Channel proteins allow specific ions or polar particles to cross membranes by facilitated diffusion, whereas pump proteins use energy from ATP to move specific particles by active transport. Channels move particles down a concentration or electrochemical gradient; pumps can move them against a concentration gradient.
How the mechanisms differ
The phospholipid bilayer’s hydrophobic core has low permeability to ions and many polar molecules. Both protein types provide selective routes across this barrier, but they operate differently.
- A channel protein forms a hydrophilic pore through the membrane. When the channel is open, specific particles move through because of random molecular motion and a gradient; ATP is not directly required. Some channels are gated, opening or closing in response to a signal.
- A pump protein has binding sites for particular particles. ATP supplies energy that changes the protein’s conformation, transferring the particles across the membrane. Because this process is active, pumps can create and maintain concentration gradients.
| Feature | Channel proteins | Pump proteins |
|---|---|---|
| Transport process | Facilitated diffusion | Active transport |
| Direction | Down a concentration or electrochemical gradient | Can move against a concentration gradient |
| Energy | No direct ATP use | Uses energy from ATP |
| Mechanism | Hydrophilic pore permits passage | Binding followed by conformational change |
| Selectivity | Pore structure selects particular ions or particles | Binding site recognizes specific particles |
| Example | Ion channel in a neuron | Sodiumtopotassium pump |
A common misconception is that channels “pull” particles through the membrane. They do not: net movement results from random motion plus an existing gradient. Pumps differ because energy input enables transport that would not occur spontaneously in that direction.
IB exam technique
For an explain question, link structure to mechanism: channel pore → facilitated diffusion down a gradient; pump binding site → ATP-driven conformational change → movement against a gradient. At SL, focus on channel proteins for facilitated diffusion and pump proteins for active transport; the sodiumpotassium pump is an AHL example, so label it as HL-specific.