Forms of transport

• Diffusion:

  Movement of -

  • Small
  • Non-polar
  • lipid soluble molecules

  CO2 + O2 are the smallest molecules that can move
• Facilitated diffusion:

  Movement of -

  • Larger than CO2
  • Polar
  • Water-soluble

  Channel proteins are needed
• Intrinsic proteins are channel + carrier
• Channel proteins:

  • Transport ions
  • Pore in the middle
  • Fills with water
  • Specific to ion
  • Specific shape
• Carrier proteins:

  • Larger molecules e.g. glucose + amino acids
  • Molecules bind to binding site
  • Changes shape of carrier protein
  • Flips molecule to other side of membrane
• Osmosis:

  Net movement of free water molecules form dilute solution to a concentrated solution cross a partially permeable membrane.

  Until equal on both sides

  In concentrated solution fewer free H2O:

  • Solute forms H bonds with H2O
  • Fewer free H2O to collide to move across cell membrane
• Active transport:

  • Against conc gradient
  • Pump
  • Needs energy from ATP to change shape of carrier protein
  • Hydrolysis of ATP makes it an accessible store of energy