How does the structure of bundle-sheath cells in C4 plants differ from that in C3 plants?

The structure of bundle-sheath cells in C4 plants is specifically adapted for the process of photosynthesis, particularly in the way these plants utilize carbon dioxide. In C4 plants, bundle-sheath cells are tightly packed around the vascular tissue and play a crucial role in the C4 pathway of carbon fixation. This adaptation allows C4 plants to efficiently concentrate carbon dioxide and minimize water loss, making them well-suited for hot and dry environments.

These cells contain high levels of the enzyme RuBisCO and are involved in the conversion of the 4-carbon compound, oxaloacetate, into malate, which is then transported into the bundle-sheath cells where photosynthesis occurs. This structural specialization enhances the efficiency of carbon fixation compared to C3 plants, where bundle-sheath cells do not play a significant role in fixing carbon dioxide.

In contrast, other options do not accurately describe the unique features of bundle-sheath cells in C4 plants. For instance, they are not necessarily larger and more abundant than in C3 plants, nor do they serve no function in photosynthesis. Additionally, while they provide some protection, their primary role is related to carbon fixation rather than just functioning as a protective layer.