Warbung effect refers to

Options

A. decreased photosynthetic rate at very high `O_(2)` concentration
B. increased photosynthetic rate at very high `O_(2)` concentration
C. decreased photosynthetic rate at very low `O_(2)` concentration
D. increased photosynthetic rate at very low `O_(2)` concentration

Answer

A

Explanation

Oxygen is a product of photosynthesis. A small quantity of `O_(2)` is essential for photosynthesis to take place. But as `O_(2)` concentration rises, rate of photosynthesis decreases, which may be because (i) oxygen takes takes part in oxidation of photosynthetic pigments, intermediates and enzymes in the presence of strong light (photo-oxidation), (ii) oxygen is a storng quencher of excited state of chlorophyll. Oxygen competes with `CO_(2)` for reducing power. It converts RuBP-carboxylase to RuBP-oxygenase. At very high oxygen concentration, the rate of photsynthesis begins to decline in all plants. This pehnomenon is referred tp as Warnirg effect/