Diffusion is the movement of molecules from an area of higher concentration to lower concentration, and occurs in all cells. Osmosis specifically refers to the diffusion of water molecules across a cell membrane. There are three types of osmosis depending on the concentration of water molecules inside and outside the cell: hypertonic occurs when more water leaves than enters the cell, hypotonic occurs when more water enters than leaves, and isotonic is when equal amounts of water move in and out of the cell.

1. OSMOSIS! Class Notes Monday, Sept. 20, 2010

2. Remember: What is the difference between diffusion and osmosis? Diffusion is: the movement of molecules from where there are many to where there are few Happens in all cells! Osmosis is: Diffusionof WATER across a cell membrane

3. Osmosis Why is it important? Cells contain water molecules and most cells are surrounded by water molecules If cells aren’t surrounded by mostly pure water, water will diffuse OUT. 3 different types of osmosis: Hypertonic Hypotonic Isotonic

4. Hypertonic solution When more molecules of water leave the cell than enter

5. Hypotonic solution When more molecules of water enter the cell than leave

6. Isotonic solution Iso = “the same” When molecules of water are moving in and out of the cell in equal amounts