What effect would occur on photosynthesis, if the amount of oxygen in the atmospheric decreases

Options

A. Increase in the `C_3` cycle and a decrease in the `C_4` cycle
B. Increase in the `C_4` cycle and a decrease in the `C_3` cycle
C. Increase in the `C_3` cycle and no change in `C_4` cycle
D. Increase in the `C_4` cycle and no change in `C_3` cycle

Answer

C

Explanation

Oxygen has been shown to inhibit photosynthesis in `C_3` a plant that exhibits photosynthesis because:
* It favours rapid respiration which utilizes common intermediates.
* It competes with `CO_2`.
* It destroys the excited state of chlorophyll.