From cells to organisms

Cooperation at scale.

Specialisation

Cells differentiate into muscle, nerve, blood and skin, each doing one job well and depending on the others. Multicellular life is a bargain: give up independence, gain capability.

Stem cells retain the ability to become several types.
Cancer is that bargain breaking down: cells that stop cooperating.

Homeostasis

Organisms hold internal conditions steady against a changing outside: temperature, acidity, water, sugar. Most physiology is a control loop doing exactly that.