2B- Cell Membrane

Question 1

what do membranes control

Answer 1

what passes through as they are partially permeable

Question 2

what types of diffusion does cell membranes let happen

Answer 2

diffusion, osmosis and active transport

Question 3

what are the jobs of the membrane

Answer 3

provide a barrier between enviroment and the inside
divide the cell into different compartments
controls what enter and leaves the cell

Question 4

what is the fluid mosiac model

Answer 4

a model that suggested the arrangement of molecules in the membrane are phosopholipd molecules that form a bilayer.

Question 5

why is it desribed as a fluid

Answer 5

the phosopholipids are constantly moving

Question 6

why is it described as mosiac

Answer 6

proteins are scattered through the bilayer.
e.g the channel proteins and receptor proteins

Question 7

what are the two parts of a phospholipid in the membrane

Answer 7

hydrophilic head- attracts water
hydrophobic tail - repels water

Question 8

how does the phospholipid bilayer work

Answer 8

the heads face out towards the water/ enviroment
the tails face in
this is so the membrane doesnt allow water soluble substances though it

Question 9

what does cholestrol do in the membrane

Answer 9

holds together each phospholipid so they are more tightly packed

Question 10

desribe an experiment that allows you to test the permeability of the mebrane

Answer 10

1) use a scalpel to cut five equally sized pieces of beetroot
2) add the five pieces of beetroot to 5 test tubes and add 5cm3 of water using a pipette
3) place each test tube in a water bath of different temperature e.g 10, 20, 30 etc for a set amount of time
4)remove pieces of beetroot from test tubes leaving the coloured liquid
5) use a colourimeter to measure the absorbance of the liquid
the higher the absorbance the more colour pigment so higher permeablility of membrane

Question 11

how does increasing temp increase membrane permeability

Answer 11

look in text book

Question 12

what is simple diffusion

Answer 12

net movement of particle from an area of higher concentration to an area of lower concentration

Question 13

what is the concentration gradient

Answer 13

the path from an area of higher concentration to an area of lower concentration

Question 14

what kind of process is diffusion

Answer 14

passive process - no energy

Question 15

what is the difference between simple diffusion and facilitated diffusion

Answer 15

facilitated diffusion uses carrier proteins and protein channels

Question 16

why is facilitated diffusion used

Answer 16

it can transport larger molecules and charged particles through more quickly

Question 17

how does a carrier protein work and what does it transport

Answer 17

it transport larger molecules

1) large molecule attaches to carrier protein
2) then the protein changes shape
3) this releases the molecule on the opposite side of the membrane

Question 18

how does a channel protein work and what does it transport

Answer 18

it transports channel proteins
through normal diffusion

Question 19

what does simple diffusion depend on

Answer 19

the concentration gradient
the thickness of the exchange surface
the surface area

Question 20

how does microvilli increase diffusion rate

Answer 20

it increases SA

Question 21

what does facilitated diffusion depend on

Answer 21

concentration gradient
number of channel or carrier proteins

Question 22

what is osmosis

Answer 22

the diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential

Question 23

what is water potential

Answer 23

the potential of water molecules to diffuse out of or into a solution

Question 24

what has the highest water potential

Answer 24

pure water

Question 25

what is it called when 2 solution have the same water potential

Answer 25

isotonic

Question 26

what does the rate of osmosis depend on

Answer 26

the water potential gradient the thickness of the exchange surface the surface area of the exchange surface

Question 27

desribe how to do serial dilution

Answer 27

1) line up 5 test tubes in a rack 2) add 10cm3 of intial 2M sucrose solution to first test tube and 5cm3 of water to the others 3) then using a pipette draw 5cm3 of solution from the first add it to the water in second tube and mix 4) now repeat this on the next test tubes but half the volume of 2M sucrose

Question 28

desribe the experiment to investigate the water potential of plant tissue

Answer 28

using the solutions you made 1) use a cork borer to cut potatoes into equally sized tubes 2) measure the mass of each of the potatoes 3) place one in each of your sucrose solutions 4) leave the chips in their for 20 minute 5) remove and gently pat dry then weigh the mass at end 6) work out the percentage change and draw a graph

Question 29

what is active transport

Answer 29

the process of moving molecules or ions across a cell membrane against a concentration gradient

Question 30

what 2 things make active transport different to facilitated diffusion

Answer 30

it goes from low to high it requires energy atp but it does use carrier proteins

Question 31

what is ATP and what happens to it in active transport

Answer 31

it is a common energy source it undergoes hydrolysis splitting it into ADP and Pi( inorganic phosphate) releasing energy

Question 32

what are cotransporters and how do they work

Answer 32

they are a type of carrier protein 1) they bind to 2 molecules at a time 2) the concentration gradient of one of the molecules is used to move the other molecules against its own conc gradient

Question 33

how does the sodium potassium pump work

Answer 33

=Binding of sodium ions: The pump protein binds to three sodium ions from the inside of the cell. =ATP hydrolysis: An ATP molecule binds to the pump and is broken down into ADP and a phosphate group, providing energy for the conformational change. Conformational change: =The pump changes shape, releasing the sodium ions to the outside of the cell. =Binding of potassium ions: The pump then binds to two potassium ions from the extracellular fluid. =Return to original shape: The pump returns to its original shape, releasing the potassium ions into the cell and completing the cycle.

Question 34

where does the sodium potassium pump work

Answer 34

in the small intestine in the illium