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OCR A LEVEL BIOLOGY > M2, C5 Plasma Membranes > Flashcards

M2, C5 Plasma Membranes Flashcards

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1
Q

what is compartmentalisation

A

the formation of separate membrane-bound areas in a cell

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2
Q

define plasma membrane

A

the cell surface membrane that separates the cell from its external envrionment

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3
Q

what are membranes formed from

A

a phospholipid bilayer
hydrophilic phosphate heads form the inner and outer surface of a membrane
fatty acid tails are sandwiched inside to form the hydrophobic core

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4
Q

where do cells normally exist

A

aqueous environments

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5
Q

why are phospholipid bilayers suited for aqueous environments

A

the outer surfaces of the hydrophilic phosphate heads can interact with water

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6
Q

what is the fluid-mosaic model

A

shows how proteins occupy various positions in the membrane
phospholipids are free to move within the layer relative to each other
this gives the membrane flexibility

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7
Q

what are the components in a cell membrane

A 
glycoprotein
glycolipid
cholesterol
hydrophilic heads of phospholipid molecules
extrinsic protein
pore
intrinsic protein
hydrophobic tails of phospholipid molecules
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8
Q

what are the 2 types of membrane proteins

A

intrinsic and extrinsic

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9
Q

what are intrinsic proteins

A

transmembrane proteins that are embedded in both layers of the membrane
have amino acids and hydrophobic R groups on the external surfaces which interact with the hydrophobic core keeping them in place

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10
Q

what are channel proteins

A

channel proteins - provide a hydrophilic channel to allow passive movement of polar molecules and ions down a concentration gradient. this is held in place by the interactions between the hydrophobic core and the R groups on the outside of proteins

they are intrinsic

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11
Q

what are glycoproteins

A

Proteins with carbohydrates attached

they play a role in cell adhesion (when cells join together) and act as receptors for chemical signals

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12
Q

what are glycolipids

A

phospholipids with carbohydrates attached

they are cell markers or antigens so the immune system recognises it as self or non-self

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13
Q

what is cell signalling

A

involves glycoproteins
when the chemical binds to the receptor on the glycoprotein, it elicits a response from the cell which can set off a cascade of events

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14
Q

what are extrinsic proteins

A

present in one side of the bilayer
have hydrophilic R groups on their outer surfaces
interact with polar heads of phospholipids or intrinsic proteins
some can move between layers

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15
Q

why is cholesterol in the plasma membrane

A

it regulates the fluidity of them
has a hydrophobic and hydrophilic end

they are positioned between the phospholipids in a membrane bilayer - the hydrophilic end interacts with the heads and the hydrophobic end interacts with the tails, pulling them together

therefore it adds stability but doesn’t make them too rigid - they stop the phospholipid molecules from grouping too closely and crystallising

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16
Q

what needs to happen for a chemical reaction to take place

A

all the organelles need to be in specific positions

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17
Q

what happens to phospholipids as temperature increases

A

they gain kinetic energy meaning they move more
the membrane becomes more fluid because it loses its structure
eventually they could break down completely

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18
Q

what does the loss of structure in cell membranes mean

A

they become more permeable meaning particles can more easily cross it

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19
Q

what happens to carrier and channel proteins as temp increases

A

denature

increases membrane permeability further

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20
Q

why is water essential for the formation of the phospholipid bilayer

A

Because the non-polar tails of the phospholipids are orientated away from water which forms a bilayer with the hydrophobic core
the charged phosphate heads interact with water which keeps it intact

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21
Q

what are carrier proteins

A

carrier proteins - passive and active transport into cells. this often involves the proteins changing shape

they are intrinsic

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22
Q

how do organic solvents affect membranes

A

they dissolve membranes which disrupts cells

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23
Q

give a common example of an organic solvent

A

alcohol

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24
Q

why is alcohol in anti-septic wipes

A

the alcohols dissolve the membranes of bacteria in a wound, killing them and reducing the risk of infection

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25
Q

why are pure or very strong alcohol solutions dangerous

A

they are toxic
they destroy cells
the molecules can enter the membranes and disrupt the membrane because they lie between phospholipids

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26
Q

what happens when a membrane is disrupted

A

it becomes more fluid and more permeable

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27
Q

give an example of a cell that needs intact cell membranes to function

A

nerve cells
if neuronal membranes are disrupted then nerve impulses are no longer transmitted as normal, hence why people behave differently when they drink alcohol

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28
Q

suggest an experiment to investigate how temperature affects membrane permeability

A
  1. get 5 small pieces of beetroot, all equal sizes
  2. thoroughly wash under water
  3. place in 100ml of distilled water in a water bath
  4. increase the water bath by 10 degrees
  5. samples of water taken 5 mins after the water bath has increased by 10 degrees
  6. measure the absorbance of each sample using a colorimeter with a blue filter
  7. repeat 3 times

the results show that absorbance rapidly increases after 50 degrees hence suggesting that the membrane is disrupted between 40 and 50 degrees

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29
Q

what microscope would you see a detailed plasma membrane

A

electron microscope - you would see the double line which is 7-10 nm thick

(a light microscope you would see a single line)

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30
Q

how can polar and non-polar molecules pass through the membrane

A

Polar molecules require proteins to enable them to pass through the membrane

Non-polar molecules can diffuse directly through the phospholipid bilayer

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31
Q

define diffusion

A

the net movement of particles from a region of higher concentration to a region of lower concentration

32
Q

when does diffusion continue to

A

until there is a concentration equilibrium between the 2 areas

33
Q

why does diffusion happen

A

particles in a gas or liquid have kinetic energy

this movement is random and unequal

34
Q

what slows down the overall movement in diffusion

A

particles are constantly colliding with each other

this means diffusion over short distances are faster

35
Q

what factors affect the rate of diffusion

A

temp - increases kinetic energy

concentration difference - overall movement will be larger

36
Q

what is simple diffusion

A

diffusion when there is no barrier/ membrane

37
Q

why are membranes described as partially permeable

A

polar molecules diffuse through a membrane at a slow rate

small polar molecules pass through more easily

38
Q

what is the rate at which molecules or ions diffuse across membranes is affected by

A

surface area

thickness

39
Q

what is facilitated diffusion

A

diffusion across a membrane through protein channels

40
Q

what are membranes with protein channels known as

A

selectively permeable

41
Q

what is the rate of facilitated diffusion dependent on

A 
temperature
concentration gradient
membrane surface area
thickness
number of channel proteins present
42
Q

what is active transport

A

the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration

43
Q

what is needed for active transport

A

metabolic energy is supplied by ATP

44
Q

what do carrier proteins act as in active transport

A

pumps

45
Q

give the process of active transport into the cell

A
  1. the molecule binds to receptors in the channel of the carrier protein on the ourside of the cell
  2. ATP binds to the carrier protein inside the cell and is hydrolysed into ADP and phosphate
  3. The binding of the phosphate molecule to the carrier protein causes the protein the change shape which opens up to the inside of the cell
  4. molecule is released to the inside of the cell
  5. phosphate molecule is released from the carrier protein and recombines with ADP to form ATP
  6. Carrier protein returns to its original shape
46
Q

why is active transport into the cell selective

A

because specific substances are transported by specific carrier proteins

47
Q

what is bulk transport

A

form of active transport
large molecules and whole cells are too large to move through channel or carrier proteins so are moved into and out of cell by bulk transport

48
Q

what are two types of bulk transport

A

endocytosis - bulk transport into cells

exocytosis - bulk transport out of cells

49
Q

what are the two types of endocytosis

A

phagocytosis - for solids

pinocytosis - for liquids

50
Q

give the process for endocytosis

A
  1. cell surface membrane invaginates when it comes into contact with material
  2. the membrane enfolds the material
  3. the membrane fuses which forms a vesicle
  4. vesicle pinches off and moves into cytoplasm to transfer material
51
Q

what are the basic steps for exocytosis

A

its the opposite of endocytosis
vesicles formed by the Golgi apparatus move towards and fuse with the cell surface membrane
the contents of the vesicle are then released outside of the cell

52
Q

why is ATP needed for bulk transport

A

the move vesicles along the cytoskeleton
change the shape of the cell to engulf materials
fusion of cell membranes as vesicles form or as they meet the cell surface membrane

53
Q

what is a solute

A

a substance dissolved in a solvent forming a solution

54
Q

what is water potential

A

the pressure exerted by water molecules as they collide with a membrane or container
it’s measured in pascals
symbol is the greek letter psi

55
Q

define pure water

A

has a water potential of 0kPa which is the highest possible value for water potential

56
Q

what happens when solutions with different concentrations/ different water potentials are separated by a partially permeable membrane

A

the water molecules can move between the solutions but solutes usually can’t

there is a net movement of water from the solution with high water potential to the solution with lower water potential

57
Q

is a solution more or less concentrated if the water potential is high

A

less

58
Q

what is hydrostatic pressure

A

the diffusion of water into a solution leads to an increase in volume of this solution
if the solution is in a closed system, pressure increases

59
Q

what are the units of hydrostatic pressure

A

kPa

60
Q

what happens if an animal cell is placed in a solution with a higher water potential than that of the cytoplasms

A

water will move into the cell by osmosis, increasing hydrostatic pressure inside the cell

61
Q

what is cytolysis

A

when the cell-surface membrane of an animal cell can’t stretch enough to withstand the hydrostatic pressure so breaks and the cell will burst

62
Q

what happens if an animal cell is placed in a solution that has a lower water potential than the cytoplasm

A

it will lose water to the solution by osmosis down the water potential gradient
causes a reduction in the cell volume and the cell-surface membrane ‘puckers’ (crenation)

63
Q

how is cytolysis or crenation prevented

A

animals have control mechanisms to make sure their cells are continuously surrounded by aqueous solutions with an equal water potential (isotonic)

64
Q

what is the aqueous solution in blood

A

blood plasma

65
Q

in a red blood cell, what happens if it is in a high water potential solution

A

water enters cell
it swells and bursts
haemoglobin is released

66
Q

in a red blood cell what happens if it is a low water potential solution

A

water leaves cell
haemoglobin is more concentrated so the cell appears darker
cell shrinks and shrivels

67
Q

in a red blood cell what happens if it is an equal water potential solution

A

water constantly enters and leaves at equal rates

red blood cell is normal

68
Q

where are solutes stored in a plant cell

A

dissolved in the vacuole

69
Q

what differs plants and animals in terms of osmosis

A

plants are unable to control water potential of fluid around them eg. roots are usually surrounded by almost pure water

70
Q

what happens when water enters a plant cell by osmosis

A

hydrostatic pressure increases
membrane is pushed against the rigid cell wall
the pressure against the cell wall is called turgor
as turgor increases it resists entry of further water and the cell is said to be turgid

71
Q

what is turgor pressure

A

pressure against the cell wall

72
Q

what is a cell called when it stops the entry of water into it

A

turgid

73
Q

what happens when plant cells are placed in a solution with a lower water potential

A

water is lost from the cells by osmosis

there is a reduction in the volume of the cytoplasm

74
Q

what does it mean when a cell is said to be plasmolysed

A

when water is lost from the cell through osmosis
if this doesn’t stop then volume of cytoplasm keeps reducing which pulls the cell-surface membrane away from the cell wall

75
Q

how can you investigate osmosis in plant cells

A

place pieces of potato or onion into sugar or salt solutions with different concentrations/different water potentials
water will move into or out of cells depending on water potential of the plant tissue
as the plant tissue gains or loses water it will increase or decrease in mass and size

76
Q

how can you investigate osmosis in animal cells

A

eggs are used
boil the egg, remove the shell and there is a single membrane bound structure
place the eggs in different concentrations of sugar syrup
overtime osmosis takes place and there will have been a net movement of water into or out of the eggs

77
Q

how thick is the plasma membrane

A

7-10nm

OCR A LEVEL BIOLOGY (23 decks)

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