Osmosis
Osmosis
- Osmosis is a special diffusion: the net movement of water.
- It happens across a partially permeable membrane.
- It explains how plant cells become firm or floppy.
Practice
Osmosis is the net movement of:
Osmosis moves water only, through a partially permeable membrane.
What osmosis is
- Osmosis = net movement of water across a partially permeable membrane (water passes, larger solutes don't).
- Water moves from a region of higher water potential (dilute) to lower water potential (concentrated).
Practice
Water moves by osmosis from a region of:
Water moves down the water-potential gradient: from dilute (higher) to concentrated (lower).
Practice
A plant cell placed in pure water becomes:
Water enters by osmosis; the cell swells and the wall makes it turgid, supporting the plant.
Practice
A plant cell in a concentrated solution:
Water leaves by osmosis; the cell goes flaccid, and if more water leaves the membrane pulls away (plasmolysis).
Osmosis in plant cells
- in pure water / dilute solution: water moves in → the cell swells and becomes turgid (the wall stops it bursting) → this supports the plant.
- in a concentrated solution: water moves out → the cell becomes flaccid (soft); if more leaves, the membrane pulls away — plasmolysis.
You've got it
Key idea
- osmosis = net movement of water across a partially permeable membrane (higher → lower water potential)
- plant cell in dilute solution → turgid (firm, supports the plant)
- plant cell in concentrated solution → flaccid, then plasmolysed