Assertion : $C_4$ photosynthetic pathway is more efficient than the $\mathrm{C}_3$ pathway. Reason :…
Assertion : $C_4$ photosynthetic pathway is more efficient than the $\mathrm{C}_3$ pathway.
Reason : Photorespiration is suppressed in $\mathrm{C}_4$ plants.
If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion
If assertion is true but reason is false
If both assertion and reason are false.
Solution
$\mathrm{C}_4$ photosynthetic pathway is more efficient than $\mathrm{C}_3$ pathway as $\mathrm{C}_4$ plants can pick up $\mathrm{CO}_2$ even when it is found in low concentration. PEP enzymes shows high affinity for $\mathrm{CO}_2 . \mathrm{C}_4$ plants contain two types of chloroplast (Kranz anatomy) : bundle sheath chloroplast and mesophyll chloroplast. Bundle sheath cells contain Calvin cycle enzymes. Due to high concentration of $\mathrm{CO}_2$ in bundle sheath cells, RuBP carboxylase works only for Calvin cycle and not for photorespiration.
Photorespiration is a wasteful process as it works to undo the act of photosynthesis in $\mathrm{C}_3$ plants. No energy rich compound is produced in this process. When temperature increase more and more photosynthetically fixed carbon is lost by photorespiration thus reducing the efficiency of $C_3$ plants.