Active transport
Introduced| English | Meaning |
|---|---|
| active transport/ˈæktɪv ˈtrænspɔːt/ | The movement of substances across a cell membrane against their concentration gradient using energy and carrier proteins. |
| passive/ˈpæsɪv/ | passive |
Moving things the "wrong" way
- Sometimes a cell needs to take in a substance even when there's already more inside than outside.
- That means moving against the gradient — which needs energy. This is active transport 主动运输.
Active transport moves particles:
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Active transport goes against the gradient and needs energy.
The energy for active transport comes from:
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Respiration releases the energy used.
Active transport moves substances ______ the concentration gradient.
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From low to high concentration, unlike diffusion.
What active transport is
- Active transport is the movement of particles from a low to a high concentration (against the gradient), using energy.
- The energy comes from respiration.
Active transport moves particles against the gradient, using energy and a carrier protein
Active transport step by step
Step the carrier protein through its cycle: it uses energy from ATP to move a particle against the gradient, from low to high.
Active transport — pumping uphill
Unlike diffusion, active transport moves substances AGAINST the concentration gradient, so it needs energy.
Root hair cells use active transport to absorb:
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Minerals are scarce in soil, so they must be pulled in actively.
Why cells need it
- It lets cells absorb substances that are scarce outside.
- Root hair cells use it to take in minerals from very dilute soil water.
Water entering or leaving a plant cell makes it turgid, flaccid or plasmolysed
Diffusion and osmosis are passive (no energy), while active transport needs energy.
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Only active transport requires energy.
Comparing the three
- Diffusion and osmosis: high → low, no energy (passive 被动的).
- Active transport: low → high, needs energy (active).
Worked example. Soil has very little mineral salt, yet a root must absorb it. Diffusion can't help (it would go the wrong way), so the root hair cell uses active transport, powered by respiration, to pull minerals in.
You've got it
- active transport moves particles low → high concentration, using energy from respiration
- it absorbs substances that are scarce outside (e.g. minerals in roots)
- diffusion/osmosis are passive (no energy); active transport is active (needs energy)