Photosynthesis Determinants of Photosynthetic Rate 5

Question 1

CAM plants open their stomata at night to fix CO₂. How does this adaptation affect their photosynthetic rate during the day?

Accepted Answer

Daytime photosynthetic rate is limited by CO₂ derived from nightly storage, making overall rates lower than C3 plants

Answer

CAM plants rely on malic acid stored overnight as their daytime CO₂ source; this supply is finite and lower than open-stomata CO₂ flux, resulting in generally lower overall photosynthetic rates.

Question 2

How does soil waterlogging reduce photosynthetic rate even when water is abundant?

Accepted Answer

Anaerobic root conditions impair nutrient uptake and root function, reducing ion supply needed for photosynthesis

Answer

Waterlogged soils become anaerobic, impairing root respiration and active ion transport, so mineral nutrients like magnesium and nitrogen are less available for chlorophyll and enzyme synthesis.

Question 3

What is the Blackman limiting factor principle as applied to photosynthesis?

Accepted Answer

At any given moment, the rate of photosynthesis is limited by the single factor in shortest supply

Answer

Blackman's law of limiting factors states that when a process depends on multiple factors, the rate is controlled by whichever factor is most limiting at that moment.

Question 4

A C3 crop plant shows higher photosynthetic rates in the morning and late afternoon but lower rates at midday on a hot summer day. What best explains the midday depression?

Accepted Answer

Midday heat causes stomatal closure to conserve water, reducing CO₂ entry

Answer

High midday temperatures and vapor pressure deficits trigger stomatal closure, restricting CO₂ diffusion into the leaf and causing the characteristic midday photosynthetic depression.

Question 5

Which statement about the effect of CO₂ concentration on C4 plants versus C3 plants is correct?

Accepted Answer

C3 plants generally show a greater response to elevated CO₂ because they do not concentrate CO₂ and are more often CO₂-limited

Answer

C4 plants already saturate RuBisCO with CO₂ via their concentrating mechanism, so additional atmospheric CO₂ provides little benefit; C3 plants, lacking this mechanism, gain more from elevated CO₂.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Determinants of Photosynthetic Rate 5