5.2 Factors Affecting Membrane Structure

Question 1

Factors affecting membrane structure?

Answer 1

Temperature
Solvents
Cholesterol?

Question 2

How does temperature affect it?

If temperature increase …(2 ways)

Answer 2

• increased temperature increases kinetic energy of the already moving phospholipids , which means increased movement and thus increased fluidity .
• increased fluidity results in LOSS OF STRUCTURE, increasing PERMEABILITY OF THE CELL.
• increasing temperature means proteins found will eventually DENATURE, creating even more loss and structure and as those like CHANNEL AND CARRIER Affect transport this also increases permeability too.

Question 3

How does low temperatures affect membrane structure ?

Answer 3

Below zero phospholipids become closely packed together due to low kinetic energy

• this makes membrane rigid
• ice crystals Formed can PUNCTURE the membrane too INCREASING PERMEABILITY HERE
• finally proteins denature at LOW TEMPS ASWELL, affecting permeability in the ways stated before

Question 4

Why is water vital to do formation of a bilayer

Answer 4

Being polar means heads can orientate them in ways that a bilayer is formed

Question 5

How do organic solvents like alcohol affect membranes

Answer 5

Substances less polar than water like alcohol or non polar like benzene will DISSOLVE MEMBRANES

Does this by

• enter cell membranes and makes it LOSE STRUCTURE, gain FLUIDITY
• thus GAIN PERMEABILITY

Question 6

How can you use this to explain behaviour in people and also real life practices of it

Answer 6

1) antiseptics will have alcohols as these dissolve membranes of bacteria and KILL THEM
2) alcohol can enter neurones cells, which if get disrupted can not function as well, which explains people’s behaviour after consuming alcohol

Question 7

How to investigate effect if temperature on membrwne permeability through beetroot?

Answer 7

• beetroot contains red pigment betalain that gives them their colour
• more permeable a membrane becomes the more will be leaked out
• pieces of equal beetroot after being blotted for excess dye olaced in distilled water tubes and heated at different temperatures in water baths
• after few minutes taken out and shaken and beetroot discs removed .
• then colorimeter test taken to see more absorbance / less transmission

Question 8

Why does amount of colour change after a while?

Answer 8

At the start increase temperature = loss of structure = more permeable
BUT
at certain temp the permeability jumps , this because various proteins denaturier, resulting in more loss of structure but also as they affect transport kore permeable

Question 9

How to improve practical

Answer 9

Cut pieces from same place using better equipment

• blot surface of beetroot before experiment
• same volume of water
• use control AT ALL TEMPS
• smaller temperature ranges