Why are plants unlikely to produce many carbohydrates at night?
A)Selected Calvin cycle enzymes are inactive in the dark because they are hydrogen-bound at night.
B)Calvin cycle enzymes are denatured in the cold temperatures at night.
C)Selected Calvin cycle enzymes are inactive in the dark because thioredoxin is oxidized and cannot reduce their disulfide linkages.
D)Selected Calvin cycle enzymes are inactive in the dark because thioredoxin is reduced and can break their disulfide linkages.

Question

Quizplus · Accepted Answer

Selected Calvin cycle enzymes require reduced thioredoxin to reduce their disulfide linkages and become active. However, thioredoxin is oxidized at night because there is no light energy to drive electron transport and generate reducing power. Therefore, these enzymes remain inactive and plants are unlikely to produce many carbohydrates at night.

Why Are Plants Unlikely to Produce Many Carbohydrates at Night