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Question #45981

Difficulty: 8/10 | 🟢 Free

The Question

A $C_4$ plant is cultivated under artificially elevated $CO_2$ concentration and low irradiance. Upon exposure to its critical photoperiod, florigen is synthesized in the leaves and translocated to the shoot apex to induce flowering. Which of the following best describes the metabolic reality for this plant during its reproductive transition?

Options

A.
It faces a severe energetic deficit because the 30 ATP requirement of the $C_4$ pathway acts as a metabolic tax, offering no carbon fixation advantage over $C_3$ plants in high $CO_2$ .
B.
It exhibits a pronounced $CO_2$ fertilization effect, which compensates for the low irradiance and provides abundant assimilates for floral primordia development.
C.
It temporarily suspends the activity of PEP carboxylase in the mesophyll cells, reverting to a $C_3$ -like carbon fixation to conserve ATP for reproduction.
D.
The high $CO_2$ concentration suppresses RuBisCO's oxygenase activity in the bundle sheath, generating a surplus of ATP that accelerates the transition to flowering.

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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

Photoperiodism Thresholds|Kranz Anatomy Adaptations|Phytochrome

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students often memorize that ' $C_4$ plants are more efficient than $C_3$ plants' without understanding the environmental context.

The trap relies on failing to recognize that the $C_4$ pathway is an evolutionary adaptation to low $CO_2$ /high temperature, and its extra ATP cost becomes a severe disadvantage (a metabolic tax) under high $CO_2$ and low light, especially when energy is diverted to flowering.

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Plant Growth and Development - Class 11
Concept	Photoperiodism Thresholds
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free