Question

Sugarcane and corn are one of the most efficient plants in trapping light energy because

• A. They have $C_4$ acid cycle
• B. They do not involve photorespiration
• C. They perform Calvin cycle
• D. All of the above

Answer 1

The correct option is D All of the above

The plants such as sugarcane and maize which are adapted to dry tropical regions have an additional pathway of carbon dioxide fixation known as $C_4$ pathway. These plants can absorb $C{O}_2$ even from a much low $C{O}_2$ concentration when the $C_3$ plants fail to avail. Thus, $C_4$ plants can perform a high rate of photosynthesis even when the stomata are nearly closed. They also maintain a high rate of photosynthesis under conditions of water shortage where the $C_3$ plants would stop photosynthesis. Presence of excess $O_2$ in the surrounding has no inhibitory effect on $C_4$ pathway because the enzyme PEP- carboxylase which is the primary acceptor of $C{O}_2$ is insensitive to $O_2$ whereas in case of $C_3$ plants RUBISCO is sensitive to $O_2$ and starts combining with oxygen instead of $C{O}_2$ and thus starts photorespiration. Photorespiration inhibits the rate of photosynthesis in these plants. On the other hand, photorespiration is absent in $C_4$ plants which are of great advantage to them and helps in conserving water.

Thus, the correct answer is option B.