4. Which one of the following metabolites moves from rnitochondria to peroxisome during the operation of the C2 oxidative photosynthetic cycle?
(1) Glycerate (2) Glycolate
(3) Glycine    (4) Serine

Introduction

The C2 oxidative photosynthetic cycle, also known as photorespiration, involves a complex metabolite shuttle between chloroplasts, mitochondria, and peroxisomes. Identifying which metabolites move between these organelles is key to understanding photorespiratory metabolism in plants.

Explanation of Each Option

(1) Glycerate

• Glycerate is produced in peroxisomes and transported to chloroplasts, not mitochondria to peroxisomes.

(2) Glycolate

• Glycolate is formed in chloroplasts and transported to peroxisomes, not from mitochondria.

(3) Glycine

• Correct. Glycine is formed in peroxisomes during photorespiration and transported to mitochondria where it is converted to serine. The two-carbon atom glycine then moves back from mitochondria to peroxisomes as part of this cycle.

(4) Serine

• Serine is produced in mitochondria from glycine but is transported to the peroxisome after glycine conversion; still, the primary metabolite moving from mitochondria to peroxisomes is glycine.

Why Glycine Is Correct

During photorespiration, glycine is the principal metabolite transported from mitochondria to peroxisomes. This transport is vital for the continuation of the cycle that recovers carbon from glycolate metabolism and protects against photorespiratory damage.

Understanding inter-organelle metabolite transport in the C2 cycle is fundamental for plant physiology, especially in photosynthesis and photorespiration research contexts.