Membrane permeability

• State 2 factors that affect the permeability of cell membranes.

  • Temperature

  • Concentration of solvents (ethanol)
• How is beetroot used to measure the permeability of cell membranes?

  The higher the permeability, the more red pigment that leaks out into the surrounding solution within a given time. A colorimeter can be used to determine the absorbance, hence concentration of pigment.
• Outline the procedure to investigate the effect of temperature on permeability of cell membrane.

  • Cut beetroot into 8 identical cubes with a scalpel.

  • Place each cube in a different test tube with equal volumes of distilled water.

  • Place each test tube into water baths ranging from 30-80°

  • Leave for 20 minutes.

  • Filter each solution out into a cuvette and measure the

  absorbance.
• What are the safety hazards involved in testing the effect of ethanol

  concentration on membrane permeability?

  • Ethanol is an irritant and is flammable, keep away from naked flames, wear eye protection.

  • Keep sharp scalpel away from fingers.

  • Handle hot liquid with care.
• What is the effect of temperature on membrane permeability?

  • Increasing temperature results in an increase in membrane

  permeability, as high temperatures denature some of the

  membrane proteins. This creates gaps in the membrane for

  molecules to pass through.

  • Decreasing temperature decreases the kinetic energy of

  phospholipids so they pack more tightly together, restricting the

  movement of molecules across the membrane.
• What is the effect of increasing ethanol concentration on membrane permeability?

  Increasing ethanol concentration leads to increased membrane permeability, as ethanol ruptures the membrane to form gaps for molecules to pass through.