Beetroot Permeability

• Cell-surface membranes, comprising a phospholipid bilayer, are selectively permeable.

  • Permeability, affected by factors like temperature and solvent concentration (e.g., ethanol), can be altered.
  • Beetroot cells, containing betalain pigment, demonstrate membrane permeability changes.
  • Permeability is quantified by measuring pigment leakage into an aqueous solution using a colorimeter
• channel vs carrier

  • Channel = passive, Carrier = active+passive
  • Channel = don't change shape, Carrier = change shape
• Method

  1. Cut beetroot into 8 identical cylinders + clean to remove any released pigment.
  2. Place beetroot cylinders in 10 ml of distilled water in test tubes at various temperatures (0-70°C).
  3. Incubate samples for 15 minutes to allow pigment leakage.
  4. Record the temperature of the water bath.
  5. Remove beetroot cylinders, decant liquid into clean test tubes.
  6. Set colorimeter to blue filter, zero with distilled water, then filter each sample into a cuvette.
  7. Measure absorbance for each solution; higher absorbance indicates higher pigment concentration, indicating a more permeable membrane.
  8. Plot graph
• Ethanol


  causes the cell-surface membrane to rupture, releasing the betalain pigment from the cell.
• Effect of increased temperature on membrane permeability

  High temperature increases the kinetic energy of phospholipid molecules in the cell membrane, causing them to move more rapidly.

  • This increased movement disrupts the bonds between neighboring phospholipids,
  • and proteins denature as heat damages the bonds in their tertiary structure

  leading to greater membrane fluidity and gaps in membrane
• Effect of low temperature on membrane permeability

  At low temperatures, phospholipids are tightly packed due to reduced kinetic energy, resulting in a rigid membrane with decreased permeability.

  • However... at very low temperatures, ice crystals can form and puncture the cell membrane, increasing permeability.