3a. How would an O2 evolution curve appear if the stomata of a leaf closed during an experiment?

We would expect a pattern similar to that shown in curve C. The rate of O2 evolution will slow as photosynthesis ceases, due to lack of CO2. When the rate of the light-independent reaction slows due to a lack of CO2, the overall rate of photosynthesis and O2 evolution will begin to slow.

Note that curve D is incorrect because we would not necessarily expect the the amount of O2 in the leaf chamber to drop rapidly when photosynthesis stops; rather, as photosynthesis ceases, the O2 concentration will level off.

 

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