Structure Determines Function

Biology is built on a simple but powerful idea: the shape and arrangement of a structure are matched to the job it performs. From the folded membranes of a mitochondrion to the branching airways of a lung, form and function fit together like a key and a lock. Understanding this relationship lets you predict how an unfamiliar structure works and explains why organisms of very different sizes solve the same problems in different ways.

Form and Function Across Scales

The form–function relationship appears at every level of biological organization. At the molecular level, an enzyme's active site has a shape complementary to its substrate, so only the correct molecule binds and reacts. At the cellular level, a red blood cell's biconcave disc shape increases the surface area available for gas ex