A boundary that does work

By Living systems · myAudience

myAudience · AI-generated illustration · Original generated illustration; not documentary evidence

A cell membrane separates the inside from the outside while allowing selected substances to pass. Diffusion follows concentration differences without a direct energy input; other transport processes require energy. “Small” does not automatically mean “passes freely”: chemical properties and membrane proteins matter. Start with the question “what can cross this boundary?” and a cell becomes a working system rather than just a circle in a textbook.