* Diffusion: The movement of molecules from an area of high concentration to an area of low concentration. This movement is driven by the concentration gradient and requires no energy input from the cell. Think of it as things naturally spreading out until they are evenly distributed.
* Active transport: The movement of molecules against their concentration gradient (from an area of low concentration to an area of high concentration). This requires energy, usually in the form of ATP, which is provided by the cell. It's like pushing a ball uphill, requiring effort.
Here are some other key differences:
| Feature | Diffusion | Active transport |
|---|---|---|
| Energy required | No | Yes (from ATP) |
| Movement direction | Down concentration gradient | Against concentration gradient |
| Membrane proteins | Not required | Often required (for binding and transporting) |
| Example | Oxygen moving from the lungs to the bloodstream | Sodium-potassium pump in nerve cells |
In short, diffusion is a passive process driven by the concentration gradient, while active transport is an active process requiring energy to move molecules against the gradient.
