Here's why:

* Structure determines function: Just like a hammer is designed for pounding nails, a cell's shape, components, and organization are specifically suited for its particular role.

* Specialized structures: Different cells have different structures to carry out different functions. For example, muscle cells have long, thin fibers for contraction, nerve cells have long axons for transmitting signals, and red blood cells have a flattened, disk-like shape to carry oxygen.

* Organelles: Within a cell, specific organelles (like the nucleus, mitochondria, and Golgi apparatus) perform specific tasks. These organelles are structurally adapted to their functions.

While the environment and interactions with other cells also play a role, the fundamental basis of a cell's function is its structure.