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

with example

Answer 7

Transmembrane proteins embedded in both layers of proteins

channel and carrier proteins

Glycoproteins- used for cell signalling

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

general, strong conc, weak conc

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

Question 24

Water Potential

Answer 24

The pressure exerted by water as they collide with a membrane or container

The greater the amount of water (the more dilute the solution) the greater the water potential

Question 25

Water potential Values

Answer 25

pure water = 0kpa --> highest possible value All solutions have negative water potential, the more concentrated the solution the more negative the water potential

Question 26

Hydrostatic pressure

Answer 26

Increased pressure in a closed system such as a cell, due to diffusion of water.

Question 27

Animal cell in different water concentrations

Answer 27

Hypotonic= cytolysis isotonic= normal Hypertonic= crenated

Question 28

Plant cell in different water concentrations

Answer 28

Hypotonic= turgid isotonic= flaccid Hypertonic= plasmolysis --> cell membrane pulls away from cell wall, which keeps its structure. Solution fills the gaps made

Question 29

Osmosis

Answer 29

Osmosis is the net movement of water molecules through a partially-permeable membrane, from a region of high water potential to a region of low water potential.

Question 30

Roles of proteins in a cell surface membrane

Answer 30

glycoproteins- cell signalling and adhesion channel proteins- transport by facilitated diffusion; carrier proteins- active transport

Question 31

Membrane permeability PAG Why was it reliable and valid

Answer 31

valid- use the same beetroot, use cubes of the same size, same volume of water Reliable- repeat (at least) three times at each temperature, identify anomalies, calculate mean

Question 32

Explain why rate of diffusion increases as temperature increases

Answer 32

Increased temperature increases the kinetic energy of particles causing the particles to move at an increased speed

Question 33

State two changes to a cell surface membrane that would increase the rate that polar molecules diffuse into a cell

Answer 33

Increased surface area Decreased thickness

Question 34

Explain why facilitated diffusion is not a form of active transport

Answer 34

Diffusion is always a passive process, it does not require a metabolic energy source particle shave their own kinetic energy, moving down the concentration gradient In facilitated diffusion a channel/co-transport protein aids diffusion

Question 35

Why is it impossible to have a water potential above zero

Answer 35

The water potential of pure water is zero addition of solute decreases water potential therefore all solutions have negative water potential.

Question 36

Explain why its important to maintain concentration of electrolytes in the body to ensure proper hydration

Answer 36

Electrolytes/solutes/minerals are necessary for many body processes and help prevent excess water loss by osmosis To help maintain correct fluid balance for reactions

Question 37

Explain why glucose cannot pass through a cell membrane by simple diffusion

Answer 37

Phospholipids act as a barrier Molecule is too large Polar molecule due to polar OH groups- insoluble in bilayer

Question 38

Bulk transport

Answer 38

Movement of large molecules such as enzymes or hormones in or out of the cell Exocytosis Endocytosis

Question 39

Co transport

Answer 39

transport of one soluté against its concentration gradient in tandem with another that is diffusing down it's concentration gradient e. g H+ ions active transport via Proton pump alongside diffusion of sucrose