Osmosis is a specific type of diffusion - it is the movement of water particles from an area of higher water potential to an area of lower water potential, across a partially permeable membrane.
Water potential is how likely water molecules are to diffuse into or out of a solution. Pure water has a water potential of 0, adding any solutes to the water lowers the water potential - meaning that the water potential of a solution is always negative.
Definitions:
Isotonic solutions are solutions which have the same water potential, meaning that there will be no movement of water.
Hypotonic solutions are solutions which have a higher water potential compared to the inside of a cell.
Hypertonic solutions are solutions that have a lower water potential than the inside of a cell.
What affects the rate of osmosis?
- Water potential gradient - higher water potential gradient, faster rate of osmosis
- Thickness of exchange surface - thinner exchange surfaces, faster rate of osmosis
- Surface area - larger surface area, faster rate of osmosis