Which of the following is an advantage of the C4 pathway over the C3 pathway in plants?

• A. C4 plants are more efficient at fixing carbon dioxide in cool, moist environments.
• B. C4 plants require less ATP per molecule of glucose produced than C3 plants.
• C. C4 plants do not use the enzyme RuBisCO for carbon fixation.
• D. C4 plants have higher photosynthetic efficiency under high light intensity and temperature.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the difference between the C3 and C4 pathways. The C3 pathway is the most common form of photosynthesis, where carbon dioxide is fixed directly by the enzyme RuBisCO into a 3-carbon compound (3-phosphoglycerate). The C4 pathway, on the other hand, involves an additional step where carbon dioxide is first fixed into a 4-carbon compound (oxaloacetate) by the enzyme PEP carboxylase before being transferred to RuBisCO.
2. Step 2: Recognize the environmental conditions that favor each pathway. C3 plants are more efficient in cool, moist environments with moderate light intensity, while C4 plants are adapted to high light intensity, high temperatures, and dry conditions. This adaptation allows C4 plants to minimize photorespiration, which is a wasteful process that occurs in C3 plants under these conditions.
3. Step 3: Analyze the role of RuBisCO in both pathways. RuBisCO is used in both C3 and C4 plants for carbon fixation during the Calvin cycle. However, C4 plants use PEP carboxylase in the initial step of carbon fixation, which has a higher affinity for carbon dioxide and is not affected by oxygen levels, reducing photorespiration.
4. Step 4: Evaluate the energy requirements of the C4 pathway. While the C4 pathway requires more ATP than the C3 pathway due to the additional steps involved, this energy cost is offset by the higher photosynthetic efficiency under high light intensity and temperature conditions.
5. Step 5: Conclude that the advantage of the C4 pathway over the C3 pathway is its higher photosynthetic efficiency under high light intensity and temperature, making it better suited for plants in hot and dry environments.