Mechanisms of Transport
Introduced| English |
|---|
| pump/pʌmp/ |
| endocytosis/ˌendəʊsɪˈtəʊsɪs/ |
| vesicle/ˈvesɪkl/ |
| exocytosis/eɡˌzɒsɪˈtəʊsɪs/ |
Pumping and hauling
- Sometimes a cell must move a substance the "wrong" way — against its gradient.
- Sometimes the load is far too big for any protein doorway.
- For both jobs, the cell spends energy and uses clever machinery.
- These are the active mechanisms of transport.
Protein pumps
- A pump 泵 is a carrier protein that moves ions against their gradient.
- It spends ATP to change shape and push the ion uphill.
- The sodium-potassium pump keeps nerve and muscle cells ready to fire.
- Without pumps, a cell could never build up ions above its surroundings.
A protein pump moves ions against their gradient using…
A pump is active transport: it spends ATP to move ions from low to high concentration.
Endocytosis: taking it in
- For big loads, the cell uses its membrane like a net.
- In endocytosis 胞吞作用 the membrane wraps around material and pinches inward.
- This forms a vesicle 囊泡 — a small bubble — carrying the load inside.
- This is how a cell can swallow something as big as a whole bacterium.
A protein pump in action
Step the pump through its cycle — it spends ATP to move a particle against the gradient, from low to high.
In endocytosis, the cell…
Endocytosis takes material in by wrapping the membrane around it to form a vesicle.
Exocytosis: sending it out
- The reverse process ships material out of the cell.
- In exocytosis 胞吐作用 a vesicle moves to the membrane and fuses with it.
- Its contents spill to the outside.
- This is how cells release hormones, enzymes, and waste.
Releasing material by fusing a vesicle with the membrane is called ____.
In exocytosis a vesicle fuses with the membrane and dumps its contents outside.
Endocytosis and exocytosis move materials too large to fit through a membrane protein.
Bulk transport handles large loads — like whole cells or big molecules — that no channel could pass.
Select all true statements about transport mechanisms.
Pumps are active transport and do need ATP. The other three are correct.
Pumps, endocytosis, and exocytosis all cost energy. Unlike diffusion, they can move things against a gradient or move loads too big for any channel — but the cell must pay for all of it with ATP.
A white blood cell eating a germ:
- The germ is far too big to fit through any membrane protein.
- The white blood cell flows its membrane around the germ (endocytosis).
- The germ is sealed inside a vesicle, then destroyed — how your body fights infection.
Active mechanisms move things diffusion cannot. A pump spends ATP to push ions uphill. Endocytosis wraps the membrane around a large load to bring it in as a vesicle; exocytosis fuses a vesicle with the membrane to release material out. All three cost energy.