7. Why doesn't the light response curve pass through the origin?


Processes occur in leaves that cause an uptake of O2 from the air. One of these processes is cellular respiration. (What other process related to photosynthesis also utilizes O2?) Under 'normal' light conditions, the rate of photosynthesis greatly exceeds that of O2 uptake processes, and we see a net release of O2. However, under very low light conditions, the amount of O2 being taken up exceeds that produced by photosynthesis, and we see no net O2 evolution-- even a slight net uptake.

7a. The photosynthetic light response curve can also be used to determine the rate of O2 uptake that is occurring in the leaf. Which value obtained from a light response curve could be used as a measure of O2 uptake in the leaf? (select answer by clicking on name of value)

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