Calvin Cycle NEET 2026: Turns for Three Glucose Molecules

What is the answer to the Calvin cycle NEET 2026 three-glucose question?

Correct option: D, 18 turns. In this Calvin cycle NEET 2026 question, each turn fixes one carbon dioxide molecule, so three six-carbon glucose equivalents require eighteen turns. It is from Biology, the 2026-06-21 re-held paper, Code-50. Medium difficulty is the question bank’s classification, not an official NTA rating.

To synthesise three glucose molecules, how many times must the Calvin cycle turn?

What does one turn of the Calvin cycle count?

One turn fixes one carbon dioxide molecule. The Calvin cycle is the biosynthetic phase of photosynthesis. RuBisCO catalyses the carboxylation of RuBP, the carbon dioxide acceptor. Reduction and regeneration follow, allowing the acceptor to participate again.

NCERT Class 11 Biology’s Photosynthesis in Higher Plants chapter provides the conceptual basis. The counting rule is:

1 turn ⟷ 1 C O_{2} fixed

Regeneration lets the carbon dioxide acceptor participate again; it does not mean a glucose molecule has been completed. For this calculation, glucose represents a hexose-equivalent output, containing six carbon atoms. The immediate net carbohydrate output is triose phosphate, represented here by G3P, which contains three carbon atoms.

A pathway shown for three carbon dioxide molecules therefore represents three turns, not one turn. Distinguish the amount shown in the pathway from the definition of a turn.

How do you calculate the turns needed for three glucose molecules?

One glucose equivalent requires six turns, so three require eighteen. Follow the supplied solution’s carbon-counting method: count the carbon atoms needed, match them to fixed carbon dioxide, then convert that count into turns. ATP and NADPH are unnecessary for answering this question.

Glucose has the formula: $C_{6} H_{12} O_{6}$

Each glucose molecule contains six carbon atoms. Each fixed carbon dioxide molecule contributes one carbon atom, so one glucose equivalent requires six carbon dioxide molecules.

6 C O_{2} \times \frac{1 turn}{1 C O_{2}} = 6 turns

Scale the per-glucose requirement:

3 glucose equivalents \times \frac{6 turns}{1 glucose equivalent} = 18 turns

Check by carbon balance:

3 \times 6 = 18 carbon atoms ⟷ 18 C O_{2} fixed

The net-output comparison is:

Three turns: one net G3P.
Six turns: two net G3P, equivalent to one glucose.
Eighteen turns: six net G3P, equivalent to three glucose molecules.

Both calculations give option D, 18. Count fixed carbon dioxide molecules, not completed glucose molecules, when counting turns.

Why is option A, six turns, wrong?

Six turns is correct for one glucose molecule, not three. Option A is a valid intermediate result, but stopping there leaves out multiplication by the three glucose molecules requested.

The incomplete calculation is: $1 glucose equivalent ⟶ 6 turns$

The completed calculation is:

3 glucose equivalents ⟶ 3 \times 6 = 18 turns

Write “turns per glucose” beside the intermediate result and retain that label until the multiplication is complete. Use this instead of a bare “6”: the label distinguishes the per-glucose requirement from the total number of turns.

How many Calvin-cycle turns give one net G3P?

Three turns give one net G3P, so the answer is option B. G3P has three carbon atoms. These require three fixed carbon dioxide molecules, with one molecule fixed per turn.

Original related practice from the same Plant Physiology chapter, not another verified PYQ:

How many Calvin-cycle turns are needed for a net gain of one G3P molecule?

3 C O_{2} \times \frac{1 turn}{1 C O_{2}} = 3 turns

Net means available after the cycle’s regeneration requirements are met, not every intermediate formed during the pathway. Three turns yield one net G3P; six turns yield two net G3P, enough carbon for one glucose equivalent.

How many turns and glucose equivalents correspond to twelve fixed carbon dioxide molecules?

Twelve fixed carbon dioxide molecules correspond to twelve turns and two glucose equivalents, option C. The number of turns equals the number of carbon dioxide molecules fixed. Finding glucose equivalents requires division because each glucose contains six carbon atoms.

Original related practice, not an attributed exam question:

Fixation of twelve carbon dioxide molecules through the Calvin cycle corresponds to how many turns and how many glucose equivalents?

Turns = 12 C O_{2} \times \frac{1 turn}{1 C O_{2}} = 12 turns

Glucose equivalents = \frac{12 C O_{2}}{6 C O_{2} per glucose equivalent} = 2

Turns and glucose molecules are different quantities. Calculate and label them separately.

How much ATP and NADPH do three glucose equivalents require?

One glucose equivalent requires 18 ATP and 12 NADPH, so three require 54 ATP and 36 NADPH, option D. The supplied solution writes the reducing cofactor as: $N A D P H_{2}$

Original related practice, not another verified PYQ:

What are the Calvin-cycle ATP and NADPH requirements for three glucose equivalents?

Multiply each requirement separately: $ATP required = 3 \times 18 = 54$ $NADPH required = 3 \times 12 = 36$

These are Calvin-cycle requirements, not an accounting of every process in photosynthesis. Label the requested quantity first, then use the reusable rule:

For n glucose equivalents: turns = 6 n, ATP = 18 n, NADPH = 12 n

Next step: the past-paper archive on NEET JEEnius AI and search past NEET papers by year, subject or chapter, each with a worked solution (100 free searches a month).

Keep going with Equilibrium NEET 2006: Dilute HCl and Water Ionisation.

Frequently asked questions

How many Calvin-cycle turns are needed for three glucose molecules?

Three glucose equivalents require 18 Calvin-cycle turns, making option D correct. Each glucose contains six carbon atoms, and each turn fixes one carbon dioxide molecule. Six turns cover only one glucose equivalent; multiply by three to get 18.

What counts as one turn of the Calvin cycle?

One turn of the Calvin cycle fixes one carbon dioxide molecule. A pathway diagram showing fixation of three carbon dioxide molecules therefore represents three turns, not one. Regeneration of the carbon dioxide acceptor does not mean a glucose molecule has been completed.

How many Calvin-cycle turns produce one net G3P?

Three turns produce one net G3P molecule, which contains three carbon atoms. Net output means the amount available after the cycle's regeneration requirements are met. Six turns produce two net G3P molecules, equivalent in carbon content to one glucose.

How much ATP and NADPH are needed for three glucose molecules?

The Calvin cycle requires 54 ATP and 36 NADPH for three glucose equivalents. One glucose equivalent requires 18 ATP and 12 NADPH, so multiply each requirement by three. These figures cover Calvin-cycle requirements, not every process in photosynthesis.

Calvin Cycle NEET 2026: Three Glucose Require 18 Turns