Active transport · ⁨主动运输⁩

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.

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

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

Comparing the three

• Diffusion and osmosis: high → low, no energy (passive 被动的).
• Active transport: low → high, needs energy (active).

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