Lipids, which are fats and oils, make up the membranes of cells and intracellular compartments called organelles. Membranes are a crucial ingredient in cells because they create an oily phase that doesn’t mix with water thereby providing the basis for concentrating specific kinds of molecules in specific compartments. As we’ve discussed, concentrating a molecule is a way of forming a non-equilibrium material distribution which can perform organized work as that concentration gradient spontaneously dissipates toward its equilibrium value. So lipids are responsible for creating the boundary conditions necessary for cellular organization.
Here’s a cartoon of a protein in a membrane doing work to equilibrate a concentration gradient that exists because hydrophilic and/or charged particles can’t pass through the oily membrane:
