2.5.2 Structure and Permeability

• What factors affect the permeability of cell membranes?

  Temperature and solvent concentration
• How does temperature affect the fluidity of lipids in cell membranes?

  As temperature increases, lipids become more fluid
• What happens to polar molecules as membrane fluidity increases?

  Polar molecules can pass through the membrane more easily
• What effect does increased temperature have on diffusion through the cell membrane?

  Diffusion occurs at a higher speed due to increased kinetic energy
• Are changes in membrane fluidity reversible?

  Yes, changes in membrane fluidity are reversible
• What happens to lipids when temperatures decrease?

  Lipids return to their normal levels of fluidity
• At what temperature do many proteins in cell membranes begin to denature?

  At around 40°C
• What is the consequence of protein denaturation in cell membranes?

  It disrupts the membrane structure, making it ineffective as a barrier
• What happens to substances when the membrane structure is disrupted?

  Substances can pass freely through the disrupted membrane
• How do organic solvents affect cell membrane permeability?

  They increase permeability by dissolving the lipids in the membrane
• How can you investigate the effect of temperature on membrane permeability using beetroot?

  • Cut equal-sized cubes of beetroot
  • Rinse to remove pigment
  • Place in test tubes with equal water volumes
  • Heat at different temperatures (e.g., 10°C to 50°C)
  • Measure pigment leakage using a colorimeter
• What apparatus is needed to investigate membrane permeability using beetroot?

  Scalpel, cork borer, cutting board, ruler, test tubes, water baths, stopwatch, colorimeter
• Why is it important to cut beetroot pieces to the same size?

  To ensure equal surface areas and volumes for accurate results
• What is the expected result when temperature increases during the experiment?

  Membrane permeability increases
• What happens to phospholipids as temperature increases?

  They move more due to increased energy
• What effect does high temperature have on the phospholipid bilayer?

  It may start to melt and break down
• How does temperature affect channel and carrier proteins in the membrane?

  High temperatures can cause them to deform
• What happens to cell membranes at very low temperatures?

  They can become damaged and highly permeable upon thawing
• What are the limitations of using beetroot to investigate membrane permeability?

  • Cuvettes may differ in thickness
  • Beetroot pieces may not be identical in size
  • Different parts of beetroot have varying pigment concentrations
• What is a suggested solution to the limitation of cuvette thickness in colorimetry?

  Use the same cuvette for every reading
• How can you ensure beetroot pieces are identical in size?

  Cut them as accurately as possible using a scalpel and ruler
• What is a method to address the variability in pigment concentration in beetroot tissue?

  Conduct several repeats using different parts of the beetroot
• How can solvent concentration affect cell membrane permeability?

  By placing beetroot pieces in increasing concentrations of solvents