required practical 4 - permeability of cell-surface membrane

• • method for temperature variables:

  1. cut beetroot into 6-10 identical cubes using a scalpel
  2. wipe to clean off any pigment
  3. place each test tube in a water bath at a range of temperatures ( 30-80 degrees)

  • method for concentration of ethanol:

  1. create a dilution series of ethanol using distilled water (0-100%)
  2. leave the samples for 20 minutes
  3. set the colorimeter to a blue filter & 0 using a cuvette with distilled water
  4. filter each sample into a cuvette using filter paper
  5. measure the absorbance for each solution
• why should the sample be left for 20 minutes?

  so the pigment can leak out the beetroot
• what does a higher absorbance indicate?

  a higher pigment concentration & so a more permeable membrane
• what is the conclusion of this method?

  temperature:

  • as temperature increases, the permeability of the cell-surface membrane increases. This is because the proteins in the cell-surface membrane denature as the heat damages the bonds in the tertiary structure & this creates gaps in the membrane, making it easier for molecules to pass through
  • at low temperatures, phospholipids have little energy & are packed closely together to make the membrane more rigid, causing a decrease in permeability
• what is the conclusion of this method?

  concentration of ethanol:

  • ethanol causes the cell-surface membrane to rupture, releasing the pigment. Higher concentrations of ethanol will cause more disruption to the membrane & more gaps will form
  • so as concentration of ethanol increases, the permeability of the cell-surface membrane also increases