Multiple choice

Which one of the following is the correct sequence of the appearance of intermediate compounds in the pathway of photorespiration ?

  1. Glyoxylate - glycine - glycolate - serine

  2. Glyoxylate - serine - glycolate - glycine

  3. Glycolate - glyoxylate - glycine - serine

  4. Glycolate - glyoxylate - serine - glycine

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C Correct answer
Explanation

Photorespiration begins when RuBP oxygenase produces phosphoglycolate, which is converted to glycolate. Glycolate exits chloroplasts, enters peroxisomes, and is converted to glyoxylate. Glyoxylate then transaminates to glycine. Glycine enters mitochondria, where two molecules combine to form serine, releasing CO2 and NH3. Thus the sequence is: Glycolate → glyoxylate → glycine → serine.