8. You measure the photorespiration rate of a C3 plant and a C4 plant under the

Question

8. You measure the photorespiration rate of a C3 plant and a C4 plant under the current atmospheric O2 concentration (20%). You then increase the atmospheric concentration of O2 to 30%. How will the photorespiration rates of the C3 and C4 plants be affected by this change?

A. The photorespiration rates will increase greatly in both the C3 and C4 plants

B. The photorespiration rate will increase greatly in the C3 plant but only slightly in the C4 plant

C. The photorespiration rate will increase greatly in the C4 plant but only slightly in the C3 plant D. The photorespiration rates will increase only slightly in both the C3 and C4 plants

PLEASE EXPLAIN WHY!!

Explanation / Answer

How will the photorespiration rates of the C3 and C4 plants be affected by this change?

B) The photorespiration rate will increase greatly in the C3 plant but only slightly in the C4 plant

Increased oxygen concentration results a proportional decrease in the rates of true and of apparent photosynthesis, and proportional increases in the CO2 evolution (true photosynthesis minus apparent photosynthesis) in C3 plants. The inhibition of apparent photosynthesis is not entirely attributable to the increased photorespiration but was roughly equally divided between an inhibition of true photosynthesis and a stimulation of CO2 evolution in the light. On the other hand, in C4 plants, there is no effect/slight effect of oxygen concentration on both the rates of true and apparent photosynthesis, and there is no large CO2 evolution occurred in C4 plants.

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