VCE Biology Unit 1 AOS 1 Practice Test 2026 – Complete Exam Prep

The key idea is that diffusion relies on how much membrane surface is available compared with the cell’s interior volume. A flattened cell has more surface area relative to its volume than a rounded, compact one, so there’s more membrane for transport without needing a large increase in interior space. This higher surface area to volume allows faster exchange of nutrients, gases, and wastes with the environment. In contrast, a spherical shape minimizes surface area for a given volume, reducing the rate at which exchanges can occur. A rigid cell wall or a uniform cytoplasm doesn’t inherently change the geometry of the cell surface, so they don’t increase the surface area to volume ratio. Thus, the feature that increases the surface area to volume ratio is a flattened shape.