Biological Membranes

Question 1

What are some roles of membranes within cells

Answer 1

Compartmentalisation e.g. processes such as respiration
Site for chemical reactions e.g. rough ER
Form a concentration gradient

Question 2

What are some roles of cell surface membranes

Answer 2

Acts as a partially permeable barrier

Signal receptors

Question 3

Why is the phospholipid bilayer described as a fluid mosaic model

Answer 3

The phospholipids are able to move around giving the bilayer fluidity
The different types of proteins give a mosaic pattern

Question 4

What are phospholipids

Answer 4

A glycerol connected to a
2 hydrophobic fatty acid tails
1 hydrophilic phosphate head

Question 5

What is cholesterol’s function

Answer 5

Binds to the hydrophobic fatty acid tails and reduces fluidity by making the phospholipids pack more closely together

Question 6

What is cholesterol’s function

Answer 6

Binds to the hydrophobic fatty acid tails and reduces fluidity by making the phospholipids pack more closely together

Question 7

What are glycoproteins

Answer 7

They are intrinsic proteins with an attached carbohydrate embedded in the cell surface membrane
Acts as receptors for cell signalling
And binding sites for signalling molecules to bind to

Question 8

What are glycolpidsTh

Answer 8

They are lipids with attached carbohydrates

They are cell markers or antigens

Question 9

What are the 2 main types of intrinsic proteins embedded in the cell surface membrane

Answer 9

Channel proteins - allow polar molecules and ions to diffuse through the phospholipid bilayer

Carrier proteins - allow typically large molecules to pass through the membrane.
ATP sometimes involved

Question 10

How does temperature affect permeability
At really cold
At normal and as temp is increasing
At very hot

Answer 10

Really cold - Ice crystals will form and pierce the bilayer increasing permeability

At normal temperature the bilayer is partially permeable, fluid and stable

As temperature increases the phospholipids gain kinetic energy leaving temporary gaps for any molecules that diffuse through normally

If temperature increases further the bilayer may lose it’s stability and will become even more permeable. Proteins will start to denature so membrane will become completely permeable

Question 11

How does solvent affect permeability

Answer 11

Non-polar solvents can sit between fatty acid tails breaking H-bonds and disrupting the membrane
An increase in concentration will lead to an increase in permeability
e.g. alcohol wipes clean wounds by disrupting membranes of bacteria

Question 12

What is passive transport

Answer 12

Passive transport is the movement of a molecule from an area of high concentration to an area of low concentration .
This process doesn’t require the use of ATP

Question 13

What is simple diffusion

Answer 13

For example oxygen is non polar so it can diffuse from an area of high concentration to an area of low concentration

Question 14

What is facilitated diffusion

Answer 14

The movement of molecules with the aid of a channel or carrier protein.
For example large and polar molecules use this method

Question 15

What is osmosis

Answer 15

The net movement of water molecules from a high water potential to a low water potential across a partially permeable membrane

Question 16

How would you investigate osmosis with potato cells

Answer 16

Using same age of potato cut into equal lengths using a cork borer and a scalpel
You can alter your sucrose concentration using serial dilution or a dilution technique
Makes sure volume is the same
Record initial mass and put in solution for the same amount of time
Record final mass and calculate percentage change
More comparable
Where there is 0% change that’s the water potential

Question 17

How would you investigate the effect of temperature on membrane permeability

Answer 17

Cut samples of the same mass/length of beetroot
Leave to blot on paper so excess pigment is removed
Place each sample in a different temperature of water bath for the same amount of time
After remove the samples just leaving your coloured solutions
Looking can be subjective so using a calibration curve can help obtain a more accurate value
Using a red filter and a blank using colorimetry
Plot a graph of absorbance against temperature

Question 18

What is active transport

Answer 18

The net movement of molecules against its concentration difference and can also use membrane bound proteins that change shape to move molecules across the membrane
Both these processes require the use of ATP

Question 19

What is bulk transport and what are the two main types

Answer 19

Large molecules that are too large to fit through channel or carrier proteins
Endocytosis - Bulk transport of materials into cells
e.g. phagocytosis (solids) and pinocytosis (liquids)

Exocytosis - Unusually vesicles that are containing molecules move out of the Golgi apparatus and fuse with the cell surface membrane releasing its contents

Question 20

What water potential does pure water have how does increasing solute concentration have an effect?

Answer 20

0kPa so this means increasing solute concertation will decrease the water potential

Question 21

What does
Hypertonic
Isotonic 
Hypotonic 
mean when describing solutions

Answer 21

Hypertonic - Water potential is lower outside
Isotonic - Water potential is the same so net movement of water molecules is the same
Hypotonic - Water potential is higher outside

Question 22

How would an animal cell e.g. a red blood cell react to different solutions

Answer 22

Hypertonic - RBC would shrink, Hb is more concentrated so cell would have a dark look and
become crenated

Isotonic - RBC would have a normal appearance as water in = water out

Hypotonic - RBC would swell and burst - Cytolysis

Question 23

How would an plant cell react to different solutions

Answer 23

Hypertonic - Flaccid and if water further leaves becomes plasmolysis the plasma membrane
pulls away from the cell wall, the space is also filled with the external solution

Isotonic - There is no change

Hypotonic - The cytoplasm pushes the plasma membrane out against the cell wall making the
plant Turgid. The cell does not burst

Question 24

Why does the animal cell swell and burst but not the plant cell when placed in a hypotonic solution

Answer 24

Animal cell does not have a cellulose cell wall to withstand the high pressure