47. The evolutionary adaptation of C4 photosynthesis minimizes the photorespiratory deficit by ensuring a high local concentration of CO₂ near the enzyme rubisco. This mechanism relies on the spatial segregation of tasks, primarily in the bundle-sheath cells, whose chloroplasts are specialized to contain Photosystem I (PS I) but often lack functional Photosystem II (PS II). How does the absence of Photosystem II (PS II) in the bundle-sheath chloroplasts contribute to minimizing photorespiration, even though the cell is operating under conditions of intense light?
(A) The resulting reliance on cyclic electron flow generates the low ratio of ATP to NADPH required to drive the reduction of CO₂ and outcompete the photorespiration pathway.
(B) The four-carbon compound (e.g., malate) delivered from the mesophyll cells is designed to directly activate PS I, allowing it to generate the necessary high-energy electrons without relying on water.
(C) The inhibition of H₂O splitting, which normally occurs at PS II, prevents the release of O₂ gas directly into the local environment where the Calvin cycle and rubisco are confined.
(D) The PS I-only system utilizes an alternate terminal electron acceptor, which binds to O₂ and converts it into water, thus chemically removing the substrate for photorespiration.
(E) The bundle sheath cells primarily serve to regenerate the enzyme PEP carboxylase, a process that is independent of O₂ concentration and requires only the minimal ATP produced by cyclic flow.