Lesson 16 - Factors effecting membrane structure

Question 1

What are the factors that affect membrane structure:

Answer 1

• Temperature
• Solvents

Question 2

Effect of temperature:

Answer 2

• Phospholipids in a cell membrane are constantly moving
• When temperature increases, the phospholipids will have more kinetic energy and will move more.
• This makes the membrane more fluid and it begins to loose its structure. Gaps form between phospholipids.
• If temperature continues to increase, cell membrane will break down completely.

Question 3

Effect of temperature on permeability:

Answer 3

• Loss of structure.
• Easier for particles to cross.
• Carrier and channel proteins denature at higher temperatures.
• These are the proteins involved in transport across the membrane, membrane permeability will be affected.

Question 4

Why can solvents affect membrane structure:

Answer 4

• Water, a polar solvent, is essential for the formation of a phospholipid bilayer.
• Non-polar tails of the phospholipids are orientated away from the water, forming a bilayer with a hydrophobic core.
• Charged phosphate heads interact with water, helping to keep the bilayer intact.

Question 5

Organic solvents:

Answer 5

• Organic solvents are less polar than water.
  Eg. alcohols or non-polar benezene.
• Organic solvents dissolve membranes, disrupting cells.

Question 6

Use of organic solvents:

Answer 6

• Disrupt cells so used in antiseptic wipes.
• Alcohols dissolve the membranes of bacteria in a wound, killing them and reducing the risk of infection.

Question 7

Pure / strong alcohol solutions:

Answer 7

• Toxic as they destroy cells in the body.
• Less concentrated solutions (drink) will not dissolve membranes but still cause damage.
• Non-polar alcohol molecules enter the cell membrane and their presence between phospholipids disrupts bilayer.

Question 8

Effect of membrane disruption:

Answer 8

• More fluid and permeable
• Transmission of nerve impulses by neurones no longer possible.
• Neurones in brain disrupted, causing behaviour after alcohol.

Question 9

Practical:

Answer 9

• Beetroot cells contain betalain, a red pigment.
• When beetroot cells membranes are disrupted the red pigment is released and the surrounding solution is coloured. The amount of pigment released into the solution is related to the disruption of cell membranes.

Question 10

Steps:

Answer 10

1. 5 small pieces of beetroot cut equally with a cork borer.
2. Beetroot pieces thoroughly washed in running water.
3. They were then placed in 100 ml of distilled water in water bath (at 10 degrees intervals).
4. Wait 5 minutes for temperature of water bath to be reached in boiling tube.
5. Use colorimeter, with blue filter, to measure the concentration of betalain.
6. Repeat experiment 3 times to remove anomalies and calculate average.
7. Plot graph with temperature on the x axis and absorbance (blue light) on the y axis.