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AQA A Level Biology > Cell Membranes > Flashcards

Cell Membranes Flashcards

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1
Q

ways substances can move across membranes (3)

A

osmosis
active transport
diffusion

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2
Q

cell surface/plasma membrane function (csm)

A

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

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3
Q

partially permeable definition

A

it lets some molecules through but not all

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4
Q

membranes inside cells function (3)

A

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

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5
Q

3 substances making up membrane

A

lipids (mainly phospholipids)
proteins
carbohydrates

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6
Q

explain the fluid mosaic model

A

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

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7
Q

phospholipids in cms

A

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

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8
Q

cholesterol function + where found

A

gives membrane stability

in all cell membranes but bacterial

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9
Q

what cholesterol does

A

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

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10
Q

benefit of cholesterol in animal cells + blood cells

A

no cell wall, so helps maintain shape

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11
Q

membranes at below 0*C

A

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

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12
Q

membranes at 0 - 45*C

A

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

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13
Q

membranes at over 45*C

A

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

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14
Q

investigating cell membrane permeability practical 4

A

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
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15
Q

investigating effect of solvents practical

A

place pieces of beetroot in different solvents, eg alcohol

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

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16
Q

process of diffusion

A

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

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17
Q

factors affecting diffusion (3)

A
  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
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18
Q

factors affecting facilitated diffusion

A
  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 ↑
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19
Q

what is a conc gradient

A

the path from low to high conc

20
Q

simple diffusion

A

when particles diffuse directly across a membrane

21
Q

why is facilitated diffusion needed

A
  • 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
22
Q

is FD passive? ↑ or ↓ conc gradient?

A

↓ conc gradient

passive process

23
Q

2 proteins used in FD

A

carrier proteins

channel proteins

24
Q

carrier proteins

A

move large molecules

different proteins move different molecules

25
Q

how do carrier proteins work in FD

A

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

26
Q

channel proteins

A

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

27
Q

calculating ROdiffusion

A

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

28
Q

what is osmosis

A

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

29
Q

what is water potential

A

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

30
Q

what wp is pure water

A

0

decreases when solute added

31
Q

define isotonic

A

cells in isotonic solution won’t lose / gain h2o

no net movement of h2o molecules since wps in cell outside and in the same

32
Q

define hypotonic solution

A

solution w ↑er wp than in cell

33
Q

define hypertonic solution

A

solution w ↓er wp than in cell

34
Q

what happens if cell is in hypotonic solution

A

cell will swell as h2o moves in by osmosis

35
Q

what happens if cell is in hypertonic solution

A

cell will shrink as h2o moves out by osmosis

36
Q

factors affecting ROosmosis

A
  • bigger wp gradient, faster rate. rate ↓ over time as wp difference gets smaller
  • thinner exchange surface, faster rate
  • larger SA, faster rate
37
Q

active transport

A

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

38
Q

carrier proteins in AT

A

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

39
Q

co transporters + example

A

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

40
Q

factors affecting AT

A
  • speed of individual carrier proteins
  • number of carrier proteins
  • ROphotosynthesis + availability of ATP, no respiration = no AT
41
Q

co transport and absorption of glucose

A
  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
42
Q

investigating water potential 3 steps

A
  1. make serial dilutions
  2. measure change in mass
  3. produce calibration curve
43
Q

what is a serial dilution

A

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

44
Q

how to make a serial dilution

A

??

45
Q

how to measure change in mass

A
  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
46
Q

how to produce calibration curve

A

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

AQA A Level Biology (4 decks)

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