Cold slows respiratory enzyme activity, reducing body heat production

Steps:

• Exposure to 3°C air causes rapid heat loss from the body to the environment.
• To compensate, metabolic rate should increase, but cold inhibits this process.
• Respiration, a key heat-generating metabolic pathway, relies on enzymes.
• Lower temperatures reduce enzyme efficiency, slowing respiration and heat output, leading to body temperature drop.

Why D is correct:

• Enzymes in respiration have an optimal temperature around 37°C; below this, reaction rates slow per the Q10 temperature coefficient, where activity roughly halves for every 10°C drop, reducing ATP and heat production.

Why the others are wrong:

• A: Carbon dioxide removal occurs via diffusion in lungs, unaffected by external cold.
• B: Glucose availability does not limit respiration in this scenario; cold directly impacts enzyme kinetics.
• C: Cold air has the same oxygen percentage (21%) as warm air, just higher density, so oxygen intake remains adequate.

Final answer: D