Types of Transport

• Simple Diffusion


  The net movement of particles from an area of high concentration to an area of low concentration

  Only occurs in liquids + gases --> Passive movement of particles
• Facilitated Diffusion:


  Large of charged ions will diffuse through carrier proteins or protein channels into the membrane.

  This is because they are water soluble and the centre of the bilayer is hydrophobic.
• Osmosis


  The net movement of water molecules from an area of higher water potential to an area of lower water potential across a semi-permeable membrane
• Isotonic


  Concentration inside and outside the cell is the same
• Hypotonic 


  Water potential of the solution is higher than the cell
• Hypertonic


  Water potential of the cell is higher than the solution
• Active Transport


  Requires energy (ATP -->Hydrolysed to -->ADP+Pi) across a concentration gradient.

  A carrier protein is used
• Co-transport


  Binds two molecules at the same time (carrier proteins)
• Co-transport Example


  Sodium ions are actively transported out of the cells into the blood by the sodium-potassium pump which creates a concentration gradient.

  This causes sodium ions to diffuse into the cell (They do this via the sodium-glucose co-transporter proteins)

  The co-transporter carries glucose into the cell with sodium and so thus the concentration of glucose inside the cell increases.

  Glucose diffuses out of the cell, into the blood (down the concentration gradient) through a protein channel by facilitated diffusion.