Question

Warburg effect refers to

• 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 1

Answer: (A)

decreased photosynthetic rate at very high $O_{2}$ concentration

Answer 2

Oxygen is a product of photosynthesis, A small quantity of $O_{20}$ is essential for photosynthesis to take place. But as $O_{2}$ concentration rises, rate of photosynthesis decreases, which may be because (i) oxygen takes part in oxidation of photosynthetic pigments, intermediates and enzymes in the presence of strong light (photo-oxidation), (ii) oxygen is a strong 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 photosynthesis begins to decline in all plants. This phenomenon is referred to as Warburg effect.