Diffusion

• Diffusion

  The gradual movement of particles from places where there are lots of them to places where there are fewer of them
• Diffusion is really important in living organisms-it's how a lot of substances get in and out of cells
• Diffusion

  Spreading out of particles from an area of higher concentration to an area of lower concentration
• Diffusion happens in both solutions and gases because the particles in these substances are free to move about randomly
• The bigger the concentration gradient (the difference in concentration), the faster the diffusion rate
• A higher temperature will also give a faster diffusion rate because the particles have more energy and move around faster
• Cell membranes

  • Hold the cell together but let stuff in and out as well
  • Dissolved substances can move in and out of cells by diffusion
  • Only very small molecules can diffuse through cell membranes (e.g. oxygen, glucose, amino acids, water)
  • Big molecules like starch and proteins can't fit through the membrane
• Particles flow through the cell membrane

  From where there's a higher concentration to where there's a lower concentration
• The larger the surface area of the membrane, the faster the diffusion rate because more particles can pass through at once
• Osmosis

  The movement of water molecules through a partially permeable membrane from an area of lower solute concentration to an area of higher solute concentration
• Osmosis happens because there's a steady flow of water molecules from the area with lower solute concentration to the area with higher solute concentration
• Osmosis means that the water is trying to dilute the higher solute concentration