Final answer:
Cells are small to ensure efficient exchange of materials with the environment. Their size affects the surface area-to-volume ratio, influencing the cell's ability to obtain nutrients and eliminate waste. Cells have developed adaptations to increase their surface area and overcome the limitations of diffusion.
Step-by-step explanation:
Cells are so small because their small size allows for efficient exchange of materials with the environment. The surface area-to-volume ratio of a cell influences how quickly it can obtain nutrients and eliminate waste products. As cells increase in size, their volume increases more rapidly than their surface area, leading to a decrease in the surface area-to-volume ratio.
This decrease in ratio affects the cell's ability to efficiently diffuse substances through its membrane. If a cell becomes too large, its plasma membrane will not have sufficient surface area to support the rate of diffusion required to sustain the increased volume.
To overcome this limitation, cells have developed different adaptations to increase their surface area, such as folding of the cell membrane, elongated shapes, or the presence of organelles that perform specialized functions.