related Topics**: Photosynthesis, Photosystems I and II (PS I and PS II), Quantum Yield, Light Absorption, Chlorophyll, Far-red light\n\t**Prerequisites**: Knowledge of photosynthesis, the role of PS I and PS II, and the concept of quantum yield.\n## SOLUTION PATHWAY\n**Given Information**:\n\tThe question asks for the cause of the 'red drop' phenomenon.\n**Method & Steps**:\n\t1. **Recall the Red Drop Effect**: The red drop effect is a phenomenon where the quantum yield of photosynthesis decreases sharply when plants are exposed to far-red light (wavelengths longer than 680 nm).\n\t\tReasoning: This effect is not due to a decline in the quantum yield of red light itself, as mentioned in option A, but a specific issue that occurs in far-red light.\n\t2. **Understand the Roles of PS I and PS II**: PS II is more sensitive to red light than far-red light, while PS I can absorb both.\n\t\tReasoning: The red drop is primarily due to the inefficiency of PS II at far-red wavelengths, as PS II is needed to generate the electron flow for both PS I and PS II.\n\t3. **Analyze the Options**: Option B, 'Non-functioning of PS – II in far red-light', is the most accurate description of the red drop effect.\n\t\tReasoning: Option A is incorrect because it describes a general decline and not a specific effect. Option C is incorrect because red light doesn't inhibit PS I. Option D is incorrect because oxidation of chlorophyll is a normal part of the photosynthetic process, not a specific cause of the red drop.\n**Result**: The correct answer is option B.\n\t\tVerification: The red drop effect is a well-documented phenomenon, and its main cause is the inefficiency of PSII in far-red light.\n ## OPTION ANALYSIS\n[A] :x: Decline in quantum yield in separate beams of red-light. This is incorrect because the red drop is related to far-red light, not red light. The quantum yield isn't declining in red light, but in far-red light conditions.\n[B] ✓: Non-functioning of PS – II in far red-light. This accurately describes the primary reason for the red drop effect.\n[C] :x: Inhibitory effect of red-light on PS – I. Red light does not inhibit PS I; PS I functions in red and far-red light. The red drop is due to PS II issues.\n[D] :x: Oxidation of chlorophyll. While oxidation of chlorophyll is part of photosynthesis, it's not directly linked to the red drop phenomenon.\n ## LEARNING AIDS\n\t**Common Mistakes**:\n\t\t1.Confusing the role of red and far-red light: Students often confuse the effects of red light and far-red light. Remember that the red drop is related to far-red light.\n\t\t2.Misunderstanding PS I and PS II roles: It's important to know that PS II is more sensitive to red light and its inefficiency in far-red light leads to the red drop.\n\t**Quick Tips**:\n\t\t1.Think of 'red drop' as 'dropping efficiency in far red light.'\n\t\t2.Remember that PS II is the main player in the red drop effect.

The correct Option is "Non-functioning of PS – II in far red-light "

NEET Botany Photosynthesis in Higher Plants MCQs

Prepare for NEET Biology Photosynthesis in Higher Plants with MCQs & PYQs on NEET.GUIDE. Get free practice, previous year questions, and expert guidance to grasp light and dark reactions.

NEET Questions / Botany / Photosynthesis in Higher Plants