Cell Membranes

Question 1

ways substances can move across membranes (3)

Answer 1

osmosis
active transport
diffusion

Question 2

cell surface/plasma membrane function (csm)

Answer 2

act as barrier between cell and enviro, controlling substances in + out cell
so are partially permeable

Question 3

partially permeable definition

Answer 3

it lets some molecules through but not all

Question 4

membranes inside cells function (3)

Answer 4

around organelles, dividing cell into different compartments
barrier between organelle + cytoplasm
control substances in + out organelle

Question 5

3 substances making up membrane

Answer 5

lipids (mainly phospholipids)
proteins
carbohydrates

Question 6

explain the fluid mosaic model

Answer 6

phospholipid bilayer - “fluid” as constantly moving
proteins scattered through bilayer
- carrier + channel allow large molecules + ions to pass through membrane
- receptor proteins
- some proteins fixed, others move sideways through bilayer
- glycoproteins (protein w carb attached)
- glycolipids
- cholesterol molecules

Question 7

phospholipids in cms

Answer 7

form barrier to dissolved substances
hydrophilic head
hydrophobic tail
bilayer formed when arrange themselves, head face out towards h2o
bilayer center is hydrophobic - no water soluble substances can pass through eg ions + polar molecules

Question 8

cholesterol function + where found

Answer 8

gives membrane stability

in all cell membranes but bacterial

Question 9

what cholesterol does

Answer 9

type of lipid
binds to phospholipid tails in bilayer so pack closer
restricts movement - cm is more rigid
helps maintain shape of cell / organelle
has hydrophobic regions - further barrier

Question 10

benefit of cholesterol in animal cells + blood cells

Answer 10

no cell wall, so helps maintain shape

Question 11

membranes at below 0*C

Answer 11

phospholipids dont have much E so dont move much + pack close -> rigid
channel + carrier denature -> ↑ permeability
ice crystals? pierce membrane - more permeable when thaw

Question 12

membranes at 0 - 45*C

Answer 12

phospholipids arent packed as close
partially permeable
as temp ↑ phospholipid movement ↑ since more E
- this ↑ permeability of membrane

Question 13

membranes at over 45*C

Answer 13

bilayer breaks down, cm ↑ permeability
h2o in cell expands -> pressure on cm
channel + carrier denature, ↑ permeability since can’t control in + out

Question 14

investigating cell membrane permeability practical 4

Answer 14

how temp affects beetroot membrane permeability

1. use scalpel to cut 5 equal pieces of beetroot + rinse them to remove pigment released in cutting
2. each piece in different test tube w 5cm^3 h2o
3. each tube in h2o bath at different temps for same length of time
4. remove pieces from tubes leaving coloured liquid
5. turn on colorimeter + let stabilise for 5 mins
6. pick blue colour filter (470 nm wavelength)
7. put distilled h2o in curvette 3/4 full. make sure class isnt frosted or scratched where light will be passing through. calibrate to zero
8. transfer some solution from test tube 1 to new curvette w pipette (3/4 full)
9. put in colorimeter and read and record absorbance
10. repeat 8 + 9
11. ↑er absorbance reading, more pigment released, so ↑er permeability of cm

Question 15

investigating effect of solvents practical

Answer 15

place pieces of beetroot in different solvents, eg alcohol

↑ conc of a solvent means ↑ permeability since it it dissolves the lipids in the membrane

Question 16

process of diffusion

Answer 16

net movement of particles down a conc gradient from an area of high to low conc, they can diffuse both ways though but net movement is to low conc
continues till particles evenly distributed

Question 17

factors affecting diffusion (3)

Answer 17

1. ↑er the conc gradient, faster rate of diffusion
   ROdiffusion slows over time until eqm reached
2. thinner exchange surface, less distance particles have to travel so quicker ROdiffusion
3. larger surface area, faster ROdiffusion

Question 18

factors affecting facilitated diffusion

Answer 18

1. ↑er conc gradient, faster ROdiffusion , but rate levels off as eqm reached
2. no. channel and carrier proteins, when all are in use, FD cant happen any faster, even if conc gradient was ↑

Question 19

what is a conc gradient

Answer 19

the path from low to high conc

Question 20

simple diffusion

Answer 20

when particles diffuse directly across a membrane

Question 21

why is facilitated diffusion needed

Answer 21

• larger molecules eg amino acids and glucose would diffuse slowly through phospholipid bilayer due to size,
• charged paritcles eg polar molecules and ions diffuse slowly cuz water soluble and hydrophobic center of bilayer

Question 22

is FD passive? ↑ or ↓ conc gradient?

Answer 22

↓ conc gradient

passive process

Question 23

2 proteins used in FD

Answer 23

carrier proteins

channel proteins

Question 24

carrier proteins

Answer 24

move large molecules

different proteins move different molecules

Question 25

how do carrier proteins work in FD

Answer 25

large molecule attaches to protein in membrane the protein then changes shape this releases molecule on other side of membrane

Question 26

channel proteins

Answer 26

form pores in membrane that charged particles diffuse through different proteins facilitate diffusion of different charged particles

Question 27

calculating ROdiffusion

Answer 27

find gradient of line on straight line graph on curve, draw tangent change y / change x add units

Question 28

what is osmosis

Answer 28

diffusion of h2o molecules across partially permeable membrane area of ↑er water potential to ↓er (eg more/less h2o molecules passive

Question 29

what is water potential

Answer 29

potential / likelihood of h2o molecules to diffuse in or out of solution more negative - stronger conc of solute in solution

Question 30

what wp is pure water

Answer 30

0 | decreases when solute added

Question 31

define isotonic

Answer 31

cells in isotonic solution won't lose / gain h2o | no net movement of h2o molecules since wps in cell outside and in the same

Question 32

define hypotonic solution

Answer 32

solution w ↑er wp than in cell

Question 33

define hypertonic solution

Answer 33

solution w ↓er wp than in cell

Question 34

what happens if cell is in hypotonic solution

Answer 34

cell will swell as h2o moves in by osmosis

Question 35

what happens if cell is in hypertonic solution

Answer 35

cell will shrink as h2o moves out by osmosis

Question 36

factors affecting ROosmosis

Answer 36

- bigger wp gradient, faster rate. rate ↓ over time as wp difference gets smaller - thinner exchange surface, faster rate - larger SA, faster rate

Question 37

active transport

Answer 37

movement of molecules/ions from low to high conc uses carrier proteins and co-transporters active process

Question 38

carrier proteins in AT

Answer 38

same as facilitated diffusion but moves molecules from low to high conc and requires E E usually from hydrolysis of ATP

Question 39

co transporters + example

Answer 39

type of carrier p bind 2 molecules at a time one molecule being transported down its conc gradient, which transports a different molecule against its own eg sodium and glucose co transporter

Question 40

factors affecting AT

Answer 40

- speed of individual carrier proteins - number of carrier proteins - ROphotosynthesis + availability of ATP, no respiration = no AT

Question 41

co transport and absorption of glucose

Answer 41

1. Na+ ATed out epithelial cells in ileum to blood by Na/K pump creating conc gradient as ↑er conc Na+ ions in lumen of ileum than inside cell 2. causes Na+ to diffuse from lumen of ileum to epithelial cells ↓ conc gradient via Na-glucoseco transporter conc of glucose in cell ↑ 3. glucose diffuses out cell to blood, ↓ conc gradient through channel protein

Question 42

investigating water potential 3 steps

Answer 42

1. make serial dilutions 2. measure change in mass 3. produce calibration curve

Question 43

what is a serial dilution

Answer 43

when you create a set of solutions that ↓ in conc by same factor each time useful when making weak solutions as dont have to measure out v small vols

Question 44

how to make a serial dilution

Answer 44

??

Question 45

how to measure change in mass

Answer 45

1. use cork borer to cut potatoes into identical chunks, 1cm diameter. put into groups of 3 and measure w balance 2. put a group into a solution and leave for 20 mins 3. take out of solution and pat dry gently w paper towel 4. repeat w each group 5. calc % change in mass for each group

Question 46

how to produce calibration curve

Answer 46

use results of % mass change and plot graph against conc of solution determine wp by looking at where it crosses at 0