NCERT Class 11 Science — Chapter 1: Photosynthesis in Higher Plants

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For the synthesis of one molecule of glucose via the Calvin cycle, which one of the following represents the correct requirement?

Official previous-year question

Verified 1 Aug 2026.

Options

A12 turns and 36 ATP and 24 NADPH
B6 turns and 18 ATP and 12 NADPH
C3 turns and 9 ATP and 6 NADPH
D6 turns and 12 ATP and 12 NADPH

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Solution

Correct Option

The correct option is 6 turns and 18 ATP and 12 NADPH.

Explanation

The Calvin cycle (or C₃ cycle) is the light-independent reaction of photosynthesis that takes place in the stroma of chloroplasts. It fixes atmospheric carbon dioxide (CO₂) to synthesize sugars. The cycle consists of three main stages: Carboxylation, Reduction, and Regeneration.

Stoichiometric Analysis

To synthesize one molecule of glucose (C₆H₁₂O₆), which contains 6 carbon atoms, the cycle must fix 6 molecules of CO₂. Since one turn of the Calvin cycle fixes one molecule of CO₂, the cycle must turn 6 times.

The energy requirements for a single turn (fixing 1 CO₂) are as follows:

Reduction Stage: Requires 2 molecules of ATP and 2 molecules of NADPH for the reduction of 3-phosphoglycerate.
Regeneration Stage: Requires 1 molecule of ATP for the regeneration of Ribulose-1,5-bisphosphate (RuBP).
Total per turn: 3 ATP and 2 NADPH.

Therefore, for the synthesis of one glucose molecule (6 turns):

Total ATP: 6 turns × 3 ATP/turn = 18 ATP
Total NADPH: 6 turns × 2 NADPH/turn = 12 NADPH

Key Takeaway: The synthesis of one molecule of glucose requires 6 turns of the Calvin cycle, consuming a total of 18 ATP and 12 NADPH molecules.

Your note

More from Chapter 1: Photosynthesis in Higher Plants

Consider the following statements about autotrophic nutrition: 1. It is characteristic of green plants and some bacteria. 2. It involves conversion of chemical energy into light energy. 3. Heterotrophs ultimately depend on it. Which of the statements given above are correct?

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Assertion (A): In aquatic plants, bubbles of oxygen are formed around the green parts during active photosynthesis. Reason (R): Photosynthesis requires light energy to split water molecules, releasing oxygen.

hard

With reference to Julius von Sachs’ contributions, consider the following statements: 1. Photosynthetic products are stored primarily as proteins. 2. Chlorophyll is confined to distinct cellular bodies. 3. Non-green parts are not involved in carbohydrate synthesis. Which of the statements given above is/are correct?

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Consider the following statements about oxygen evolution in photosynthesis: 1. It is always replaced by sulphur production in all autotrophs. 2. It arises from the oxidation of water. 3. It is derived from carbon dioxide in higher plants. Which of the statements given above is/are correct?

hard

With reference to the role of photosynthesis in the biosphere, consider the following statements: 1. It is responsible for releasing carbon dioxide into the atmosphere. 2. It is the primary source of food for all living forms. 3. It is the only pathway of ATP generation in plants. Which of the statements given above is/are correct?

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Correct Option

The correct option is 6 turns and 18 ATP and 12 NADPH.

Explanation

Stoichiometric Analysis

The energy requirements for a single turn (fixing 1 CO₂) are as follows:

Reduction Stage: Requires 2 molecules of ATP and 2 molecules of NADPH for the reduction of 3-phosphoglycerate.
Regeneration Stage: Requires 1 molecule of ATP for the regeneration of Ribulose-1,5-bisphosphate (RuBP).
Total per turn: 3 ATP and 2 NADPH.

Therefore, for the synthesis of one glucose molecule (6 turns):

Total ATP: 6 turns × 3 ATP/turn = 18 ATP
Total NADPH: 6 turns × 2 NADPH/turn = 12 NADPH

Key Takeaway: The synthesis of one molecule of glucose requires 6 turns of the Calvin cycle, consuming a total of 18 ATP and 12 NADPH molecules.