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Biology Question 107 – NEET-UG 2024

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Which of the following are required for the dark reaction of photosynthesis? A. Light B. Chlorophyll C. CO2 D. ATP E. NADPH Choose the correct answer from the options given below:

Recall that photosynthesis consists of two main stages: the light-dependent reactions and the light-independent reactions (dark reaction or Calvin cycle).

Step 1: Understand the Dark Reaction (Calvin Cycle)✦ Active

The dark reaction, also known as the Calvin cycle, is the light-independent stage of photosynthesis. Its primary function is to fix atmospheric carbon dioxide (CO2) and convert it into glucose using the energy and reducing power generated during the light-dependent reactions.

Step 2: Identify Direct Requirements for the Dark Reaction○ Expand

For the Calvin cycle to proceed, it directly requires: - Carbon dioxide (CO2): As the carbon source for sugar synthesis. - ATP: Provides the energy for various steps in the cycle. - NADPH: Provides the reducing power (electrons) to convert 3-phosphoglycerate into glyceraldehyde-3-phosphate. Light and chlorophyll are essential for the light-dependent reactions that produce ATP and NADPH, but they are not directly consumed or involved in the dark reaction itself.

💡 Teacher's Secret Hint

Distinguish between direct requirements for the dark reaction and indirect requirements (like light and chlorophyll) that are needed for the light reactions to produce the dark reaction's inputs.

Step 3: Match Requirements to Options○ Expand

Based on the direct requirements, C (CO2), D (ATP), and E (NADPH) are needed for the dark reaction. Therefore, option (2) 'C, D and E only' is the correct answer.

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