Transport in Cells

• Diffusion


  The net movement of particles from an area of higher concentration to an area of lower concentration
• Substances that can move in and out of cells via diffusion


  • O2 diffuses into red blood cells
  • CO2 diffuses out from red blood cells
• Factors that affect the rate of diffusion


  • Temperature
  • Concentration gradient
  • Surface area
• Osmosis


  The diffusion of water across a partially permeable membrane from a high concentration of water to a low concentration of water
• The partially permeable membrane allows water to diffuse through, but won't let larger molecules dissolved in water pass through
• During osmosis, water moves from a dilute solution to a concentrated solution
• Active transport

  The net movement of particles against a concentration gradient, which requires energy
• Active transport


  Requires energy, whereas diffusion and osmosis do not require energy
• Diffusion and osmosis are 'passive'
• Exchange surfaces


  • Adapted to maximise the efficiency of gas and solute exchange
  • Have a large surface area to allow more of a substance to diffuse at the same time
  • Have thin membranes to reduce the diffusion distance