Osmosis
Biology: Cambridge International GCSE Supplement, topic 3.2.2
Osmosis
Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.
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 (high water potential) on one side of a partially permeable membrane, but not many on the other side (low water potential), 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 high to low water potential.
Test yourself on Osmosis
Which of the following is a specialised plant tissue that uses osmosis to absorb water?