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Bio Yr 12: Cell Structure > Cell Membranes & Transport > Flashcards

Cell Membranes & Transport Flashcards

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1
Q

What is the function of the cell surface membrane?

A
  • separates internal cell envi. from external envi
  • compartmentalises diff. structures (organelles) within cell
  • controls exchange of material across them [partially permeable]
  • acts as an interface for communication
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2
Q

What is the structure of the cell surface membrane?

A
  • phospholipid bilayer that contains proteins (intrinsic/integral or extrinsic/peripheral)
  • intrinsic = embedded in membrane
  • extrinsic = found on outer or inner surface of membrane
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3
Q

What is the structure of a phospholipid?

A
  • 1 hydrophilicphosphate head (polar so soluble in water)
  • 2 hydrophobic fatty acid tails (non-polar so insoluble in water)
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4
Q

What happens when phospholipids are shaken w water?

A
  • forms a micelle: sphere w hydrophilic heads facing out towards water + hydrophobic tails facing in towards each other
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5
Q

Why are cell membranes described as fluid mosaic?

A
  • fluid = phospholipids + proteins can move around via diffusion
  • mosaic = proteins within phospholipid bilayer produce a scattered pattern
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6
Q

What are the diff. types of molecules cell membranes contain?

A
  • lipids = phospholipids, cholesterol, glycolipids [also contains carbs]
  • proteins = glycoproteins [also contain carbs], transport proteins, enzymes
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7
Q

What is the structure of cholesterol?

A
  • hydrophobic tail + hydrophilic head
    • fit between phospholipid molecules + orientated same way
  • absent in prokaryotes membranes
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8
Q

What is the structure of glycolipids?

A
  • lipids w carbohydrate chains attached
  • carb chains project out into fluid surrounding cell
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9
Q

What is the structure of glycoproteins?

A
  • proteins w carbohydrate chains attached
  • carb chains project out into fluid surrounding cell
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10
Q

What are transmembrane proteins?

A
  • proteins that span the entire membrane
  • e.g. transport proteins
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11
Q

What is the function of phospholipids in cell surface membranes?

A
  • acts as a barrier to most water-soluble substances
    • so water-soluble molecules (e.g. sugars, AA + proteins) can’t leak out of cell + unwanted water-soluble molecules can’t get in
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12
Q

What is the function of cholesterol in the cell surface membrane?

A
  • regulates fluidity of membrane
  • sits between phospholipids: prevents them being compact when T°Cs are low = stops membrane freezing + fracturing
  • cholesterol + phospholipid tail interactions: stabilise cell membrane at higher T°Cs by stopping membrane becoming too fluid
  • contributes to impermeability of membrane to ions + inc. mechanical strength + stability of membranes
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13
Q

What is the function of glycolipids + glycoproteins in the cell surface membrane?

A
  • acts as receptor molecules due to carb chains on surface
    • allowing them to bind w substances at cell’s surface
  • some act as cell markers or antigens, for cell-to-cell recognition
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14
Q

What are the 3 main receptor types created from glycolipids + glycoproteins on the cell surface membrane?

A
  • signalling receptors for hormones + neurotransmitters
  • receptors involved in endocytosis
  • receptors involved in cell adhesion + stabilisation
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15
Q

What is the function of transport proteins in the cell surface membrane?

A
  • 2 types: channel + carrier proteins
  • create hydrophilic channels: allows ions + polar molecules to travel through membrane
  • each protein is specific to a particular ion or molecule
  • allows cell to control what substances enter or leave
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16
Q

What increases a membranes fluidity?

A
  • an inc. in unsaturated fatty acid chains: bc they are bent so are less tightly packed together so there’s less intermolecular forces
  • higher T°Cs: molecules have more energy so move more freely, inc. membrane fluidity
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17
Q

What is the definition of simple diffusion?

A
  • net movement of molecules or ions, down a conc. gradient, from an area of high conc. to an area of lower conc. until evenly distributed
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18
Q

What are the factors affecting the rate at which a substance diffuses across a membrane?

A
  • ‘steepness’ of conc. gradient
  • T°C
  • SA
  • properties of molecules or ions
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19
Q

How does the concentration gradient affect the rate of diffusion?

A
  • greater diff. in conc. = greater diff. in number of molecules passing in the 2 directions = faster rate
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20
Q

How does T°C affect the rate of diffusion?

A
  • higher T°Cs = particles have more KE = move faster so higher rate
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21
Q

How does surface area affect the rate of diffusion?

A
  • greater SA = greater number of particles crossing at any moment = faster rate
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22
Q

How does the properties of molecules or ions affect the rate of diffusion?

A
  • large molecules = slower rate bc require more energy
  • non-polar molecules = faster rate bc are soluble in the non-polar phospholipid bilayer
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23
Q

What is the definition of facilitated diffusion?

A
  • passive net movement of particles, down a conc. gradient, from an area of higher conc. to an area of lower conc. w the help of a transport protein
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24
Q

What are e.g.s of substances that can’t diffuse through the phospholipid bilayer of cell membranes?

A
  • large polar molecules (e.g. glucose + AA)
  • ions (e.g. sodium ions [Na+] + chloride ions [Cl-])
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25
Q

What are the 2 types of proteins that enable facilitated diffusion?

A
  • channel proteins
  • carrier proteins
26
Q

What are channel proteins?

A
  • water-filled pores
  • allow charged substances (e.g. ions) to diffuse through cell membrane
  • controls exchange of ions
  • fixed shape
27
Q

What are carrier proteins?

A
  • switches between 2 shapes
    • binding site open on one side of membrane, then opens on other side once shape switches
28
Q

What is the definition of osmosis?

A
  • movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane
29
Q

What is the water potential of pure water at atmospheric pressure?

A
  • 0kPa
30
Q

What happens if a plant cell is placed in pure water?

A
  • water enters plant cell through its partially permeable cell membrane by osmosis
  • bc pure water has a higher water potential than the plant cell
31
Q

What does a plant cell being described as turgid mean?

A
  • plant cell is fully inflated w water + has become rigid + firm
32
Q

What happens when a plant cell is placed in a solution w a lower water potential?

A
  • water leaves plant cell through its partially permeable cell membrane by osmosis
  • water leaves vacuole = protoplast shrinks + doesn’t exert pressure on cell wall
  • plant cell is plasmolysed
33
Q

What is the process plasmolysis?

A
  • when protoplast shrinks + begins to pull away from cell wall
  • only occurs in plant cells
34
Q

What happens when an animal cell is placed in a hypertonic solution [solution w a lower water potential]?

A
  • water leaves cell through its partially permeable cell membrane by osmosis + cell shrinks + shrivels up
35
Q

What happens when an animal cell is placed in a hypotonic solution (e.g. pure water) [solution w a higher water potential]?

A
  • water enters cell through its partially permeable cell membrane by osmosis + cell stretches until it bursts [cytolysis]
36
Q

What happens when an animal cell is placed in an isotonic environment?

A
  • no change to cell
  • bc solution inside + outside cell has the same solute conc.
37
Q

Describe a method used to investigate the water potential of a plant tissue?

A
  • use a cork borer to cut 5 potato cylinders (same length/mass) + blot them dry to remove excess moisture
  • measure + record initial mass then place into 10cm3 sucrose solutions of diff. water potentials
  • using a stopwatch leave cylinders in solution for 30 mins
  • then remove + dry them to remove excess liquid
  • finally measure + record final length + mass of each potato cylinder
  • calculate % change in mass for each potato cylinder
38
Q

How do you find the percentage change in mass of the potato cylinders?

A
  • (final mass - initial mass / initial mass) x100
39
Q

What do the results of the % change in mass of the potato cylinders indicate?

A
  • pos. % change = potato gained water by osmosis bc solution had higher water potential than potato
    • potato cells turgid
  • neg. % change = potato lost water by osmosis bc solution had lower water potential than potato
    • potato cells flaccid + may be plasmolysed
  • no % change = no overall net movement of water into or out of potato cells bc solution had same water potential as potato
40
Q

How do you find out the conc.of sucrose in the potato cylinders using a graph?

A
  • plot a graph for % change in mass (y) against conc. of sucrose (x)
  • where line of best fit crosses x axis = conc. of sucrose
41
Q

What are the diff. types of data you can have?

A
  • qualitative = non-numerical (e.g. blood group)
  • discrete = numerical that can only take certain values in a range (e.g. shoe size)
  • continuous = numerical that can take any value in a range (e.g. height or weight)
42
Q

What is the definition of active transport?

A
  • movement of molecules or ions into or out of a cell from an area of lower conc. to an area of higher conc. using ATP + carrier proteins
43
Q

Why does active transport require ATP?

A
  • ATP produced during respiration is hydrolysed to release energy
  • energy is used to make carrier protein change shape = to transfer particles across cell membrane
44
Q

What is active transport important in?

A
  • reabsorption of useful molecules + ions into blood after filtration into kidney tubules
  • absorption of some products of digestion from digestive tract
  • loading sugar from photosynthesising cells of leaves into phloem tissue for transport around plant
  • loading inorganic ions from soil into root hairs
45
Q

What is the definition of co-transport?

A
  • the coupled movement of substances across a cell membrane via a carrier protein
  • movement of 1 molecule is dependent on movement of the other
46
Q

What is an example of co-transport?

A
  • absorption of glucose + sodium ions from epithelial cells lining the mammalian ileum into the blood
47
Q

Describe the process of co-transport of glucose + sodium ions in the ileum?

A
  • Na+ ions actively transported out of epithelial cell into blood = dec. Na+ conc. in epithelial cell
    • = Na+ conc. gradient between ileum + epithelial cell
  • Na+ ions move into cell from ileum by facilitated diffusion, carrying glucose molecules (against their conc. gradient) w them via a co-transport protein
  • glucose conc. inc. inside epithelial cell, so glucose molecules enter blood via facilitated diffusion
48
Q

What are the factors that the rate of diffusion depends on?

A
  • T°C
  • SA
  • conc. gradient
  • thickness of exchange surface
49
Q

What are the 3 main factors the rate of simple diffusion depends on?

A
  • SA
  • conc. gradient
  • thickness of exchange surface
50
Q

How does surface area affect the rate of simple diffusion?

A
  • larger SA = higher rate
51
Q

How does the conc. gradient affect the rate of simple diffusion?

A
  • greater diff. in conc. on either side of exchange surface = higher rate
52
Q

How does the thickness of the exchange surface affect the rate of simple diffusion?

A
  • thinner = higher rate
53
Q

What are the 2 main factors the rate of facilitated diffusion depends on?

A
  • conc. gradient
  • number of channel or carrier proteins
54
Q

How does the conc. gradient affect the rate facilitated diffusion?

A
  • greater diff. in conc. on either side of exchange surface = higher rate (until all channel/carrier proteins are being used)
55
Q

How does the number of channel or carrier proteins affect the rate of facilitated diffusion?

A
  • greater number of channel or carrier proteins available = higher rate (once all proteins in use = rate can no longer inc.)
56
Q

What are examples of cells adapted for the rapid transport of molecules across their membranes?

A
  • root hair cells
  • epithelial cells of the small intestine
57
Q

How are root hair cells adapted for the rapid transport of molecules across their membrane?

A
  • adapted for absorption of water + mineral ions from soil
  • specialised shape to inc. cell’s SA = inc. rate of water uptake by osmosis
  • thinner walls so water can move through easily
  • have permanent vacuole w cell sap (more conc. than soil water) = maintains high water potential gradient
58
Q

How are epithelial cells of the small intestine adapted for the rapid transport of molecules across their membrane?

A
  • have microvilli = inc. cell’s SA so inc rate of diffusion of products of digestion
  • each villus has a constant blood supply = continually transports products of digestion away from epithelial cells
    • maintains high conc. gradient
59
Q

What are examples of specialised cell for facilitated diffusion?

A
  • neurones
  • muscle cells
  • some kidney cells
60
Q

What factors or conditions affects the permeability of cell membranes?

A
  • T°C
  • solvent conc.
61
Q

Describe a method to show how T°C affects the permeability of cell membranes.

A
  • using a scalpel cut 5 cubes of beetroot (same size)
  • rinse beetroot pieces to remove any pigment released during cutting
  • add beetroot to diff. test tubes containing 5cm3 of water + place each test tube in a water bath at a diff T°C for 30mins
  • remove beetroot pieces, leaving coloured liquid
  • use colourimeter to measure light absorbance of 5 samples of coloured liquid
62
Q

Describe the results of how T°C affects the permeability of the cell membrane of beetroot.

A
  • as T°C inc., membrane permeability inc. so absorbance inc. bc more pigment is released
    - bc phospholipids in membrane move more bc have more energy = not as tightly packer together inc. permeability

Bio Yr 12: Cell Structure (6 decks)

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