Photosynthesis Practice Test

In a controlled chamber, a plant is kept in constant bright light while CO2 concentration is rapidly decreased. The light reactions continue to generate ATP and NADPH, but the Calvin cycle requires CO2 to incorporate carbon into organic molecules. Which change is most likely in chloroplast metabolite levels shortly after CO2 decreases?

A student measures gas exchange from a photosynthesizing leaf in light. In the thylakoid, water is oxidized, releasing O$_2$ and electrons; electrons move to NADP$^+$, and ATP is produced using a proton gradient. The Calvin cycle in the stroma uses ATP and NADPH to incorporate CO$_2$ into organic molecules. If the leaf is moved to darkness while CO$_2$ remains available, which process is most likely to stop first?