Diffusion

• All living things are made of cells which are differentiated to perform different functions
• Substances move into or out of the cell and enzymes are catalysts contributing to cell metabolism
• Diffusion


  The movement of particles from a region where they are in high concentration to a region where they are in low concentration, and is one of the ways substances can move across the cell membrane, into or out of the cell
• Concentration gradient


  The difference in the concentration of a chemical across a membrane
• Passive transport


  The movement of molecules down a concentration gradient without the need for additional energy, eg diffusion and osmosis
• Diffusion in living organisms


  • Products of digestion, dissolved in water, can pass across the wall of the small intestine by diffusion
  • Oxygen and carbon dioxide, dissolved in water, are exchanged by diffusion in the lungs
• Dissolved substances will only continue to diffuse while there is a concentration gradient
• Blood flow continuously takes oxygen away from the lungs, which helps to maintain the concentration gradient
• Alveoli


  Tiny air sacs in the lungs, where gas is exchanged during breathing
• Gas exchange in the lungs happens in the alveoli