Question

Photorespiration is a prominent feature of plants having

• A. $C_3$ cycle
• B. $C_4$ cycle
• C. aerobic respiration
• D. none of these

Answer 1

Answer: (A)

$C_3$ cycle

Answer 2

Photorespiration refers to oxidation of glycolate. It is produced during glycolate metabolism of photosynthesis and occurs in three organelles peroxisomes, mitochondria and chloroplast. Hence possible only in green parts of plant. Photorespiration occurs only in $C_3$ plants because at high temperature and high oxygen concentration $RuBP$ carboxylase is changed to $RuBP$ oxygenase. Photorespiration is absent in $C_4$ plants because Rubisco and other Calvin cycle enzymes are present only in bundle sheath cells, and $CO_2$ concentration in those cells is maintained too high for $O_2$ to compete with $CO_2$. Temperature is also low in bundle sheath cells of $C_4$ plant.