3. During photorespiration which organelle is involved in conversion of glycolate into glyoxylate?
(1) Mitochondria     (2) Peroxisomes
(3) Chloroplast       (4) Nucleus

The correct answer is (2) Peroxisomes.

Detailed Explanation

During photorespiration in C3 plants, glycolate produced in the chloroplasts is transported to peroxisomes. In peroxisomes, glycolate is oxidized to glyoxylate by the enzyme glycolate oxidase. This reaction consumes oxygen and releases hydrogen peroxide (H₂O₂), which is then rapidly broken down by catalase in the same organelle to prevent oxidative damage.

Breakdown of Other Options:

• (1) Mitochondria: Mitochondria are involved later in the photorespiratory pathway, specifically in converting glycine to serine, but they do not convert glycolate to glyoxylate.

• (3) Chloroplast: Chloroplasts produce glycolate, but the oxidation of glycolate to glyoxylate does not occur here.

• (4) Nucleus: The nucleus is the control center of the cell but does not participate in photorespiratory metabolism.

Why Peroxisomes?

Peroxisomes contain the key enzyme glycolate oxidase along with catalase, making them the site for the crucial conversion of glycolate into glyoxylate during photorespiration.