NEET (UG) 2024 — Question 136

RuBisCO catalyses both carboxylation and oxygenation; $\ce{CO2}$ and $\ce{O2}$ compete for the same active site. In $C_3$ plants, when $\ce{O2}$ binds RuBisCO, photorespiration occurs and $\ce{CO2}$ fixation decreases. Hence Statement I is true. In $C_4$ plants, mesophyll cells contain PEP carboxylase but no RuBisCO, so they show no photorespiration. Bundle sheath cells contain RuBisCO, but the high $\ce{CO2}$ concentration there suppresses the oxygenase activity. Thus photorespiration is essentially absent in $C_4$ plants; mesophyll cells do not show 'very little' photorespiration, they show none. Consequently, Statement II is false as worded. Therefore, Statement I is true and Statement II is false, so the correct answer is C.