Osmosis
Introduced| English | Meaning |
|---|---|
| osmosis/ɒzˈməʊsɪs/ | The net movement of water molecules through a partially permeable membrane from higher to lower water potential. |
| dilute/daɪˈluːt/ | dilute |
| partially permeable membrane/ˈpɑːʃəli ˈpɜːməbl ˈmembreɪn/ | A barrier that allows some substances to pass through but restricts others. |
| turgid/ˈtɜːdʒɪd/ | Describing a plant cell swollen and firm because water entering by osmosis produces pressure against its cell wall. |
| flaccid/ˈflæsɪd/ | Describes a plant cell or plant that has lost water and gone soft. |
| wilts/wɪlts/ | Droops when cells lose turgor through lack of water. |
The special case of water
- Water also moves by diffusion — but because it's so important, it gets its own name: osmosis 渗透.
- It explains why plants wilt, why cells burst, and how roots drink.
Osmosis is the net movement of:
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Osmosis is specifically water across a partially permeable membrane.
Osmosis requires energy from the cell.
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Like diffusion, osmosis is passive.
Osmosis happens across a partially ______ membrane.
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It lets water through but not larger solute particles.
What osmosis is
- Osmosis is the net movement of water molecules from a dilute 稀的 solution (high water concentration) to a concentrated solution (low water concentration), through a partially permeable membrane 半透膜.
- Like diffusion, it needs no energy.
Osmosis: water crosses the partially permeable membrane; solute is held back
Osmosis
net movement down the gradient
A difference in concentration drives net movement until both sides are equal.
An animal cell placed in pure water will:
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Water enters by osmosis, swelling the cell.
Osmosis in cells
- A cell in pure water gains water and swells (an animal cell may burst).
- A cell in a concentrated solution loses water and shrinks.
Red blood cells: water moves in and out of cells by osmosis
A plant cell full of water and firm is described as:
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Turgid cells support the plant; flaccid cells cause wilting.
Why plants need it
- Plant cells take in water by osmosis and become turgid 膨胀 (firm), supporting the plant.
- Without enough water, cells become flaccid 松软 and the plant wilts 萎蔫.
Osmosis only moves water. Diffusion can move any particle; osmosis is specifically water across a partially permeable membrane. Keep the two ideas distinct.
You've got it
- osmosis = net movement of water from dilute → concentrated, through a partially permeable membrane
- it needs no energy (it's a special case of diffusion)
- plant cells become turgid (firm) when full of water, flaccid when short