Question

In comparison to the $C_3$ plant, which of the following is true for ${\mathrm{CO}}_2$ compensation point of $C_4$?

• A. $C_4$ plants will have a lower ${\mathrm{CO}}_2$ compensation point
• B. $C_4$ plants will have a higher ${\mathrm{CO}}_2$ compensation point
• C. $C_4$ plants require higher ${\mathrm{CO}}_2$ concentration to reach the compensation point
• D. $C_3$ plants require lower ${\mathrm{CO}}_2$ concentration to reach the compensation point

Answer 1

The correct option is A $C_4$ plants will have a lower ${\mathrm{CO}}_2$ compensation point

${\mathrm{CO}}_2$ compensation point is the concentration of ${\mathrm{CO}}_2$ at which the amount of ${\mathrm{CO}}_2$ consumed during photosynthesis is equal to the concentration of ${\mathrm{CO}}_2$ released during the various processes of respiration.

In case of $C_3$ plants, ${\mathrm{CO}}_2$ is produced by photorespiration and cellular respiration.

Whereas in case of a $C_4$ plant, photorespiration doesn't occur due to ${\mathrm{CO}}_2$ concentrating mechanisms and ${\mathrm{CO}}_2$ is produced only by cellular respiration.

Hence, in $C_3$ plants, higher ${\mathrm{CO}}_2$ concentration is needed for carboxylase activity of $\mathrm{RuBisCO}$ and to prevent photorespiration.

Whereas $C_4$ plants can carry out photosynthesis at even low ${\mathrm{CO}}_2$: $O_2$ concentration ratios.

Hence, $C_4$ plants will require a lower ${\mathrm{CO}}_2$ concentration for photosynthesis and, in turn, will have a lower compensation point.