Why are small cells favored for exchange with the environment?

• A. To maximize material exchange with the environment; smaller cells have a larger SA:V.
• B. Because they have more mitochondria.
• C. Because they are more evolved.
• D. Because they contain more DNA.

Answer: (A)

The key idea is that material exchange with the environment happens across the cell surface, so how much membrane area there is relative to the cell’s interior matters. Smaller cells have a higher surface area to volume ratio, meaning more membrane surface for substances to pass through per unit of cytoplasm. This allows nutrients and oxygen to enter, wastes to exit, and diffusion to occur more quickly because the maximum distance any molecule has to travel inside the cell is shorter. In short, the increased SA:V in small cells makes exchange with the environment faster and more efficient. Features like having more mitochondria or containing more DNA don’t directly affect this exchange rate, and being more evolved isn’t the reason for the preference.