Diffusion

Diffusion is the passive movement of particles from an area of high concentration to an an area of low concentration.

• Particles go through the cell membrane from where there are more particles (high concentration) to where there are less particles (low concentration)
• Particles move randomly so they go both ways, but the most movement tends to be away from the area of high concentration.
• The rate of diffusion is affected by the concentration difference. Substances diffuse faster if there is a bigger concentration difference, if there are lots more on one side then there are more to move across.

Osmosis is the movement of water molecules through a partially permeable membrane, from an area of high water concentration to an area of low water concentration.

• Water moves in and out of cells by osmosis.
• Tissue fluid is water with oxygen, glucose and other nutrients dissolved inside it.
• Through osmosis this water gets into the cell (via the membrane) because the cell has a low concentration of oxygen, glucose.