Question

select the correct answer.
why do plants excrete more carbon dioxide at night than during the day?
a. cellular respiration occurs only at night and not during the day.

b. cellular respiration occurs at a faster rate at night than during the day.

c. photosynthesis uses some of the carbon dioxide released during the day.

d. the light - independent reaction of photosynthesis that releases carbon dioxide occurs at night.

Explanation:

To determine why plants excrete more carbon dioxide at night, we analyze each option:

• Option A: Cellular respiration occurs all the time (day and night), not just at night. Eliminate A.
• Option B: Cellular respiration rate isn't inherently faster at night. During the day, photosynthesis also occurs, but respiration still happens. The key is that at night, photosynthesis (which uses CO₂) stops, so the CO₂ from respiration is not used and is excreted more. But the idea of a faster rate at night is incorrect. Eliminate B.
• Option C: During the day, plants perform photosynthesis which uses CO₂ (including some from respiration). At night, photosynthesis stops, so all the CO₂ produced by cellular respiration is excreted, leading to more CO₂ excretion at night. This makes sense.
• Option D: The light - independent reaction (Calvin cycle) of photosynthesis uses CO₂, and it occurs during the day (as it needs ATP and NADPH from the light - dependent reactions which happen in the day). It does not release CO₂ at night. Eliminate D.

Answer:

C. Photosynthesis uses some of the carbon dioxide released during the day.