Final answer:
Cells need to be small to maintain a high surface area to volume ratio, which facilitates efficient material transport and ensures cellular efficiency. Smaller cells can more rapidly acquire nutrients, dispose of waste, and conserve energy, which are essential for cellular function and survival.
Step-by-step explanation:
Cells need to be small in size for a variety of reasons related to their functionality and efficiency. A smaller cell size ensures a larger surface area to volume ratio, which is vital for the efficient transport of materials in and out of the cell. As cells grow, their volume increases much more rapidly than their surface area, leading to a decrease in this ratio. This can limit the cell's ability to obtain nutrients and oxygen, while also impeding the removal of waste products. Furthermore, a higher surface area relative to volume also means a faster exchange of molecules across the cell membrane, so substances have to travel shorter distances within the cell. Both prokaryotic and eukaryotic cells benefit from being small, but eukaryotic cells often have developed additional structural adaptations to facilitate transport due to their relatively larger size. Therefore, being small is critical for cellular efficiency in terms of energy consumption and material transport.