Q.107 Botany ⭐ 360° Option Elimination Active

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NEET 2023 Botany Question 107 Solution

Topic: Photosynthesis in Higher Plants · Official NTA Booklet Code G5

Question

How many ATP and NADPH are required for the synthesis of one molecule of Glucose during Calvin cycle?

✓

Verified Against NTA Final Answer Key

Option (3) : 18 ATP and 12 NADPH₂

📚 Photosynthesis in Higher Plants Easy

📋 Given Parameters & Problem Setup

Pathway Calvin Cycle (

C_3

pathway)

Target Product 1 molecule of Glucose (

C_6H_{12}O_6

)

CO2 Fixed 6 molecules of

CO_2

⚡

The 30-Second Exam Hall Shortcut: ⚡ 3:2 Ratio Multiplied by 6 Rule

⏱️ Save ~25 seconds

Fixing 1 $CO_2$ requires 3 ATP and 2 $NADPH$ . To synthesize 1 glucose ( $6 \text{ carbons}$ ), simply multiply the energetic cost by 6: $6 \times 3 = 18\text{ ATP}$ and $6 \times 2 = 12\text{ NADPH}$ !

1 Per

CO_2

fixed: 2 ATP in reduction + 1 ATP in RuBP regeneration = 3 ATP.

2 Per

CO_2

fixed: 2 NADPH in reduction = 2 NADPH.

3 For 1 glucose (

C_6H_{12}O_6

): 6 cycles required.

4 Total ATP =

6 \times 3 = 18\text{ ATP}

5 Total NADPH =

6 \times 2 = 12\text{ NADPH}_2

6 Select Option (3) 18 ATP and 12 NADPH2.

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Photosynthesis Calvin cycle biochemical stoichiometry.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Calvin Cycle Phases and Energy Consumption per CO2

For each single molecule of $CO_2$ entering the cycle, energy is consumed in two specific steps:

\begin{aligned} \text{\textbf{Reduction:}} & \quad 2\text{ molecules of 3-PGA} \xrightarrow{2\text{ ATP } + 2\text{ NADPH}} 2\text{ Triose-P} \\[4pt] \text{\textbf{Regeneration:}} & \quad \text{Triose-P} \xrightarrow{1\text{ ATP}} 1\text{ RuBP} \\[4pt] \hline \text{\textbf{Net per }} CO_2: & \quad \mathbf{3\text{ ATP}} \quad \text{and} \quad \mathbf{2\text{ NADPH}} \end{aligned}

Step 2

Stoichiometry for One Hexose Molecule

Synthesis of one net molecule of glucose ( $C_6H_{12}O_6$ ) requires 6 complete turns of the Calvin cycle fixing 6 $CO_2$ molecules:

\begin{aligned} \text{Total ATP} &= 6 \times 3 = \mathbf{18\text{ ATP}} \\[4pt] \text{Total NADPH}_2 &= 6 \times 2 = \mathbf{12\text{ NADPH}_2} \end{aligned}

Step 3

Overall Balance Sheet

The net input/output equation for glucose synthesis in the dark reaction is:

6CO_2 + 18\text{ATP} + 12\text{NADPH} \longrightarrow C_6H_{12}O_6 + 18\text{ADP} + 18\text{P}_i + 12\text{NADP}^+

⭐

360° Option Elimination Engine Key Feature

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4-Option Deep Scan

1 1

✗ Incorrect

Verdict & Scientific Reason:

NADPH count is overstated; only 12 NADPH are required for reduction of 12 molecules of 3-PGA.

⚠️

Student Fallacy (Why candidates pick this trap): Arbitrarily inflating NADPH counts without balancing the 2 per CO2 reduction step.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Under-counts ATP by omitting the 6 ATP consumed in RuBP regeneration.

⚠️

Student Fallacy (Why candidates pick this trap): Accounting only for the reduction phase (12 ATP) and forgetting RuBP regeneration (6 ATP).

3 3

✓ 100% Correct

Verdict & Scientific Reason:

Exact stoichiometric balance: 18 ATP (12 reduction + 6 regeneration) and 12 NADPH2 (reduction).

💡

Why this is airtight: None; rigorous biochemical stoichiometry.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Both values are incorrect.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing light reaction non-cyclic photophosphorylation ratios with Calvin cycle requirements.

⚠️

NTA Trap Alert: Omitting RuBP Regeneration ATP Trap

Many students only count the 2 ATP used per $CO_2$ during the reduction of 3-PGA to G-3-P (totaling 12 ATP) and completely forget the 1 ATP per $CO_2$ required to regenerate RuBP (totaling 6 ATP).

🛡️ How to avoid the -1 mark: Always remember: 3 ATP per CO2 (2 in reduction + 1 in regeneration). 6 x 3 = 18 ATP!

📖

Core NEET Syllabus Standard

NCERT Biology · Photosynthesis in Higher Plants Standard Benchmark

Core Scientific Principle Tested:

"For every CO2 molecule entering the Calvin cycle, 3 molecules of ATP and 2 of NADPH are required. To make one molecule of glucose, 6 turns of the cycle are required, consuming 18 ATP and 12 NADPH."

Syllabus Focus: The Calvin Cycle

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2023 Botany Question 107 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ 3:2 Ratio Multiplied by 6 Rule

Step-by-Step Rigorous Workflow & Mathematical Proof

Calvin Cycle Phases and Energy Consumption per CO2

Stoichiometry for One Hexose Molecule

Overall Balance Sheet

360° Option Elimination Engine Key Feature

NTA Trap Alert: Omitting RuBP Regeneration ATP Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Photosynthesis in Higher Plants

RuBisCO Oxygenase Catalysis & Identification of 2-Phosphoglycolate

Reaction Centre Chlorophyll a in Photosystem I (P700)

Chronological Sequence of Classic Photosynthesis Experiments

Stoichiometry of the Calvin Cycle (C3 Pathway) per Glucose Formed

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