Question

$C_4$ plants are more efficient in photosynthesis than $C_3$ plants due to

• A. Lower rate of photorespiration.
• B. Higher leaf area.
• C. Presence of larger number of chloroplasts in the leaf cells.
• D. Presence of thin cuticle.

Answer 1

The correct option is A Lower rate of photorespiration.

In $C_3$ plants, $C{O}_2$ is pumped directly into the Calvin cycle, leaving rubisco exposed to $O_2$. Rubisco in a $C_3$ will take up $O_2$ rather than $C{O}_2$ to undergo photorespiration. Photorespiration occurs under low concentrations of $C{O}_2$ and high concentrations of $O_2$. This process reduces efficiency of photosynthesis, potentially reducing photosynthetic output by 25% in $C_3$ plants. $C_4$ plants capture carbon dioxide in their mesophyll cells forming oxaloacetate. This oxaloacetate is then converted to malate and is transported into the bundle sheath cells, where oxygen concentration is low to avoid photorespiration. So, $C_4$ plants are more efficient in photosynthesis than $C_3$ plants. Thus, option A is correct.