Science
Cell transport.
Definition
Cell transport refers to the movement of substances across the cell membrane. Passive transport (diffusion, osmosis, facilitated diffusion) requires no energy, while active transport uses ATP to move molecules against their concentration gradient.
Examples
Real-world.
- 1 Oxygen moves into cells by simple diffusion from high to low concentration
- 2 The sodium-potassium pump actively transports 3 Na⁺ out and 2 K⁺ into the cell using ATP
- 3 Water moves across membranes by osmosis, which is why red blood cells swell in hypotonic solutions
Key Fact
Passive transport moves molecules DOWN the concentration gradient (no ATP); active transport moves them AGAINST it (requires ATP).