Given below are two statements. Statement 1: in C3 plants, some O2 binds to RuBisCO, hence CO2 fixation is decreased. Statement 2: In C4 plants, mesophyll cells show very little photorespiration while bundle sheath cells do not show photorespiration. In the light of the above statements, choose the correct answer from the options given below.
Answer: (B) Statement I is true but Statement II is false. Statement 1 is true: in C3 plants O2 competes with CO2 for RuBisCO's active site, so when O2 binds, CO2 fixation is decreased (photorespiration).
- A.Both Statement I and Statement II are false
- B.Statement I is true but Statement II is false✓
- C.Statement I is false but Statement II is true
- D.Both Statement I and Statement II are true
Correct Answer
(B) Statement I is true but Statement II is false
Solution & Explanation
Statement 1 is true: in C3 plants O2 competes with CO2 for RuBisCO's active site, so when O2 binds, CO2 fixation is decreased (photorespiration). Statement 2 is false: in C4 plants photorespiration does not occur at all, because the bundle sheath mechanism concentrates CO2 so RuBisCO acts as a carboxylase; the statement's split of 'little' vs 'no' photorespiration between mesophyll and bundle sheath is incorrect. Hence Statement I is true but Statement II is false. NCERT: Class 11 Ch 11, p.147 [147:037]: "In C3 plants some O2 does bind to RuBisCO, and hence CO2 fixation is"