RP3

• Cell-surface membranes


  Made up of a phospholipid bilayer which makes them selectively permeable
• Permeability


  Can be changed by different variables, such as temperature and concentration of solvents, like ethanol
• Beetroot cells


  Contain a purple pigment called betalain
• Higher permeability


  More pigment leaks out of cells
• Permeability measurement


  Amount of pigment leaked from beetroot cells into an aqueous solution using a colorimeter
• Investigating membrane structure


  1. Cut beetroot into identical cylinders

  2. Place cylinders in distilled water in water baths at range of temperatures

  3. Leave for 15 minutes

  4. Record temperature

  5. Remove beetroot, decant liquid, filter into cuvette

  6. Measure absorbance using colorimeter
• As temperature increases


  Permeability of cell-surface membrane increases
• Denaturation of proteins


  Heat damages bonds in tertiary structure, creating gaps in membrane
• At low temperatures


  Phospholipids have little energy, packed closely together, making membrane rigid, decreasing permeability
• At very low temperatures, ice crystals can form which pierce the cell membrane and increase permeability
• Investigating effect of ethanol

  1. Vary ethanol concentration as independent variable

  2. Ethanol causes cell-surface membrane to rupture, releasing betalain pigment

  3. Higher ethanol concentrations cause more disruption to membrane, forming more gaps, increasing permeability