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Biology A level > 2.3 Membranes > Flashcards

2.3 Membranes Flashcards

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1
Q

What is the cell-surface made of?

A

lipids and proteins
phospholipid molecules

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2
Q

What do the phosphate heads contain?

A

glycerol and phosphate

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3
Q

what do the phospholipid tails (fatty acid tails) contain?

A

a long hydrocarbon chain of fatty acids

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4
Q

What is the role of a cell-surface membrane?

A

they surround cells and act as a barrier between the cell and its environment controlling which substances enter and leave the cell. They are selectively permeable = choses substances

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5
Q

What is the role of membranes around organelles?

A

the membranes around organelles divide the cell into different components and act as a barrier between the organelle and the cytoplasm

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6
Q

What is the problem with the cell-surface membran being small?

A

cannot see all the details of its structure even under an electron microscope

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7
Q

What is the fluid Mosaic model?

A

describes how the molecules of the different substances that make up the membrane are arranged in a mosaic and not all these molecules stay in place

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8
Q

How are phospholipid molecules arranged in the membrane?

A

in a bilayer

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9
Q

What are receptor proteins?

A

allow the cell to detect chemicals released from other cells. The chemicals signal to the cell to respond in some way.

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10
Q

What are glycoproteins?

A

proteins with a carbohydrate chain

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11
Q

What is a glycolipid?

A

lipid with a carbohydrate chain

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12
Q

What are the functions of membrane proteins?

A

may act as enzymes
may act as channels
act as carrier proteins
act as receptors for hormones
act as molecules that are important in cell recognition

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13
Q

What is the role of cholesterol in the membrane?

A

adds strength and prevents the movement of other molecules in the membrane
helps maintain the shape of animal cells - important for cell that aren’t supported by other cells (red blood cells)
prevents the movement of other molecules in the membrane
prevents bursting
controls membrane fluidity

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14
Q

How does cholesterol make the membrane less fluid?

A

it fits between the phosopholipids and binds to the hydrophobic tails = causes them to pack more closely together
this retricts the movement of phospholipids making the membrane more rigid = less fluid

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15
Q

Why doesnt the membrane allow water soluble substances through?

A

the centre of the bilayer is hydrophobic and it acts as a barrier to these dissolved substances

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16
Q

What practical is used to test the permeability of the membrane?

A

Beetroot cells:
1. 10 test tubes, x5 labelled A, x5 labelled B and assign each test tube a temp (30,40,50,60,70)
2. 5cm3 of distilled water in A test tubes
3. place each A test tube in appropriate thermostatically controlled water bath for 5 mins
4. add 3 beetroot discs to test tube A and start timer
5. leave in water bath for 2 mins then put a bung in and invert the test tube x10
6. pour the liquid only into corresponding test tube B for that temp
9. take 5 test tubes to a colorimeter
10. staring with lowest temp B test tube, place test tube in colorimeter and take the reading of % absorption = press T on colorimeter

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17
Q

What are the surfaces where diffusion takes place called?

A

exchange surfaces

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18
Q

What is the rate of diffusion?

A

the amount diffused through the surface / the time taken

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19
Q

What are the factors affecting diffusion rate?

A

temperature (increase KE) - higher = faster diff.
surface area (microvilli) - larger = faster diff.
difference in concentration (concentration gradient) - higher = faster diff.
diffusion distance - thinner = faster diff.
lipid solubility - higher = increased diff
membrane fluidity - more fluid = increased diff

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20
Q

What is simple diffusion?

A

molecules diffusing directly through a cell membrane

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21
Q

What type of molecules do carrier proteins diffuse?

A

large, water-soluble molecules

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22
Q

Why do charged and water-soluble molecules diffuse slowly through the membrane?

A

the centre of the bilayer is hydrophobic

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23
Q

How do carrier proteins facilitate diffusion?

A

differenr carrier proteins facilitate the diffusion of different molecules:
1. molecule attaches to a carrier protein on the carrier’s binding site which is specific to the molecule
2. the protein changes shape when they bind to the molecule
3. this releases the molecules on the opposite side of the membrane

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24
Q

How do channel proteins carry out facilt. diffusion?

A

forms pores in the membrane for charged particles to diffuse through
1. gates open for ions to pass through according to the needs of the cell = pore formed
2. ions pass through the channel

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25
Why does the conc. gradient affect the rate of diffusion?
the higher the conc.gradient, the faster the rate of diffusion as diffusion takes place, the difference in conc. decreases until it reaches an equilibrium, diffusion slows down over time
26
What factors affects facilitated diffusion?
conc.gradient - higher = faster diff. no. of channel and carrier proteins - more = faster diff.
27
How do you calculate the rate of diffusion from a graph?
the gradient
28
How is water potential formed?
water molecules are in constant motion and move randomly some will hit the membrane = collison creates pressue - water potential
29
What are the units for water potential?
units for pressure - KPa
30
What increases water potential?
the more water molecules that are presnt and can move about freely, the greater the water potential
31
What substance has the highest water potential?
water - 0KPa all other solutions will have a negative water potential
32
Why is the water potential higher outside of the cell than inside it?
there is net movement of water molecules from distilled water into the cell
33
What is osmosis?
the diffusion of water molecules across a selectively permeable membrane from an area of higher water potential to an area of lower water potential
34
What is water potential?
the liklelihood of water molecules to diffuse out or into a solution/ cell
35
What are the factors affecting osmosis?
water potential gradient - higher = faster rate thickness of exchange surface - thinner = faster rate surface area - larger = faster rate
36
What proteins are involved in Active Transport?
carrier = Co-transporters
37
What are the factors affecting Active Transport?
the speed of induvidual carrier proteins - faster =faster rate no. of carrier proteins - more = faster rate rate of respiration in the cell and availablity of ATP
38
What makes up the membrane?
Intrinsic proteins - channel and carrier proteins = spans the entire bilayer extrinsic proteins glycoprotein glycolipid cholesterol phospholipids surface proteins
39
What is the role of the glycoprotein in the membrane?
enables cells to recognise another cell as familiar or foreign allows WBC to move around the body and initiate immune repsonses and identifys other cells
40
What is the role of the glycolipids in the membrane?
act as recognition sites and antigens
41
What is the role of an extrinsic protein in the membrane?
mechanical support, it is connected to carbohydrate chains to make glycoproteins
42
What is the role of a surface protein in the membrane?
provides effective communication between the cell and its environment
43
What is a micelle?
the structure that phospholipids on the surface of the water it forms a monolayer - hydrophyllic head on the outside, hydrophobic tails in the centre and forms a circle it helps the body absorb lipid and fat soluble vitamins
44
What are the qualities of the phosphate head?
hydrophyllic polar contains glycerol and phosphate
45
What does hydrophyllic mean?
attracted to water
46
What are the qualities of the fatty acid tails of a phospholipid?
non-polar hydrophobic contains long hydrocarbon chains and fatty acids
47
What determines the allignment of the phospholipids?
the way they react with water
48
How is a barrier formed with the phospholipids?
the centre of the bilayer is hydrophobic which doesnt allow water soluble substances through it and acts as a barrier to these dissolved substances
49
What is the role of a channel protein?
facilitated diffusion of ions
50
What is a uniport?
transports 1 specific ion/ molecule down a conc.gradient (positive diffusion)
51
What are the two types of Co-transport?
symport and antiport
52
What is symport?
two different substances transported simultaneously at the same time in the same direction
53
What is antiport?
transports two different substances in opposite directions at the same time
54
Why do intrinsic proteins in the membrane have a hydrophyllic lining?
the tails create hydrophobic area which polar (water-soluble) molecules cant pass through
55
What are the effects temperatures below 0'C on the permeablility of the membrane?
phospholipids are packed closely together and the membrane is rigid. But channel and carrier proteins deform, increasing the permeability
56
What are the effects temperatures between 0'C and 45'C on the permeablility of the membrane?
the phospholipids can move around and aren't packed as tightly together = the membrane is partially permeable as the temp increases the phospholipids move around more as they have more energy = increases permeablilty
57
What are the effects temperatures above 45'C on the permeablility of the membrane?
the phospholipid bilayer starts to break down and the membrane becomes more permeable Channel and carrier proteins start to deform so they cant control what enters/ leaves the cell = increases permeablilty.
58
What is the relationship between cholesterol and the membranes fluidity?
increase in cholesterol = decrease in membrane fluidity
59
What does a reduce in fluidity cause?
the membrane can no longer contain the contents of the cell
60
How does cholesterol make the membrane more rigid?
it binds to the hydrophobic tails which causes them to pack more closely together restricting the movement of the phospholipids
61
Where does simple diffusion take place in the membrane?
molecules pass through the phospholipid bilayer and the molecules pass between the phospholipids
62
What are the qualities of substances of simple diffusion in the membrane?
small non-polar lipid soluble eg: Oxyegn, gases, carbon dioxide gas exchange
63
How do molecules pass through the membrane by facilitated diffusion?
through a protein Ions travel through a channel protein molecules travel through a carrier protein
64
What are the qualities of molecules that dissuse by facilitated diffusion in the membrane?
polar (ions) water soluble large eg. glucose, amino acids, ions
65
What is the relationship of the rate and conc.gradient of simple diffusion?
as the conc.grad increases the rate of diffusion increases
66
What is the relationship of the rate and conc.gradient of facilitated diffusion?
intially, as the conc, grad increases the rate of diffusion increases then over time, the conc,grad increases, the rate of diffusion become constant as the no. and availablility of transport proteins becomes a limiting factor
67
Why do we start with a temp of 30'C for the beetroot prac?
a beetroots normal temp is 25'C underground
68
What is the definition of diffusion?
the net movement of molecules/ions down a conc.gradient until an equililbrium is reached. It is a passive process
69
Why are beetroot cells used to investigate the permeablility of the membrane?
beetroot cells contain a purple dye called anthocyanin which can diffuse across the beetrtoot membrane via the channel proteins
70
What are 3 variables that need to be controlled in the beetroot prac?
the volume of water in the test tubes the length of the beetroot time for diffusion to take place
71
Why must the beetroot cylinders need to be rinsed fully?
it removes pigment off the side of the beetroot it removes excess pigment was leaked when it was cut so the results are from diffusion
72
What is the effect of increasing temp on the permeablility of cell membranes?
increase temperature = increases kinetic energy of the phospholipids and proteins. phospholipid will move move = membrane becomes more fluid. Increased KE of the pigment = results in increased diffusion rate denatures the carrier proteins ans pigment leaks out of the membrane, uncontrollably
73
What is Active Transport?
the movement of a substance from a low conc. to a high conc using metabollic energy and a carrier protein
74
What is the process of Active Transport?
1. transport through carrier proteins 2. molecule binds to a receptor complementary in shape on the protein 3. ATP used 4. this causes the protein to change shape and release the molecule to the other side
75
What is the process of co-transport in the ileum?
1. carrier proteins enable sodium ions to be actively transported from the epithelial cell into the blood in the capillary = reduces sodium ion conc. in epithelial cell compared the lumen in the ileum 2. sodium ions diffuse from the lumen of the ileum into the epithelial cell - facilt.diff 3. the protein the sodium ions diffuse through is a co-transport protein = glucose/amino acids also attach and are transported into the epithelial cell against their conc,grad 4. glucose moves by facilit,diff from the epithelial cell into the blood
76
How is the epithelial cell adapted for co-transport?
microvilli: increases S.A for co-transport proteins it is a folded membrane with lots of carrier proteins embedded in the membrane for max apsorbsion of glucose
77
Why is the conc. of glucose in the blood lower then in the epithelial cells?
the blood flows and carries away absorbed glucose maintaining a conc.grad of glucose between epithelial cell and capillary
78
What limits Active transport?
anything that limits aerobic respiration = oxygen availability, respiratory inhibitant (cyanide) the number and availability of carrier proteins
79
Why does more active transport happen in a higher tempreture?
the ions have more kinetic energy so they are more likely to collide with carrier proteins
80
How does a respiratory inhibitant decrease the rate of Active transport?
inhibits repiration = reduces the energy produced by aerobic respiration
81
What does a plato on a graph show for transporting molecules?
an equilibrium has been reached = facilt.diff only
82
what causes water potential to lower?
adding solutes to water forming a solution
83
What are free water molecules?
water molecules in a solution that are not surrounding a solute molecule
84
What is the method of the potato prac for osmosis?
1. use a cork boere to cut potato dics into identically sized cylinder = 1cm in diameter 2. divide potatos in groups of 3 and measure the mass of each group using a mass balance 3. place one group into each sucrose solution 4. leave potatos in solution for about 20 mins (should all have the same amount of time for osmosis) 5. remove and blot potatoes with paper towel= removes excess water 6. weigh each group again and record results 7. calulate % change in mass for each group 8. use results to draw a calibration curve
85
What are the potato prac findings?
potato chips will gain water (therefore mass) in solutions with a higher water potential than the chips and lose water in solutions witha lower water potential
86
What does isotonic mean?
the water potential of the external solution is the same as the cell no net movement of water molecules no change in size of the cell
87
What does hypertonic mean?
the water potential of external solution is lower than in the cell
88
What does hypotonic mean?
the water potential of the external solution is higher than the cell
89
What happens to a plant cell in a hypetonic solution?
water diffuses out by osmosis = cell shrinks, shrivels and dies cell becomes plamolysed = the cell membrane pulls away from the cell wall
90
What happens to a plant cell in a hypotonic solution?
the cytoplasm swells and expands until it bursts the cell becomes turgid as water enters the cell by osmosis
91
What happens to animal cells in a hypertonic solution? (rbc)
cytoplasm shrinks = water leaves cell by osmosis crenation
92
What happens to a animal cell (rbc) in a hypotonic solution?
water enters the cell by osmosis - cell swells and expands until it bursts cell lysis = cell burts - no cell wall
93
What is the diluting from a stock solution equation?
C1 X V1 = C2 X V2 c = concentration v = volume 1 = original/ stock solution 2 = solution we want to make
94
What are the precautions of the potato prac?
use the same potato the time the cylinders were left in the solution should be the same potato discs need to be blotted before weighed tempreture of solutions should be the same potato should be fully semerged = osmosis SA should be the same make sure there was no skins on the potatoes = has different permeablility to water - would alter results
95
How would you make the potato prac more accurate?
have smaller intervals of sucrose solution conc
96
Why will a droplet of sucrose solution move up in another sucrose solution with different concentrations?
the drop is less dense than the solution so the conc of the drop is less than the solution - it is more dilute as water moved out of the cell into the droplet solution so the water potential of the droplet solution is higher than in the cell so the droplet solution is hypertonic to the cell
97
Why will a droplet of sucrose solution move down in another sucrose solution with different concentrations?
the droplet is more dense than the solution the concentration of the drop is higher than the conc of the solution - less dilute water moved into the cell by osmosis so the water potential of the droplet solution is hypotonic to the cell
98
What is endocytosis?
the process by which cells take in substances from outside of the cell by engulfing them in a vesicle (endosome) active process
99
What happens if endocytosis happens repeatedly?
the cell size decreases because the membrane surface area decreases
100
What is exocytosis?
the process by which materials are removed from, or transported out of cells active process
101
How can the water potential of a cell/tissue be determined?
place into a dilution series of different concentrations, compare the changes in mass, plot a graph and where the line crosses the x axis is the water potential of the cell/tissue
102
How is the bilayer formed of the membrane?
the phospholipid heads are hydrophyllic so they attract water around them and the tails are hydrophobic so they repell water
103
Why would the cell-surface membrane appear as two dark lines under a microscope?
Membrane has phospholipid bilayer  Stain binds to phosphate / glycerol  On inside and outside of membrane 
104
Describe binary fission in bacteria
Replication of circular DNA  Replication of plasmids  Division of cytoplasm to produce 2 daughter cells 
105
What happens when acid is added to a membrane?
the acid denatures the membrane proteins
106
What happens when you add an organic solvent to a membrane?
phospholipids dissolve
107
how may cell-surface membranes be adapted for rapid transport?
folded = large surface area large no. of protein channels for facilitated diffusiom large no. of protein carriers for active transport

Biology A level (36 decks)

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