NEET 2024 — Biology solution

NEET2024Biology

Given below are two statements:

Statement I: In C $_{3}$ plants, some O $_{2}$ binds to RuBisCO, hence CO $_{2}$ fixation is decreased.
Statement II: In C $_{4}$ 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:

A
Statement I is true but Statement II is false
B
Statement I is false but Statement II is true
C
Both Statement I and Statement II are true
D
Both Statement I and Statement II are false

Solution

In C $_{3}$ plants RuBisCO can bind O $_{2}$ instead of CO $_{2}$ (it has dual carboxylase / oxygenase activity), reducing CO $_{2}$ fixation — Statement I is correct. In C $_{4}$ plants, primary CO $_{2}$ fixation occurs in mesophyll cells by PEP carboxylase (which has no oxygenase activity), and the Calvin cycle (with RuBisCO) is confined to bundle sheath cells where CO $_{2}$ is concentrated; so photorespiration is essentially absent in both cell types of C $_{4}$ plants, not just bundle sheath. Statement II is therefore incorrect as worded.

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