Question

Choose the correct statement(s) about photorespiration:
I. It occurs due to high oxygen concentration and low carbon dioxide condition
II. Warburg effect is a decrease in the rate of photosynthesis at high oxygen content
III. Peroxisome and mitochondria are not related to photorespiration
IV. It involves the oxidation of RuBP

• A. I and III
• B. I and II only
• C. I, II and IV only
• D. III and IV

Answer 1

The correct option is C I, II and IV only

Otto Warburg observed that $O_2$ inhibits photosynthesis in $C_3$ plants. So, the phenomenon of decrease in the rate of photosynthesis at high oxygen content is known as Warburg effect.

RuBisCO is the enzyme that incorporates ${\mathrm{CO}}_2$ into RuBP. But it is a bifunctional enzyme. It has both carboxylase and oxygenase activity.

During carboxylase activity, it will add ${\mathrm{CO}}_2$ to RuBP.

During oxygenase activity, it will oxidise RuBP and form 2-phosphoglycolate and 3-phosphoglycerate. When [${\mathrm{CO}}_2$]: [$O_2$] ratio is high, the enzyme will have carboxylase activity and when it is low the enzyme will have oxygenase activity.

2-phosphoglycolate is metabolized by glycolate cycle and this pathway involves three organelles: chloroplast, peroxisome and mitochondrion.