5.2 factors affecting membrane structure (c)

Question 1

Describe the affect of increasing temperature on membrane structure

Answer 1

• phospholipids are constantly moving so an increase in temperature means an increase in kinetic energy, so the phospholipids move more
• the membrane becomes more fluid and begins to lose its structure
• too high temperatures will make it completely lose its structure so permeability increases, making it easier for more particles to cross
• carrier and channel proteins denature, affecting membrane permeability

Question 2

Describe water as a solvent for membranes

Answer 2

• water (solvent) allows the phospholipids to orientate - and the charged heads interact with water, helping to keep the bilayer intact

Question 3

Describe organic solvents like alcohols

Answer 3

• organic solvents are less polar than water, so will dissolve membranes, disrupting cells
• when the membrane is disrupted, it becomes more fluid and more permeable. some cells need intact cell membranes for specific functions e.g. neurone transmission

Question 4

Pros and cons of alcohols

Answer 4

• strong alcohol solutions = toxic - destroys body cells. can enter the cell membrane and disrupt it
• can be good - in antiseptic wipes - dissolve bacteria membrane in a wound, reducing the risk of infection

Question 5

Basis of investigating membrane permeability

Answer 5

• beetroot cells contain betalain - red pigment
• when beetroot cells membranes are disrupted, the betalain is released and surrounding solution is coloured
• amount of pigment released is related to disruption of cell membranes

Question 6

Describe the process of investigating membrane permeability

Answer 6

1. Cut pieces (5) of equally sized beetroot using a cork borer
2. Wash thoroughly in running water + place in 100ml distilled water in a water bath - increasing at 10°C intervals. Leave for 5 minutes.
3. Measure absorbances using colorimeter with a blue filter.
4. Repeat 3 times + calculate the mean and plot a graph