Which statement describes leaf anatomy differences that contribute to water-use efficiency in C4 plants?

• A. C4 plants have Kranz anatomy with bundle-sheath cells, enabling efficient carbon fixation.
• B. C3 plants have Kranz anatomy.
• C. C4 plants use mesophyll photosynthesis.
• D. There is no difference between C3 and C4.

Answer: (A)

Kranz anatomy with bundle-sheath cells is the feature that boosts water-use efficiency in C4 plants. In this arrangement, mesophyll cells fix CO2 into a four-carbon compound using the enzyme PEP carboxylase, then this compound is transported to surrounding bundle-sheath cells where CO2 is released for the Calvin cycle in the presence of Rubisco. This spatial separation concentrates CO2 around Rubisco, dramatically reducing photorespiration and allowing the plant to keep stomata partly closed under hot, dry conditions. That means more carbon fixed per unit water lost, i.e., higher water-use efficiency, especially in arid environments. The other statements aren’t correct: C3 plants don’t have Kranz anatomy; C4 plants still use mesophyll cells for initial CO2 fixation but the Calvin cycle occurs mainly in bundle-sheath cells; and there is a real difference in leaf anatomy between C3 and C4.