Question

1. when the light - independent reactions are occurring, gases diffuse between the chloroplast and the air that surrounds the plant. why is gas diffusion essential during this stage of photosynthesis?

a. water vapor is used to assemble sugar molecules.
b. carbon dioxide is used to assemble sugar molecules.
c. molecular oxygen is used to assemble sugar molecules.
d. water vapor is released as a waste product.

Explanation:

In the light - independent reactions (Calvin cycle) of photosynthesis in the chloroplast, carbon dioxide is used to assemble sugar molecules. Water vapor is related to transpiration and not directly to sugar - molecule assembly in the Calvin cycle. Molecular oxygen is a product of the light - dependent reactions, not used to assemble sugar molecules. Gas diffusion is essential because carbon dioxide is needed for the synthesis of sugar in the light - independent reactions.

Answer:

b. Carbon dioxide is used to assemble sugar molecules.