2b (cell membranes)

Question 1

role of the cell membrane

Answer 1

acts as a barrier between cell and the environment and controls what enters and leaves the cell

Question 2

what does fluid mosaic structure mean?

Answer 2

it shows how phospholipid molecules form a continuous bilayer
it is fluid as phospholipids are flexible and constantly moving
it is mosaic because proteins imbedded vary in shape/ size/ pattern

Question 3

what does cholesterol do in membranes?

Answer 3

gives stability
makes membranes less fluid (bind to phospholipid tails so restrict movement)
prevents leakage of water and dissolved ions
maintain shape of animal cells
cold temp- membrane likely to fracture but cholesterol prevents it
hot temp- stop it from becoming too fluid

Question 4

what do glycoproteins do in membranes?

Answer 4

recognition sites
help cells attach to form tissues

Question 5

what do glycolipids do in membranes?

Answer 5

recognition sites
maintain stability of membrane
help attach cells
cell surface receptors

Question 6

what are protein receptor sites?

Answer 6

allow other proteins to attach due to complimentary shape
send signals

Question 7

what do channel proteins do?

Answer 7

allow water soluble ions to diffuse by facilitated diffusion

Question 8

what do carrier proteins do?

Answer 8

bind to ions/molecules to change their shape- active transport

Question 9

does a low temp increase or decrease permeability? why?

Answer 9

increase as ice crystals may form and pierce the membranes
but
rigid as phospholipids dont have much energy

Question 10

permeability of a membrane at 0-40 degrees

Answer 10

partially permeable as phospholipids can move. increases as phospholipids gain more energy

Question 11

does a high temp increase or decrease permeability of membrane?

Answer 11

increase as bilayer begins to break down
water moves in which puts pressure on membrane
channel and carrier proteins deform so cant control what enters/leaves and permeability increases

Question 12

what is simple diffusion and examples of things that do this

Answer 12

molecules passing straight through the membrane
eg oxygen and carbon dioxide

Question 12

what is diffusion?

Answer 12

net movement of particles from area of higher concentration to an area of lower concentration. passive

Question 13

what is facilitated diffusion and examples of things that do this

Answer 13

large/charged particles diffusing through carrier/channel proteins
still down conc gradient
eg larger molecules (amino acids, glucose), charged particles (ions, polar molecules)

Question 14

why cant larger molecules simply diffuse?
why cant charged particles simply diffuse?

Answer 14

too big so diffuse slowly
they are water soluble and centre centre of bilayer is hydrophobic so diffuse slowly

Question 15

carrier proteins job and how they do this

Answer 15

move large molecules across membranes
1) large molecule attaches (diff protein for diff molecule)
2) protein changes shape
3) released on opposite side of membrane

Question 16

channel proteins job

Answer 16

form pores in membrane for charged particles to diffuse through
diff protein for diff particle

Question 17

what does rate of simple diffusion depend on?

Answer 17

conc gradient- higher means faster but slows over time as reach equilibrium
thickness of exchange surface- thinner means faster (shorter path to travel)
surface area- larger means faster eg microvilli increase sa by about 600x so more particles exchanged in same time

Question 18

what does rate of facilitated diffusion depend on?

Answer 18

conc gradient- higher means faster until equilibrium reached
number of channel/ carrier proteins- once all in use, rate cant increase so more proteins means faster

Question 19

what are aquaporins?

Answer 19

channel proteins that allow facilitated diffusion of water through cell membranes. some kidney cells have lots
they allow cell to reabsorb a lot of water otherwise excreted

Question 20

what is osmosis?

Answer 20

(net) movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane

Question 21

what is water potential? units?

Answer 21

potential/ likelihood of water molecules to diffuse into or out of a solution
KPa

Question 22

does pure water have a high or low water potential? what happens as you add more solute?

Answer 22

highest water potential
it decreases/ becomes more negative

Question 23

what is isotonic?

Answer 23

two solutions having the same water potential

Question 24

what is hypertonic?

Answer 24

total molecular conc of dissolved solute particles is greater than that of another cell

Question 25

what is hypotonic?

Answer 25

total molecular conc of dissolved solute particles is less than that of another solution

Question 26

what does the rate of osmosis depend on?

Answer 26

water potential gradient- higher means faster
thickness of exchange surface- thinner means faster
surface area- larger means faster

Question 27

what happens to a cell in a hypotonic solution? what is turgor?

Answer 27

net movement is into cell so cells w/o walls lyse
plant cells have walls so prevent breaking- turgor pressure is pressure pushing against wall

haemolysis- rbc busrts

Question 28

what happens to cells in hypertonic solutions? what is plasmolysis?

Answer 28

water inside the cell flows out so cells lose water and cant divide/ function
plasmolysis is protosplast (everything in cell appart from wall) shrinking away from cell wall can be reversed
cells w/o cell walls shrink resulting in dehydrated cells can be reversed

Question 29

what is active transport?

Answer 29

movement of particles from an area of lower concentration to an area of higher concentration using energy

Question 30

similarity between facilitated diffusion and active transport

Answer 30

both use carrier proteins

Question 31

differences between active transport and facilitated diffusion

Answer 31

against/ down conc gradient
requires energy (ATP)/ doesn’t

Question 32

what are cotransporters?

Answer 32

type of carrier protein that binds 2 molecules at a time
the conc gradient of one is used to move other against its own conc gradient

Question 33

factors affecting rate of active transport

Answer 33

speed of individual carrier proteins
number of carrier proteins present
rate of respiration/ availability of ATP

Question 34

why does cotransport take place?

Answer 34

diffusion creates an equilibrium so not all available glucose/ amino acids would be able to pass out of body

Question 35

what is cotransport?

Answer 35

indirect active transport
glucose and amino acid molecules being drawn into cells with sodium ions

Question 36

describe the sodium-potassium pump

Answer 36

1) Na ions actively transport out of epithelial by sodium potassium pump (carrier protein)
2) maintains higher conc in lumen than the epithelial cells
3) Na ions diffuse into epithelial cell through carrier protein and carry glucose/ amino acids with them. Na diffuses, glucose/ amino acids go against conc gradient
4) glucose/ amino acids pass to blood plasma by facilitated diffusion using carrier proteins