Question

To reduce 1 CO2, in C3 cycle, assimilatory power
needed is
(1) ATP, 2NADPH + H+.
(2) 2ATP, 3NADPH + H+
(3) 5ATP, 2NADPH + H+
(4) 6.5ATP, 2NADPH+H+​

Answer 1

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Correct Answer : (1) ATP, 2NADPH + H+.

Answer 2

Answer:

Calvin cycle is also called dark reaction that uses products of light reaction called NADPH and ATP to fix carbon dioxide. Therefore, to reduce 1 molecule of carbon dioxide in the C3 cycle, 2ATP and 3NADPH + H+ are required.

Explanation:

• In the plant cell, there are 5 carbon components, so the carbon dioxide from the air is combined with 5 carbon components present in the plant cell and converted into 6 carbon components, but the 6-carbon component is not that stable so it immediately split into 3 carbon component which is a relatively first stable component of the photosynthesis, that is why Calvin cycle is also called C3 pathway.

• There are 3 basic stages in the Calvin cycle called fixation, reduction, and regeneration. There are 2 chemicals present in the Calvin cycle, an enzyme RuBisCO and RuBP or ribulose biphosphate molecule. RuBP is categorized by 5 carbon atoms and a phosphate group on each end.

• The reaction between carbon dioxide and RuBP is catalyzed RuBisCO leading to the formation of 6 carbon compound which is immediately converted into 3 carbon compound, this process is termed carbon fixation because carbon dioxide is fixed from its inorganic form to organic form.

• Then in the reduction reaction- Energy stored by ATP and NADPH is used to convert 3 carbon-compound or 3-PGA into G3P (another carbon compound) as the gain of electrons occurs. Then ADP and NADP+ return to the light-dependent reactions to re-energize. 1 of the G3P molecules leaves the Calvin cycle to contribute to the formation of a carbohydrate molecule called glucose.
• Because carbohydrate molecule contains 6 carbons, it takes 6 turns of the Calvin cycle to fix 6 carbon atoms from CO2. These six turns require energy input from 12 ATP molecules and 12 NADPH molecules in the reduction step and 6 ATP molecules in the regeneration step. Therefore, by this, we can say that 2ATP and 3NADPH + H+ are required to convert 1 carbon dioxide molecule.