5.2 Factors affecting membrane structure

Question 1

How does temperature affect the membrane?

Answer 1

Temperature increases the kinetic energy of the phospholipids and will begin to move more. This causes the membrane to become more fluid and it begins to lose its structure

If temperature continues to increase then the cell will eventually break down completely

Question 2

If a membrane begins to lose structure, what happens?

Answer 2

Loss of structure= increased permeability of the membrane, making it easier to cross

Carrier and channel proteins in the membrane will be denatured at higher temperature. As a result, the membrane permeability is affected

Question 3

Why is water important in forming the bilayer?

Answer 3

Water is a polar solvent that is essential in the formation of the phospholipid bilayer (Non-polar tails orientate away from water and thus form a hydrophobic core// Charged phosphate heads interact with water, keeping the bilayer intact)

Question 4

What effect does an organic solvent have on the membrane

Answer 4

Many organic solvents are else polar than water e.g. alcohol or non-polar like benzene.
–>These dissolve membranes and disrupt cells.

Pure/ very strong alcohols are toxic (destroys cells in body)

Question 5

How are alcohol wipes used to kill bacteria?

Answer 5

Less concentrated solutions of alcohols don’t dissolve membranes but still cause damage.
–> alcohol is used in antiseptic wipes where the alcohol dissolves the membrane of bacteria around a wound
–> killing them and reducing the risk of an infection

Question 6

Examples of when a membrane gets disrupted?

Answer 6

When membrane is disrupted, it becomes more fluid and more permeable.

Certain cells need intact membranes for specific functions e.g. transmission of nerve impulses by neurones (nerve cells)

Neuronal membranes disrupted= nerve impulses no longer transmitted as normal

Same problems with neurones in brain, causing behavioural changes

Question 7

Investigating membrane permeability:

Answer 7

Beetroot cells contain betalain (red pigment). When beetroot cell membranes are disrupted, the red pigment is released and the surrounding solution is coloured. (Amount of pigment released is related to disruption of cell membrane)

1. Cut 5 small pieces of beetroot of equal size using a cork borer. Wash thoroughly in running water and place in 100ml of distilled water in a water bath.
2. Increase the temperature of the water bath by 10 degrees Celsius intervals.
3. Take a sample of the water containing the beetroot after 5 minutes of each interval.
4. Measure the absorbance of each sample using a colorimeter with a blue filter
5. Repeat the experiment 3 times and record. The absorbance of each Fresh beetroot pieces.
6. Calculate the mean for each temperature.