Core Practical 3

• What are cell-surface membranes primarily made of?

  Phospholipid bilayer
• What does selectively permeable mean in relation to membranes?

  It allows certain substances to pass through
• Which variables can change membrane permeability?

  Temperature and concentration of solvents
• How can the permeability of a membrane be measured?

  Using beetroot cells and betalain pigment
• What happens to the pigment when the membrane has higher permeability?

  More pigment leaks out of cells
• What is the name of the pigment found in beetroot cells?

  Betalain
• What equipment is used to measure the amount of pigment leaked?

  A colorimeter
• What equipment is needed for the experiment?

  • Water baths
  • Thermometer
  • Distilled water
  • Syringe
  • Beetroot
  • Cork borer
  • White tile
  • Knife
  • Pipette
  • Test tubes
  • Colorimeter
  • Cuvettes
  • Forceps
• What is the first step in the method for measuring membrane permeability?

  Cut beetroot into 8 identical cylinders
• How long should the beetroot samples be left in distilled water?

  15 minutes
• What should be done after removing the beetroot cylinders from the test tubes?

  Decant the liquid into clean test tubes
• What is the purpose of setting the colorimeter to a blue filter?

  To measure absorbance of the pigment
• What does a higher absorbance indicate in the experiment?

  Higher pigment concentration and permeability
• What are the risks associated with the experiment?

  • Cuts from scalpel
  • Cuts from broken glass
  • Scalding from hot liquids
  • Irritation from ethanol
• What safety precaution should be taken when using a scalpel?

  Cut away from fingers
• What should be done in case of a cut from a scalpel?

  Elevate cuts and apply pressure
• What happens to membrane permeability as temperature increases?

  It also increases
• Why does membrane permeability increase with temperature?

  Proteins denature and create gaps
• What occurs at low temperatures regarding phospholipids?

  They have little energy and are packed closely
• What can form at very low temperatures that affects permeability?

  Ice crystals can pierce the membrane
• How can the method be modified to investigate ethanol's effect on permeability?

  • Use ethanol concentration as the independent variable
  • Higher ethanol concentrations cause more membrane disruption
  • More gaps form, increasing permeability
• What is the effect of higher concentrations of ethanol on the cell membrane?

  They cause more disruption and gaps
• What is the relationship between ethanol concentration and membrane permeability?

  As ethanol concentration increases, permeability increases