Question

What is the reason for $C_4$ grasses doing better than $C_3$ grasses in hot dry environments?

• A. $C_4$ grasses keep thye stomata open at night.
• B. $C_4$ grasses have nearly eliminated photorespiration.
• C. $C_4$ grasses generate a positive turgor pressure under high temperatures.
• D. Cellular respiration rate is higher for a $C_3$ grass than for a $C_4$ grass at higher temperatures.

Answer 1

Answer: (B)

The C4 pathway is also known as the Hatch and Slack pathway, occurs in the plant that is adapted to dry tropical regions, e.g., Sugarcane, Maize, grasses etc. These plants lack a wasteful process called photorespiration and therefore, this shows greater productivity and higher yield as compared to the C3 plants. It is a cyclic process in which the primary CO₂ acceptor is three-carbon molecule phosphoenolpyruvate which is present in mesophylls cells. PEP carboxylase or PEPcase is the enzyme that catalyzes the CO₂ fixation. In the C4 plants, the mesophyll cells lack the enzyme RuBisCO. The 4-Carbon oxaloacetic acid is formed in the mesophyll cell, which is the first product of this pathway. In the mesophyll cells, the oxaloacetic acid is then converted to other 4-carbon compounds like malic acid or aspartic acid and then it is transported to the bundle sheath cells. To release CO₂ and a 3-carbon molecule in the bundle sheath cells, these C4 acids are broken down and the CO₂ released in the bundle sheath cells enter the Calvin pathway.