Osmosis
Biology: Edexcel IGCSE, topic 2.1.18
Osmosis
Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution (high concentration of water) to a concentrated solution (low concentration of water).
Partially permeable membrane
- A partially permeable membrane allows water through, but won't let larger molecules dissolved in water pass through.
Water movement
- Water will move to make the concentrations the same on both sides of the membrane:
- When there are lots of water molecules (in a dilute solution) on one side of a partially permeable membrane, but not many on the other side (in a concentrated solution), water will move from the dilute to the concentrated solution.
Net movement of water
- It is important to remember that water molecules will move through the membrane in both directions, but the net (overall) movement of water will be from the dilute solution to a concentrated solution.
Test yourself on Osmosis
Which of the following is a specialised plant cell that uses osmosis to absorb water?