Tonicity and Osmoregulation
Introduced| English |
|---|
| osmosis/ɒzˈməʊsɪs/ |
| hypertonic/ˌhaɪpəˈtɒnɪk/ |
| hypotonic/ˌhaɪpəʊˈtɒnɪk/ |
| isotonic/ˌaɪsəˈtɒnɪk/ |
| osmoregulation/ˌɒzmɔːɡjʊˈleɪʃn/ |
Water on the move
- Cells sit in watery surroundings, and water crosses the membrane constantly.
- Too much water in and a cell swells; too much out and it shrivels.
- Which way water moves depends on what is dissolved on each side.
- Getting this balance right is a matter of life and death for a cell.
Osmosis: water follows solute
- Osmosis 渗透 is the diffusion of water across a membrane.
- Water moves toward the side with more dissolved solute.
- The membrane lets water through but blocks most of the solute.
- So water flows to even out the concentrations.
Osmosis is the movement of…
Osmosis is the diffusion of water across a membrane, from a dilute to a more concentrated solution.
Three kinds of surroundings
- Hypertonic 高渗的: more solute outside — water leaves, the cell shrinks.
- Hypotonic 低渗的: less solute outside — water enters, the cell swells.
- Isotonic 等渗的: solute equal both sides — no net water movement.
- Tonicity simply describes the outside compared with the cell.
Osmosis and tonicity
Set the outside solute concentration and watch which way water moves — toward the more concentrated side.
A cell placed in a hypertonic solution (more solute outside) will…
In a hypertonic solution water leaves the cell (toward the higher solute), so the cell shrinks.
In a hypotonic solution (less solute outside), a cell gains water and may burst.
Water enters toward the higher solute inside, so the cell swells and an animal cell may burst.
When the solute is equal inside and out, with no net water movement, the solution is ____.
In an isotonic solution the concentrations match, so there is no net osmosis.
Osmoregulation
- Osmoregulation 渗透调节 is how an organism controls its water balance.
- Your kidneys adjust how much water they keep or release.
- A freshwater fish constantly pumps out the water flooding in.
- Without this control, cells would swell or shrink out of action.
Select all true statements about tonicity.
Osmosis moves water, not salt. The other three are correct.
Water moves toward the side with more solute — that can feel backwards. Think "water follows salt": put a cell in salty (hypertonic) water and it loses water and shrinks, because water flows out toward the saltier side.
A red blood cell in pure water:
- Pure water is hypotonic — far less solute than inside the cell.
- Water rushes in toward the higher solute inside.
- With no cell wall to stop it, the animal cell swells and bursts.
Osmosis moves water across a membrane toward the more concentrated side. A hypertonic outside shrinks a cell, a hypotonic outside swells it, and an isotonic outside leaves it unchanged. Osmoregulation is how organisms keep their water balance steady.