What happens to the surface area to volume ratio as cell size increases?

• A. It increases as size grows.
• B. It decreases as size increases.
• C. It stays constant regardless of size.
• D. It fluctuates unpredictably.

Answer: (B)

Surface-area-to-volume ratio decreases as cell size increases because surface area grows with length squared while volume grows with length cubed. For a simple cube, SA = 6s^2 and V = s^3, so SA:V = 6/s. Doubling the size halves the ratio, showing it drops as size grows. This matters biologically because the membrane (surface area) is the system that exchanges nutrients and wastes with the environment, and as a cell gets bigger there’s less surface area per unit of volume to support those exchanges. That’s why cells stay small or develop features to increase surface area. So the SA:V ratio goes down with increasing size. It does not increase, stay constant, or fluctuate unpredictably.