Cell Membranes

Question 1

Describe the fluid mosaic structure.

Answer 1

Fluid as the phospholipids are constantly moving and mosaic as proteins are scattered through the bilayer.

Question 2

Name the components of the membrane.

Answer 2

Cholesterol, phospholipids, channel proteins, carrier proteins, receptor proteins, glycoproteins, glycolipids.

Question 3

What is the function of the cholesterol in the bilayer?

Answer 3

Fits between the phospholipids, bound do the hydrophobic tails, packing them close together, restricting the movement, making the eke brand more rigid - helps maintain shape of cell.

Question 4

How do you test the permeability of cell membranes?

Answer 4

1. Cut 5 equal pieces of beetroot rinsing them of pigment
2. Add each to a test tube full of 5cm3 of water measured using a pipette and measuring cylinder
3. Place each in a water bath at a different temperature (10,20,30,40,50)
4. Remove beetroot and leave coloured liquid and use a colorimeter to test how much light passes through and is absorbed - the higher the absorbance, the more pigment released so the higher the permeability.

Question 5

Describe how temperature increase, increases membrane permeability.

Answer 5

1. Below 0 phospholipids have little energy so can’t move much making the membrane rigid, but channel and carrier proteins deform increasing permeability.
2. Between 0-45 phospholipids can move and aren’t packed as tightly making the membrane partially permeable - as they move more permeability increases.
3. Above 45 phospholipids begins to break down making thee membrane more permeable, carrier and channel proteins deformation no so cannot control what goes in and out of the cells.

Question 6

Define diffusion.

Answer 6

Net movement of particles from an area of higher concentration to an area of lower concentration (passive process).

Question 7

What particles use facilitated diffusion?

Answer 7

Larger molecules as it would be too slow to diffuse regularly, charged particles as they are water soluble and the centre of the bilayer is hydrophobic.

Question 8

Define facilitated diffusion.

Answer 8

Moves particle don a concentration gradient from a higher to a lower concentration using channel or carrier proteins (passive process).

Question 9

How do carrier proteins work?

Answer 9

Large molecules attach to the carrier protein in the membrane causing it to change shape, allowing the molecule to be released on the opposite side of the membrane.

Question 10

How do channel proteins work?

Answer 10

Form pores in the membrane for charged particles to diffuse through down their concentration gradient. Different proteins facilitate different charged particles.

Question 11

What factors does diffusion depend on?

Answer 11

Concentration gradient, thickness of exchange surface and surface area.

Question 12

What factors does facilitated diffusion depend on?

Answer 12

Concentration gradient (up until a point) and number of channel or carrier proteins.

Question 13

Define osmosis.

Answer 13

Diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential.

Question 14

Define water potential.

Answer 14

The potential (likelihood) of water molecules diffusing in/out of a solution. Pure water has the highest water potential.

Question 15

Define isotonic.

Answer 15

When two solutions have the same water potential.

Question 16

What factors affect osmosis?

Answer 16

Water potential gradient, thickness of exchange surface, the surface area of the exchange surface.

Question 17

How do you conduct a serial dilution.

Answer 17

1. 5 test tubes in a test tube rack
2. 10cm3 of 2M solution in first test tube and 5cm3 of distilled water in the others
3. Use pipette to draw out 5cm3 out of first and put it in second test tube and mix thoroughly creating 1M solution
4. Repeat for other test tubes (0.5M,0.25M,0.125M)

Question 18

How do you find a scale factor and how is this useful?

Answer 18

Divide a known concentration by the concentration you want to make. The answer is how many times weaker you need to make the original solution, by using that amount times less of it. Top up with distilled water for desired volume.

Question 19

Define active transport.

Answer 19

Molecules and ions are transported across membranes using energy, usually against their concentration gradient.

Question 20

Describe how active transport works.

Answer 20

Molecule attached to carrier protein (binding site) causing it to change shape allowing the molecule to be released on the other side, against the concentration gradient. ATP undergoes hydrolysis splitting into ADP and Pi releasing energy so that molecules can be transported.

Question 21

Describe cotransport.

Answer 21

Cotransporters (carrier protein) bind two molecules at once, concentration gradient of one used to move the other molecule against its concentration gradient.

Question 22

What factors affect active transport?

Answer 22

Speed of individual carrier proteins, the number of carrier proteins, rate of respiration and thus the availability of ATP.