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2b cell membranes Flashcards

1
Q

role of membranes

A

control what passes through them

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2
Q

what are all cells surrounded by

A

membranes

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3
Q

what are many organelles surrounded by

A

membranes

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4
Q

cell surface membranes

A

surround cells. they are a barrier between the cell and its environment controlling which substances enter and leave the cell. they are partially permeable, substances can move across via diffusion osmosis or active transport

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5
Q

membranes around organelles

A

divide the cell into different compartments - act as a barrier between the organelle and the cytoplasm. they are also partially permeable and control which substances enter and leave the organelle

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6
Q

basic structure of cell membranes

A

composed of lipids (mainly phospholipids), proteins, and carbohydrates

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7
Q

fluid mosaic model

A

1972
- describes the arrangement of molecules in the membrane

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8
Q

what do phospholipid molecules form

A

a continuous double layer, phospholipid bilayer

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9
Q

why is the bilayer fluid

A

becasue the phospholipids are constantly moving

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10
Q

what is present within the bilayer

A

cholesterol molecules

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11
Q

what is scattered through the bilayer

A

proteins, like tiles in a mosaic. including channel proteins and carrier proteins which allow large molecules and ions to pass through the membrane.

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12
Q

receptor proteins

A

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

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13
Q

proteins in the bilayer

A

some able to move sideways while others are fixed in position

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14
Q

what do some proteins in the bilayer have

A

a polysaccharide chain attatched - these are called glycoproteins

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15
Q

what do some lipids in the bilayer have

A

a polysaccharide chain attached - these are called glycolipids

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16
Q

what do different compartments of the cell membrane have

A

different roles

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17
Q

what do phospholipids molecules have

A

a head and a tail

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18
Q

phosopholipid head

A

hydrophilic - attracts water

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19
Q

phospholipid tail

A

hydrophobic - repels waer

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20
Q

how do the phospholipid molecules arrange themselves

A

automatically into a bilayer with the heads facing out towards the water on either side of the membrane

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21
Q

what is the centre of the bilayer

A

hydrophobic so the membrane doesnt allow water-soluble substances (like ions) through it - it acts as a barrier to these substances.

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22
Q

cholesterol

A

type of lipid

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23
Q

where is cholesterol presennt

A

in all cell membranes except bacterial cell membranes

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24
Q

where do cholesterol molecules fit

A

between the phospholipids. they bind to the hydrophobic tails of the phospholipids causing them to pack more closely togehter restricting the movement of the phospholipids, making the membrane less fluid and more rigid.

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25
what does cholesterol help to do
maintain the shape of animal cells. important for cells that arent supported by other cells
26
what effects the permeability of cell membranes
temperature, concentration. etc
27
what do beetroot cells contain
a coloured pigment that leaks out - the higher the permeability of the membrane the more pigment leaks out
28
how would you investigate how temperature affects beetroot membrane permeability
1. use a scalpel to carefully cut 5 equal sized pieces of beetroot. rinse the pieces to remove any pigment released during cutting 2. add the five pieces to five different test tubes each containing 5cm^3 of water 3. place each test tube in a water bath at a different temperature. 4. remove the pieces of beetroot from the tubes, leaving just thee coloured liquid 5. use a colorimeter to measure how much light is absorbed - the higher the absorbance the more pigment released so the higher the permeability of the membrane
29
how does temperature affect membrane permeability
higher temperatures means higher membrane permeability
30
what happens below 0 degrees
the phospholipids dont have much energy so cant move very much. the membrane is rigid but channel proteins and carrier proteins deform increasing the permeability of the membrane, ice crystals may form and pierce the membrane making it highly permeable when it thaws
31
what happens at temperatures between 0 and 45 degrees
the phospholipids can move and arent packed as tightly together - the membrane is partially permeable. as the temp increases the molecules move because they have more energy increasing the permeability of the membrane
32
what happens at temperatures above 45 degrees
the bilayer starts to melt and the membrane becomes more permeable. water inside the cell expands putting pressure on the membrane. channel and carrier proteins deform so they cant control what enters or leaves the cell increasing the membrane permeability.
33
diffusion
the net movement of particles from an area of high concentration to an area of lower concentration
34
concentration gradient
the path from an area of higher concentration to an area of lower concentration - particles diffusion down a concentration gradient
35
what kind of process is diffusion
a passive process
36
passive process
no energy is needed for it to happen
37
when can particles diffuse across cell membranes
when they can move freely through the membrane e.g. oxygen and carbon dioxide (small and non-polar)
38
simple diffusion
when molecules diffuse directly through a cell membrane
39
what does facilitated diffusion use
carrier and channel proteins
40
why would larger molecules diffuse slowly
because they are so big
41
why would charged particles diffuse slowly
they are water soluble and the centre of the bilayer is hydrophobic
42
what is used to diffuse large and charged molecules through the cell membrane
carrier and channel proteins
43
how does fascilitated diffusion move particles
down a concentration gradient, high concentration to a lower concentration
44
what kind of process is facilitated diffusion
passive process
45
how do carrier proteins move large molecules
1. a large molecule attaches to a carrier protein in the membrane 2. then the protein changes shape 3. this releases the molecule on the opposite side of the membrane
46
how do channel proteins move charged molecules
they form pores in the membrane allowing charged particles to diffuse through. different proteins facilitate the diffusion of different charged particles
47
what affects the rate of simple diffusion
- concentration gradient - thickness of the exchange surface - surface area
48
effect of concentration gradient on simple diffusion
the higher it is the faster the rate of diffusion, the difference in concentration between the two sides of the membrane decreases until it reaches an equilibrium. this means diffusion slows down over time.
49
effect of thickness of exchange surface on simple diffusion
the thinner the exchange surface the faster the rate of diffusion
50
effect of the surface area on simple diffusion
the larger the surface area the faster the rate of diffusion
51
factors affecting the rate of facilitated diffusion
- concentration gradient - number of chanell or carrier proteins
52
effect of concentration gradient on facilitated diffusion
the higher the conc. gradient, the faster the rat eof facilitated diffusion. as equilibrium is reached, the rate of facilitated diffusion will level off
53
effect of no. of channel and carrier proteins on facilitated diffusion
once all the proteins are in use, facilitated diffusion cannot happen any faster, even if you increase the conc. gradient. so the greater the number of channel or carrier proteins in the cell membrane. the faster the rate of facilitated diffusion.
54
osmosis
the diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of low water potential
55
water potential
the potential of water molecules to diffuse out of or into a solution
56
pure water
has the highest water potential
57
isotonic
when two solutions have the same water potential
58
what factors does the rate of osmosis depend on
- water potential gradient - thickness of exchange surface -surface area of exchange surface
59
effect of water potential gradient on osmosis
the higher the water potential gradient the faster the rate of osmosis. as osmosis takes place the difference in water potential on either side of the membrane decreases, so the rate of osmosis levels off over time
60
effect of thickness of exchange surface on osmosis
the thinner the exchange surface the faster the rate of osmosis
61
effect of surface area on osmosis
the larger the surface area the faster the rate of osmosis
62
serial dillution steps
1. line up five test tubes in a rack 2. add 10cm of the initial 2M sucrose solution to the first test tube and add 5cm of distilled water to the other four test tubes 3. using a pipette, draw 5cm of the solution from the first tube add it to the distilled water in the second test tube and mix throroughly 4. repeat the process to create different concentrations
63
how to find water potential of potatoes required practical method
1. use a cork borer to cut potatoes into identically sized chips 2. divide the chips into groups of three and measure mass using a scale 3. place one group into each of your sucrose solutions 5. leave the chips in the solutions for atleast 20 minutes 5. remove the chips, pat dry gently with a paper towel 6. weigh each group again and record results 7. calculate percentage change in mass for each group 8. use the results to make a calibration curve
64
when will the potato gain water
in solutions with higher water potential then their own
65
when will the potato lose water
in solutions with lower water potential then their own
66
where on the graph would you find the water potential of the potato
where it crosses the x axis
67
active transport
uses energy to move molecules and ions across membranes usually against a concentration gradient
68
how are carrier proteins used in active transport
a molecule attatches to the carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side
69
two main differences between active transport and facillitated diffusion
1. active transport moves from low - high concentration - facilitated diffusion moves from high - low concentration 2. active transport requires energy (ATP) whilst facillitated diffusion doesnt.
70
ATP
common source of energy in the cell
71
how is ATP produced
by respiration
72
what does ATP undergo
a hydrolysis reaction, splitting into ADP and P, releasing energy so that solutes can be transported
73
cotransporters
a type of carrier protein
74
what does a cotransporter do
1. bind two molecules at a time 2. the conc. gradient of one of the molecules is used to move the other molecule against its own conc. gradient.
75
what factors effect the rate of active transport
- speed of individual carrier proteins - the number of carrier proteins present - rate of respiration and availability of ATP
76
effect of speed of individual carrier proteins on active transport
the faster they work the faster the rate of active transport
77
effect of the number of carrier proteins present on active transport
the more proteins there are, the faster the rate of active transport
78
effect of the rate of repsiration and availability of ATP on active transport
if respiration is inhibited, active transport cant take place
79
how is glucose absorbed
by co transport
80
where is glucose absorbed to
the bloodstream in the small intestine
81
ileum
the final part of the small intestine
82
glucose ileum
the conc. of glucose is too low for it to diffuse out into the blood. so glucose is absorbed from the lumen by cotransport
83
how does glucose get absorbed into the bloodstream
1. sodium ions are actively transported out of the epithelial cells, into the blood by a sodium potassium pump. this creates a conc. gradient. there is now a higher conc. of sodium ions in the lumen of the ileum than inside the cell 2. this causes sodium ions to diffuse from the lumen into the epithelial cell, down the concentration gradient. they do this via sodium- glucose co transporter proteins 3. the co-transporter carrier glucose into the cell with the sodium. as a result the conc. of glucose inside the cell increases 4. glucose diffuses out of the cell, into the blood down its conc. gradient through a protein channel, by facilitated diffusion

biology (6 decks)

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