Movement of substances into & out of cells

• Diffusion is the net movement of particles from an area of high to low concentration
• Osmosis is the net movement of water particles from an area of high to low water potential
• Active transport is the net movement of particles against a concentration gradient
• Factors affecting rate of movement of substances:

  • SA:V ratio- bigger cell means smaller SA:V ratio which slows the rate of diffusion
  • Diffusion distance- smaller distance means faster transport
  • Temperature- higher temperature means that molecules will move faster and collide with the cell membrane more often and therefore move across them faster
  • Concentration gradient- greater difference in concentration means that there will be faster movement across the membrane as on the side with higher concentration, there will be more collisions with the membrane
• Investigating diffusion:

  1. Cut 2 equally-sized beetroot cubes using a knife
  2. Make sure that the cubes are of the same dimensions
  3. Rinse the beetroot piece to get rid of any leaking pigment
  4. Put 5cm3 of water into two test tubes
  5. Keep one test tube at room temperature and one in a hot water bath at 90 degrees Celsius
  6. Leave the test tubes for two minutes and then add the beetroot
  7. Leave the test tubes for 10 minutes and then observe the results
• Investigating osmosis:

  1. Prepare a range of sucrose solutions with concentrations ranging from 0 to 1 mol/dm3
  2. Prepare 5 test tubes with different concentrations of sucrose solution
  3. Cut 6 equally-sized potato cubes, blot them and weigh each one
  4. Weigh each one and place one cube in each test tube
  5. After 4 hours blot the cubes and reweigh the cubes