Q.34 Which of the following are NOT true for photosynthesis?
(A) Reduction of CO2 and H2O
(B) Oxidation of CO2 and H2O
(C) Reduction of CO2 and oxidation of H2O
(D) Oxidation of CO2 and reduction of H2O
Photosynthesis involves the oxidation of water (H2O) and reduction of carbon dioxide (CO2) to produce glucose and oxygen. The correct answer to the question “Which of the following are NOT true for photosynthesis?” is options (A), (B), and (D), as only (C) accurately describes the redox processes.
Option Analysis
Photosynthesis is an oxidation-reduction (redox) reaction where specific molecules undergo distinct changes.
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(A) Reduction of CO2 and H2O: Incorrect. CO2 undergoes reduction to form carbohydrates, but H2O is oxidized, not reduced.
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(B) Oxidation of CO2 and H2O: Incorrect. CO2 is reduced, while H2O is oxidized—both processes do not involve oxidation.
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(C) Reduction of CO2 and oxidation of H2O: Correct. This matches the light-dependent reactions (water splitting) and Calvin cycle (CO2 fixation).
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(D) Oxidation of CO2 and reduction of H2O: Incorrect. Reverses the actual processes; CO2 gains electrons (reduction), H2O loses them (oxidation).
Photosynthesis redox reaction CO2 H2O powers life on Earth through precise oxidation reduction processes. In this CSIR NET-focused guide, explore how plants convert light energy into chemical bonds via these reactions.
Light Reactions: H2O Oxidation
Water splits in photosystem II, releasing electrons, protons, and O2. This oxidation provides energy carriers like NADPH and ATP. The oxygen-evolving complex facilitates: 2H2O→O2+4H++4e−.
Dark Reactions: CO2 Reduction
CO2 fixes into RuBP, then reduces to glucose using NADPH. Carbon gains electrons: CO2+2H++4e−→(CH2O)+H2O. ATP drives this anabolic pathway.
Common MCQ Pitfalls
Exams test redox directionality. Reduction adds electrons (CO2 to sugar); oxidation removes them (H2O to O2). Options reversing this are false.
