Membrane Transport
Introduced| English |
|---|
| passive transport/ˈpæsɪv ˈtrænspɔːt/ |
| active transport/ˈæktɪv ˈtrænspɔːt/ |
Two ways across the membrane
- A cell must move materials in and out all day long.
- Some movement is free; some has to be paid for with energy.
- The direction of travel decides which one is needed.
- Sorting transport into these two kinds makes it all click.
Passive transport: free
- Passive transport 被动运输 moves substances down their concentration gradient.
- It uses no energy — the particles' own motion does the work.
- Simple diffusion, facilitated diffusion, and osmosis are all passive.
- Movement continues until the gradient disappears.
Passive transport moves substances…
Passive transport goes down the concentration gradient and costs the cell no energy.
Active transport: pay with ATP
- Active transport 主动运输 moves substances against their gradient — from low to high.
- Going uphill needs energy, supplied by ATP.
- A carrier protein acts as a pump, using that energy.
- This lets a cell build up a substance far above its surroundings.
What makes active transport different from passive transport?
Active transport spends ATP to pump substances against their gradient, from low to high.
Active transport requires energy from ATP.
Moving substances uphill against a gradient needs energy — supplied by ATP.
Comparing the two
- Passive goes with the gradient; active goes against it.
- Passive is free; active costs ATP.
- Both can use proteins, but only active spends energy.
- The direction of travel is the quickest way to tell them apart.
Passive or active?
Sort each kind of transport by whether it needs energy and which way it moves.
The passive movement of water across a membrane has a special name: ____.
Osmosis is the passive diffusion of water across a selectively permeable membrane.
Select all true statements about membrane transport.
Passive transport needs no energy, so not all transport does. The other three are correct.
The tell-tale is direction, not speed. If a substance is moving against its gradient (low to high), it must be active transport using ATP — nothing moves uphill for free. Down the gradient is passive.
Root cells pumping in minerals:
- Soil often has a lower mineral concentration than the root cell inside.
- Yet the plant still needs to take minerals in — uphill.
- Root cells use active transport, spending ATP to pump minerals against the gradient.
Membrane transport is either passive or active. Passive transport moves substances down the gradient with no ATP (diffusion, facilitated diffusion, osmosis). Active transport uses ATP to pump substances against the gradient. The direction of travel — with or against the gradient — tells you which.