Cell Membranes

Question 1

what are the functions of membranes?

Answer 1

cell surface membrane
compartmentalisation
control of exchange molecules
cell signalling
cell adhesion

Question 2

what is the purpose of the plasma membrane?

Answer 2

separates cell from its external environment

Question 3

what is the purpose of compartmentalisation?

Answer 3

contains reactions in separate parts of cell which allows specific conditions for reactions to be maintained

Question 4

how do cell membranes control the exchange of molecules?

Answer 4

partially permeable membrane - only small and non polar molecules can diffuse through
it also creates a conc gradient

Question 5

how do cell membranes perform cell signalling?

Answer 5

hormones can bind to receptors on plasma membrane and stimulate a response at synapse

Question 6

what is the purpose of cell adhesion?

Answer 6

so cells can stick together to form tissues

Question 7

name the components of cell membranes

Answer 7

phospholipids
proteins (intrinsic and extrinsic))
cholesterol
glycolipids
glycoproteins

Question 8

what is the function of cholesterol?

Answer 8

regulates the fluidity of membranes

Question 9

how does cholesterol regulate the fluidity of the membrane?

Answer 9

adds stability by its hydrophilic end interacting with the heads and its hydrophobic end interacting with tails, pulling them together
prevents membranes becoming too solid by stopping the phospholipid molecules from grouping too closely and crystallising

Question 10

what is the function of glycolipids?

Answer 10

they are cell markers/antigens
so they can be recognised by cells of the immune system

Question 11

what are glycolipids?

Answer 11

lipids with an attached carbohydrate chain

Question 12

what are glycoproteins?

Answer 12

intrinsic proteins with an attached carbohydrate chain

Question 13

what is the function of glycoproteins?

Answer 13

cell adhesion
receptors for chemical signals - eg for peptide hormones eg insulin

Question 14

what is the function of channel proteins?

Answer 14

provide hydrophilic channel that allows passive movement of polar mols/ions

Question 15

what is the function of carrier proteins?

Answer 15

protein changes shape
involved in passive and active transport

Question 16

how does temp affect the membrane?

Answer 16

higher temp = more kinetic energy = phospholipids move around more = more gaps in bilayer = increase in permeability
however temp too high = denature of proteins in membrane = membrane breaks down

Question 17

how does pH affect the membrane?

Answer 17

outside optimum pH (higher or lower) proteins in membrane denature = membrane breaks down so becomes fully permeable

Question 18

how do solvents such as ethanol affect the membrane?

Answer 18

ethanol dissolve lipids - more ethanol means more phospholipids dissolve so membranes become more permeable - membrane breaks down so becomes fully permeable

Question 19

why is it known as the fluid mosaic model?

Answer 19

fluid - phospholipids are constantly moving
mosaic - proteins are scattered like a mosaic

Question 20

define passive

Answer 20

doesn’t require energy from respiration/ATP

Question 21

define diffusion

Answer 21

the net movement of molecules down the conc gradient from an area of higher conc to an area of lower conc

Question 22

name the factors affecting the rate of diffusion

Answer 22

SA:V
conc gradient
temp
diffusion dist

Question 23

how does SA:V affect the rate of diffusion?

Answer 23

higher ratio = higher rate of diffusion

Question 24

how does conc gradient affect the rate of diffusion?

Answer 24

steeper gradient = faster rate of diffusion

Question 25

how does temp affect the rate of diffusion?

Answer 25

higher temp = higher rate (more kinetic energy)

Question 26

how does diffusion distance affect the rate of diffusion?

Answer 26

shorter distance = higher rate

Question 27

define facilitated diffusion

Answer 27

diffusion of polar molecules/ions across a membrane through protein channels/carrier proteins

Question 28

what other factor affects the rate of facilitated diffusion?

Answer 28

number of channel proteins present

Question 29

define osmosis

Answer 29

the movement of water molecules down the water potential gradient, through a partially permeable membrane

Question 30

define water potential

Answer 30

the pressure exerted by water molecules as they collide with the container/molecule

Question 31

how is water potential measured

Answer 31

kilopascals (kPa)

Question 32

what is the water potential of pure water?

Answer 32

0kPa

Question 33

what is the approx width of a plasma membrane

Answer 33

7nm

Question 34

define cytolysis

Answer 34

when an animal cell bursts due to increased pressure

Question 35

define crenation

Answer 35

when an animal cell shrivels due to reduced volume

Question 36

define turgid

Answer 36

when the plant cell swells so protoplast pushes against cell wall

Question 37

define plasmolysis

Answer 37

when the plant cell shrinks so the protoplast is completely pulled away from the cell wall

Question 38

define active transport

Answer 38

movement of molecules from an area of lowER conc to an area of highER conc - requires energy and carrier proteins

Question 39

why is active transport described as selective?

Answer 39

specific substances are transported by specific carrier proteins

Question 40

what is bulk transport?

Answer 40

a form of active transport which moves larger molecules in and out of the cell eg enzymes, hormones, bacteria

Question 41

define endocytosis

Answer 41

the bulk transport of material into cells (phagocytosis for solids and pinocytosis for liquids)

Question 42

describe endocytosis

Answer 42

plasma membrane invaginates (bends inwards) when it comes into contact with material membrane enfolds material until it fuses, forming a vesicle vesicle pinches off and moves into cytoplasm to transfer the material for further processing

Question 43

define exocytosis

Answer 43

bulk transport of material out of cells