5.2 - Factors affecting Membrane Structure

Question 1

What is the effect of temperature increase on plasma membranes?

Answer 1

• Increased temperature > increased kinetic energy in the plasma membrane
• More movement of the phospholipids making the bilayer more fluid - structure is lost and the cell breaks down
• Makes easier for particles to pass in and out of the cell
• This disrupts cell processes.

Question 2

What is the effect of carrier and channel proteins?

Answer 2

They denature at high temperature affecting membrane permeability

Question 3

Why are polar solvents important in bilayers?

Answer 3

Important in lipid bilayer formation as it keeps phosphate heads in water and fatty acid tails in the centre - keeps membranes intact.

Question 4

What are the effects of organic solvents?

Answer 4

• Less polar (alcohols, benzene) > they dissolve membranes and disrupt the cells
• Pure alcohol solutions are toxic = destroy cells
• Less concentrated alcohol (e.g. drinks) cause damage (don’t dissolve)
• Membrane becomes more fluid and permeable

Question 5

Why is it important to keep membranes intact?

Answer 5

Vital for specific functions such as nerve impulse transmissions

Question 6

State what can be used for a practical used to investigate membrane permeability and why

Answer 6

Use beetroot, contains betalain - red pigment released when membrane is disrupted.

Question 7

State the method used for a practical investigating membrane permeability.

Answer 7

1) Cut beetroot into equal sizes
2) Wash with distilled water to remove surface pigments, place in test tubes of 100cm3 distilled water in water bath
3) Pace each tube in a range of temperatures (10 degrees C intervals)
4) After 15 minutes take the solution out and measure absorbance using colorimeter
More abosrbance = more pigment molecules released.