Plasma membranes

Question 1

What are some functions of the phospholipid bilayer?

Answer 1

• Compartmentalisation
• Site of chemical reactions
• Acts as a barrier

Question 2

Describe a carrier protein

Answer 2

• Intrinsic
• Changes shape to allow substances across
• Does facilitated diffusion and active transport
• Selective (specific proteins for certain substances)

Question 3

Describe a channel protein

Answer 3

• Instrinsic
• Facilitated diffusion
• Allows polar substances like important ions and water through
• Selective

Question 4

What bonds hold together fatty acids in a phospholipid bilayer?

Answer 4

Weak intermolecular forces
- Stabilise the whole structure

Question 5

What factors affect membrane structure?

Answer 5

Temperature - Increases kinetic energy, so intermolecular forces vibrate more and break apart. Protein channels/carriers also denature. Permeability increases as a result of all this, more gaps.
Non polar solvents - eg ethanol disrupts bilayer increasing permeability and fluidity as the membrane breaks

Question 6

What is facilitated diffusion?

Answer 6

• Diffusion across a protein channel on plasma membrane
• Selectively permeability

Question 7

What 4 factors increase diffusion rate?

Answer 7

• Temperature
• Concentration gradient
• Surface area:Volume ratio
• Thin membrane - decreased diffusion distance

Question 8

What is water potential measured in?

Answer 8

Pascals (Pa)

Question 9

What is the difference between a hypertonic and hypotonic solution?

Answer 9

Hypertonic - Comparatively more solute and less water, so lower water potential. Water moves out of cell, into solution
Hypotonic- Opposite

Question 10

What happens to an animal and plant cell when lots of water leaves and when water enters?

Answer 10

Animal -
Leaves (hypertonic) - Becomes shrivelled, crenated.
Enters (hypotonic) - Bursts, undergoes lysis
- -
Plant -
Leaves - Plasmolysis, plasma membrane detaches from cell wall
Enters - Turgid, plasma membrane pushes against cell wall but doesn’t burst

Question 11

Describe the practical investing the effect of temperature on membrane permeabbility

Answer 11

• Beetroot cells contain belatin which is a red pigment giving them a distinct colour
• When beetroot plasma membrane’s are disrupted, belatin is released and the sourrounding solution is coloured
• Five pieces of beetroot should be placed in distilled water inside a water bath, with the temperature increased in 10 degree intervals
• Samples from each temperature have their absorbance measured with a colorimeter with a blue filter.
• Measured in arbitury units