5.2 Factors Affecting Membrane Structure

Question 1

How does temperature affect membrane structure?

Answer 1

￪ temperature =

￪ E_k of phospholipids

Phospholipids vibrate more vigorously

Membrane disrupted, bigger gaps

￪ membrane permeability.

Carrier & channel proteins can denature >> ￬ membrane permeability

Question 2

If the temperature is increased, do phospholipids making up membranes denature?

Answer 2

no, only proteins (e.g channel proteins, carrier proteins) denature

membrane is said to be “disrupted”

Question 3

How does the type of solvent affect membrane structure?

Answer 3

• WATER - maintains membrane structure
  
  • Being polar, interacts with charged phosphate heads
  • Causes phosphate heads to face outwards & fatty acid tails inwards,
  • Forms bilayer with hydrophobic core
• ORGANIC SOLVENTS - dissolves membranes
  
  • Most are less polar than water
  • Cannot interact with phospholipids to keep phosphate heads outwards & fatty acid tails inwards
  • ∴ dissolves membranes
• PURE/STRONG ALCOHOL SOLUTIONS - dissolves membranes
  
  • Alcohol molecules are non-polar enough to enter phospholipid bilayer
  • High concentrations of alcohol solution disrupts/dissolves membrane

Question 4

5.2 Factors Affecting Membrane Structure

Describe & explain the effect of a water solvent on the structure of a membrane?

Answer 4

Water maintains membrane structure

Polar solvent, ∴ interacts with charged phosphate group on phospholipids

Causes phosphate heads to face outwards & fatty acid tails inwards

Forms bilayer with hydrophobic core

Question 5

The core of the phospholipid bilayer is [hydrophilic/hydrophobic], and therefore does not allow the simple diffusion of small, ____ molecules.

Answer 5

hydrophobic

polar

Question 6

Describe & explain the effect of an organic solvent on the structure of a membrane:

Answer 6

Dissolves membrane:

Most are less polar than water

Cannot interact with phospholipids to keep phosphate heads outwards & fatty acid tails inwards

Question 7

Organic solvents are [less/more] polar than water, so [can/cannot] maintain the structure of the phospholipid bilayer.

Answer 7

less

cannot

Question 8

Describe & explain the effect of a pure/strong alcohol solvent on the structure of a membrane:

Answer 8

Dissolves membrane:

Alcohol molecules are non-polar enough to enter phospholipid bilayer

High concentrations of alcohol solution disrupts/dissolves membrane

Question 9

Outline an experiment to investigate the effect of temperature on membrane permeability of beetroot cells:

Answer 9

1. Measure & cut cylinder of beetroot of equal size & surface area using cork borer.
2. Rinse the cubes with water to remove leaked betalain due to cutting.
3. Place each sample their own test tube of 10cm³ distilled water.
4. Place test tubes in water baths, each of varying temperatures (10°C, 20°C, 30°C, etc).
5. Leave for 15mins (time using stopwatch)
6. Remove beetroot samples & place solutions in colorimeter, measuring absorbance/transmission levels.
7. Repeat 3 times & calculate mean absorbance.
8. Plot a graph of absorbance against temperature. Higher absorbance, = more betalain leakage = greater disruption of membrane