C4- Plasma Membranes

Question 1

4 functions of membranes

Answer 1

Site of chemical reactions

Partially permeable barrier

Cell communication

Compartmentalisation
–> not plasma/ cell surface membranes

Question 2

Compartmentalisation

Answer 2

The formation of separate membrane bound areas in a cell

Allows for specific conditions required for cellular reactions

maintains chemical gradients

Question 3

Membrane general structure

Answer 3

Phospholipid bilayer

hydrophilic heads form inner and outer surfaces of the membranes

Fatty acid tails form the core

Question 4

Fluid mosaic model

Answer 4

Phospholipids are free to move within the layer, giving it flexibility

Proteins in the layer form a mosaic like pattern

Question 5

Extrinsic protiens

Answer 5

embedded on one side of the bilayer or between layers

hydrophobic R group interacts with the hydrophilic heads

Question 6

Cholesterol

Membranes

Answer 6

Extrinsic protein

Regulates fluidity of membranes
–> adds stability to membranes without making them too rigid

Positioned between phospholipids

Question 7

intrinsic proteins

Answer 7

Transmembrane proteins embedded in both layers of proteins

channel and carrier proteins

Question 8

Channel vs carrier protiens

Answer 8

channel= allows passive movement of polar molecules and ions down a concentration gradient though membranes

carrier proteins= move against the concentration gradient
–> both passive and active transport

Question 9

membranes

Site of chemical reactions

Answer 9

membranes have to be in a particular position for chemical reactions to take place

Question 10

What happens when a membrane looses its structure

Answer 10

If they loose their structure, the cell’s processes will be disrupted

Question 11

Effect of high temperature on membranes

Answer 11

increased kinetic energy

Membrane become more fluid and looses its structure.
–> increasing its permeability

Carrier and channel proteins denature

Question 12

Effect of Solvent on membranes

water

Answer 12

water is polar and keeps bilayer intact

Question 13

Effect of alcohol on membranes

Answer 13

Less polar than water so can dissolve membranes, disrupting cells

Strong concentrations
–> dissolves membranes of bacterium
destroy cells in the body

less concentrated
–>alcohol enters the membrane but cannot dissolve it

Question 14

Diffusion

Answer 14

Passive net movement of particles from a high concentration to a low concentration, down a concentration gradient

Will continue to equilibrium

Question 15

Factors affecting rate of diffusion

Answer 15

Temperature
–> higher temp means particles have more kinetic energy

Concentration difference
–> greater difference= greater rate

Across membranes
- surface area, greater sa greater rate
- thickness of membrane, thin = greater rate

Question 16

Simple diffusion

Answer 16

Diffusion in the absence of a membrane or barrier

Question 17

Facilitated diffusion

Answer 17

Diffusion across a membrane using protein channels

Selective permeability

Question 18

The effect of temperature on membrane permeability PAG

Method

Answer 18

Beetroot PAG

Using a scalpel, cut five equal-sized cubes of beetroot

Rinse the beetroot pieces

Add the beetroot pieces to five different test tubes, each containing the same volume of distilled water

Put each test tube in a water bath at a different temperature (e.g. 10℃, 20℃, 30℃, 40℃, 50℃) for the same length of time

Remove the beetroot pieces, leaving just the coloured liquid in the five test tubes

Use a colorimeter to measure how much light is absorbed as it passes through each of the five samples of coloured liquid
–> higher the value, greater absorbance so more colour/pigment

Question 19

The effect of temperature on membrane permeability PAG

Limitations

Answer 19

Cuvettes may differ in thickness (very slightly). A thicker (or scratched) cuvette will absorb slightly more light than a thinner unscratched cuvette

The beetroot pieces may not be identical in size and shape, meaning some test tubes could contain slightly more beetroot tissue than others

Some parts of beetroot tissue have more pigment in their cells than others

Question 20

Active transport

Answer 20

The movement of molecules or ions into or out of a cell against the concentration gradient

Active process that requires energy provided by ATP and carrier proteins

Selective process- specific substances transported by specific carrier proteins

Question 21

Active transport

Process

Answer 21

Shape of carrier protein is complimentary to molecule they can carry

One way flow can only fit into carrier protein on one side of the membrane

Molecule binds

ATP binds to carrier protein inside cells

ATP- ADP which changes shape of a protein

Molecule transported across membranes

Phosphate detached and =recombines with ADP
–> protein reverts back original shape

Question 22

Why do cells performing active transport contain numerous mitochondria

Answer 22

To generate lots of ATP in aerobic respiration

Question 23

Why can glucose not pass through membrane by passive diffusion

Answer 23

Large molecule

therefore phospholipid bilayer acts as a barrier