Plants have evolved different pathways to capture carbon dioxide during photosynthesis, most notably the C3 and C4 pathways. While both systems utilize the enzyme Rubisco to ultimately produce sugars, they differ fundamentally in their initial carbon fixation steps and internal anatomy. C3 plants, which include wheat and rice, fix carbon into a three-carbon compound directly within their mesophyll cells. In contrast, C4 plants, such as corn and sugarcane, first fix carbon into a four-carbon compound in the mesophyll cells before transporting it to specialized bundle sheath cells where Rubisco is concentrated. This physical separation allows C4 plants to minimize photorespiration, a wasteful process that frequently occurs in C3 plants under high-light and high-temperature conditions. Consequently, C4 plants exhibit a much higher water-use efficiency in hot, arid environments compared to C3 plants, though C3 plants remain more energy-efficient in cooler, temperate climates.
Based on the passage, which of the following is an explicit difference in the carbon fixation processes of C3 and C4 plants?
- C3 plants fix carbon into a three-carbon compound directly within mesophyll cells, whereas C4 plants transport a four-carbon compound from mesophyll cells to bundle sheath cells.Answer
- BC3 plants concentrate the enzyme Rubisco inside specialized bundle sheath cells, whereas C4 plants keep Rubisco distributed throughout all leaf tissues.
- CC4 plants transport carbon directly to the bundle sheath cells before performing any initial carbon fixation in the mesophyll cells.
- DC3 plants perform carbon fixation in cooler climates without using Rubisco, whereas C4 plants rely on Rubisco exclusively in hot, arid environments.