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Question #47615

Difficulty: 8/10 | 🟢 Free

The Question

To synthesize one molecule of glucose, a $C_4$ plant requires a higher total expenditure of ATP compared to a $C_3$ plant. Which of the following options correctly identifies the exact number of additional ATP molecules required per glucose, the specific cellular location and biochemical step where this extra energy is consumed, and the environmental condition where this metabolic trade-off becomes a distinct disadvantage for the $C_4$ plant?

Options

A.
12 ATP; Mesophyll cells during the regeneration of phosphoenolpyruvate (PEP) from pyruvate; Cool climates with high atmospheric $CO_2$ .
B.
12 ATP; Bundle sheath cells during the decarboxylation of malic acid to release $CO_2$ ; Hot and dry climates with low atmospheric $CO_2$ .
C.
2 ATP; Mesophyll cells during the primary fixation of $CO_2$ into oxaloacetic acid (OAA); Cool climates with high atmospheric $CO_2$ .
D.
18 ATP; Bundle sheath cells during the regeneration of RuBP in the Calvin cycle; Hot and dry climates with low atmospheric $CO_2$ .

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Comparative_Analysis

Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.

Concepts Behind This Question

PEP_Carboxylase|Kranz_Anatomy|RuBisCO

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students often memorize the blanket statement that ' $C_4$ plants are more efficient' without understanding the conditional nature of this efficiency.

The trap relies on quantitative nuance (failing to multiply the 2 ATP cost per $CO_2$ by 6 to get the per-glucose cost) and location specificity (confusing mesophyll PEP regeneration with bundle sheath Calvin cycle events).

It tests the deep NCERT concept that $C_4$ photosynthesis is an evolutionary trade-off, not an absolute superiority.

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Photosynthesis in Higher Plants - Class 11
Concept	Photorespiration Metabolic Cost
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free