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AQA A Level Biology > 3.2- Chapter 4- Transport across cell membranes > Flashcards

3.2- Chapter 4- Transport across cell membranes Flashcards

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1
Q

What are cells surrounded by?

A

A cell surface membrane.

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2
Q

What additional membranes do eukaryotic cells have?

A

Internal membranes

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3
Q

What are membranes functions?

A

Membranes enable passage and control of the movement of substances across exchange surfaces

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4
Q

What do all membranes have?

A

The same basic structure.

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5
Q

What are membranes also known as?

A

Plasma membranes.

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6
Q

What does the cell surface membrane do?

A
  • Surrounds the cell.
  • Barrier between cytoplasm and environment.
  • Establishes conditions inside and outside the cell.
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7
Q

What does partially permeable mean?

A

Allow some molecules through, but not others.

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8
Q

What do membranes around organelles do?

A
  • Breaks the cell into different compartments and provide a barrier to the cytoplasm.
  • e.g. ensures DNA doesn’t leave the nucleus
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9
Q

What are cell membranes composed of?

A

Phospholipids, proteins, glycoproteins, glycolipids and cholesterol.

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10
Q

What model describes the arrangement of molecules in the membrane and why?

A
  • The fluid mosaic model.
  • Fluid- The phospholipids form a bilayer that is constantly moving, making it flexible.
  • Mosiaic- channel/ carrier protiens, glycolipids, glycoprotiens and cholersterol- scattered around bilayer- vary in size and shape and embedded like tiles.
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11
Q

Describe the bilayer.

A
  • Continuous double layer.
  • Hydrophobic tails point in.
  • Hydrophilic heads face out.
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12
Q

What do most molecules not do across membranes and why?

Hint: To do with diffusion

A

Most molecules do not freely diffuse across membranes because they are:
1. Lipid insoluable- can’t pass bilayer
2. Too large to go through channel protiens
3. Same charge as channel protiens so repelled
4. Electrically charged (polar)- difficulty passing through non-polar hydrophoic tails

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13
Q

What are channel protiens specific to?

A

Different molecules

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14
Q

Label the pic of the cell membrane on page 2 of the question print out.

A

Answers on revision card

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15
Q

What do phospholipids form and how do they form it?

A
  • Phospholipids form a bilayer
  • Hydrophillic phosphate heads face outwards on both sides as attracted to water
  • Hydrophobic fatty acid tails- point inwards towards the centre- repelled by water.
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16
Q

What does the phospholipid bilayer form a barrier to and what can freely diffuse across it?

A
  • Forms a barrier to water soluble lipid insoluble substances. at the centre eg ions can’t diffuse through prevents them from entering and leaving the cell.
  • Lipid soluble substances can enter and leave the cell.
  • Small nonpolar lipid-soluble substances e.g. CO2 and water can diffuse through the cell.
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17
Q

What are the properties of the phospholipid bilayer?

A
  • Flexible
  • Self-sealing
  • Constantly moving- fluid
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18
Q

Where can proteins be found within the bilayer?

A
  • Embedded at the surface.
  • Embedded one side to the other of the membrane.
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19
Q

What do proteins at the surface of the membrane do?

A
  • Perform cell signalling- communication between cells.
  • Provide mechanical support
  • Act as receptor protiens to detect and respond to chemicals e.g. hormones- insulin- glucose absorbtion.
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20
Q

What do proteins that span one side of the membrane to the other do?

A
  • Channel protiens- allow water-soluable ions to diffuse
  • Carrier protiens- bind to large molecules e.g. glucose and amino acids and change shape to move them.
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21
Q

Describe the movement of proteins in the cell membrane.

A

Some protiens able to move side to side, others more fixed.

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22
Q

What are the overall functions of proteins in the cell membrane?

A
  • Structural support
  • Channels protiens for facilitated diffusion of water-soluable substances
  • Carrier protiens for facilitated diffusion of large molecules and active transport.
  • Cell identification (antigens)
  • Cell-surface receptors
  • Help cells adhere
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23
Q

What are glycoproteins?

A

Proteins with carbohydrates attached.

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24
Q

What the glycoproteins do in the cell membrane?

A
  • Act as cell surface-receptors for hormones and neurotransmitters.
  • Act as cell recognition sites (antigens), allowing cells to recognise each other, e.g. lymphocytes.
  • Help cells attach to one another and form tissues.
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25
Q

What are glycolipids and where can they be found?

A
  • Lipids with carbohydrates attached.
  • Extend from the bilayer to outside the cell.
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26
Q

What the glycolipids do in the cell membrane?

A
  • Act as cell surface receptors for chemicals
  • Act as cell recognition sites
  • Maintain the stability of the membrane
  • Help cells attach to each other and form tissues.
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27
Q

Where is cholesterol found in the cell membrane and what is it?

A
  • Embedded between phospholipids
  • Present in all cell membranes except bacteria
  • Type of lipid
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28
Q

What are cholesterol’s properties and functions in the cell surface membrane?

A
  • Very hydrophobic prevents loss of water and water soluble ions from entering the cell.
  • Binds hydrophobic tails of phospholipids together to limit their movement without making them too rigid. Moves the molecules closer together to make them** less fluid and more rigid**, reduces lateral movement.
  • Maintains the shape of animal cells- useful when they aren’t supported by other cells.
29
Q

What factors affect the permeability of the cell membrane?

A
  • Temperature
  • Solvents
30
Q

How to solvents affect the permeability of the cell membrane?

A

Higher concentration e.g. of alcohol increases the permeability of the membrane as it dissolves the lipids, causing the membrane to lose its structure.

31
Q

How does temperature affect the permeability of the cell membrane?

A
  • Affects how phospholipids move.
  • Less than 0℃- Phospholipids- limited KE- don’t move much- packed closely together and rigid. Channel and carrier proteins denature due to low temp- increasing permeability. Ice crystals- pierce membrane- makes more permeable when it thaws.
  • 0-45℃- KE increases- phospholipids move around- not packed together so tightly. Membrane- becomes more permeable- temperature increase- movement and kinetic energy increase- phospholipids further apart and more permeable.
  • 45℃+- Bilayer starts to break down and become more permeable. Water expands and puts pressure on membrane. Channel and carrier proteins denature and can’t control what enters or leaves a cell leading to damage to the membrane and increased fluidity. Permeability increases.
32
Q

Draw the graph of the permeability of membranes.

A

Answer on revision card.

33
Q

Why are beetroot cells used in the permeability experiment?

A

Contain a pigment that is easy to see when released from membrane.

34
Q

How do you perform the permeability experiment and give expected results.

A
  1. Cut 5 equal sized pieces of beetroots and rinse to remove any pigments from cutting
  2. Add to 5 different test tubes with 5cm3 water or different concentrations of alcohol depending on which experiment.
  3. Place each test tube in a water bath at different temperatures and for the same length of time, or the same temperature for solvents.
  4. Remove the beetroot, but keep the coloured liquid
  5. Set up a colourimeter using a blue filter. Add distilled water to the cuvette and put in colourimeter holding the frosted sides. Calibrate to zero.
  6. Put the beetroot liquids in the cuvette, filling them to 3/4 full.
  7. Put a quiver in the colorimeter and read absorbance repeat with all samples.
  8. Higher absorbance = higher pigment = higher permeability.
35
Q

What type of transport is simple diffusion?

A

Passive transport.

36
Q

Where does the energy for simple diffusion come from?

A

The energy for simple diffusion comes from natural energy of particles All particles are constantly in motion due to their kinetic energy and move randomly and bounce off each other and the vessels.

37
Q

What is simple diffusion?

A
  • Net movement of molecules or ions from a region of high concentration to a region of low concentration. until particles are evenly distributed.
  • Particles diffuse down the concentration gradient and diffuse as long as they are free to move.
38
Q

What property of cell membranes only allows a small number of molecules through and what must these molecules be?

A

Cell membranes are highly selective- only small non-polar molecules can pass through. e.g. CO2 and O2

39
Q

What factors affect the rate of diffusion?

A
  • Concentration gradient- higher= increased rate difference decreases until equilibrium- reached- slows down over time.
  • Thickness of surface- thinner= shorter distance of travel= faster rate.
  • Increase surface area= increased rate.
40
Q

What type of transport is facilitated diffusion and what does it rely on?

A
  • Passive transport
  • Relies on natural KE of molecules
41
Q

What does facilitated diffusion enable?

A

Enables charged ions and polar molecules to diffuse, as well as larger molecules, (e.g. amino acids, glucose) which diffuse slowly through the bilayer.

42
Q

What is facilitated diffusion?

A
  • Movement of particles from a region of high concentration to a region of low concentration down the concentration gradient through carrier/ channel proteins.
  • High concentration to low concentration using the natural kinetic energy of particles.
43
Q

How’s the carrier proteins perform facilitated diffusion and what do they perform it on?

A
  • Carrier proteins move large molecules
  • Specific different for different molecules
  • Span the whole bilayer.
  • If a specific molecule binds with the protein, protein, the protein changes shape and the molecule is released on the opposite side.
44
Q

How to channel proteins perform facilitated diffusion? And what do they perform at home?

A
  • Allow charged particles aka ions to diffuse.
  • Selective -only open in the presence of specific water souable ions otherwise closed
  • Controls the exit and entry of ions
  • Controls the entry and exit of ions
  • Ions bind causing the protein to change shape- tertiary structure- closes one side and opens on the other, forming water filled hydrophilic channels.
45
Q

Draw a channel protein and a carrier protein and their process.

A

Answer on revision card.

46
Q

What factors affect facilitated diffusion?

A
  • The concentration gradient higher= faster until equilibrium is reached and rate levels off. Rate proportional until carrier prottiens all occupied. If greater substrate concentration- rate only increases slightly as many protiens are used.
  • Number of channels / carrier proteins - if all used rate cannot get faster - even if increased concentration gradient - limiting.
47
Q

How do you calculate the rate of diffusion of the graph?

A

Find the gradient of the graph/ tangent.

48
Q

What type of transport is osmosis?

A

Passive transport.

49
Q

What is osmosis?

A

The diffusion of water across a partially permeable membrane from a region of high water potential to a region of low water potential down the water potential gradient.

50
Q

What is the symbol for water potential?

A

ψ

51
Q

What is water potential and how is it measured?

A
  • Water potential (ψ) is measured in PSI and is a measure of the pressure created by water molecules
  • Water potential can also define the likelihood of water molecules to diffuse out of or into a solution
52
Q

What is the water potential of pure water?

A

0ψ

53
Q

What is the effect of solute on water potential and why?

A
  • More solute creates a reduced water potential as more molecules move out of the solution.
  • Solutes make the water potential negative.
  • This this is because the partially permeable membrane only allows small water molecules are molecules across but not large solute. The water molecules diffuse but not solute molecules until the water potential on each side is equal and dynamic equilibrium is reached.
54
Q

Define isotonic and what its effect is on the cell.

A
  • Isotonic solutions have the same water potential as inside the cell- no net movement of water molecules
  • If a cell is placed in this type of solution, its size doesn’t change, so most cells live in isotonic solutions.
55
Q

Define hypotonic and its effect on the cell.

A
  • Hypotonic solutions - less solute - high water potential
  • Cell swells and absorbs water- membrane bursts as thin and not very flexible.
56
Q

Define hypertonic and its effect on the cell.

A
  • Hypertonic solutions- more solute- lower water potential
  • Cell shrinks - water leaves- plant cells plasmolysed as the cell membrane pulls away from the cell wall.
57
Q

What factors affect osmosis?

A
  • Water potential gradient increased = increased rate. Over time the rate slows and levels off as difference decreases
  • Thickness of surface - thinner = faster rate of osmosis
  • Surface area- increased = increased rate of osmosis
58
Q

Describe the experiment to measure water potential.

A
  1. Make serial dilutions- decrease dilutions by a factor each time e.g. add five centimetres of solution to 5 centimetres of distilled water, then take five centimetres of that solution and repeat, or use 1:9 to create a better representation e.g. factor 10
  2. Measure change in mass- cut potatos into identical sized chips- make sure the same number of sides exposed- divide into 3 for each concentration, dry rolling over a cloth, weigh chip, put into solution at the same temperature with the water bath, remove at a set time (same for each chip), dry, weigh and calculate the percentage of mass. Repeat at other concentrations.
  3. Produce a calibration curve of percentage change in mass against concentration- where change in mass= 0 is the solution with the water potential of the potato as the solution and the potato are isotonic. Research the water potential of the solution to find the water potential.
59
Q

What is active transport?

A

Movement of molecules or ions through a partially permeable membrane against the concentration gradient from a region of lower concentration to a region of higher concentration using ATPs metabolic energy to change the shape of carrier protiens.

60
Q

How is active transport different to facilitated diffusion?

A
  • Against the concentration gradient
  • Requires ATP hydrolysis
  • Only carrier protiens not channel protiens.
61
Q

How is active transport facilitated?

A
  1. Carrier proteins act as pumps span the plasma membrane.
  2. Bind to molecules or ions.
  3. ATP hydrolyses on the other side and relases a phosphate ion that binds to the carrier protien and causes it to change shape and open.
  4. The molecule is relased on the opposite side
  5. The phosphate is released from the protien and the protien reverts back to its original shape ready to repeat.
  6. Phosphate ions rejoin to ADP in respiration ot form ATP.
62
Q

What is another form of active transport and describe it?

A

Co-transport.
When one molecule is moved another molecule is added or the concentration gradient of one molecule is used to move the other molecule against it’s concentration gradient.

63
Q

Describe the sodium potassium pump and what it is used for.

A
  • The sodium potassium pump is a form of co-transport
  • When one molecule is removed, one molecule is added- sodium removed and potassium added.
  • Uses one molecule of ATP to move both sodium and potassium
  • Na+ binds on the inside of the pump
  • ATP is hydrolysed and the phosphate ion binds to the outside of the pump.
  • The protien changes shape due to the interaction of bonds and sodium ions are moved outside the cell.
  • K+ ions bind to the outside and the phosphate ion is released
  • As the protien reverts to its original shape the potassium ion moves to the other side of the membrane.
  • Used in nerve impulses.
64
Q

What factors affect the rate of active transport?

A
  • Speed of carrier proteins increasing increases rate.
  • Numbers carrier proteins present increasing increases rate.
  • Rate of respiration and availability of ATP
65
Q

What is co-transport used for?

A

Used to absorb glucose and amino acids so they remain inside the body.

66
Q

How does co-transport work?

A
  • Co-transporters are carrier proteins
  • Bind to two different molecules at a time.
  • The concentration gradient of one molecule moves the other molecule against it’s concentration gradient.
67
Q

Give an example of when co-transport is used and explain why it is used.

A
  • The absorbtion of glucose using sodium ions in the end part of the small intestines- mammelian ileum.
  • Glucose (and amino acids) can’t diffuse as at the end of the intestines so concentration too small so co-transport is used instead.
68
Q

Describe the movement of glucose in illeum cells.

A
  1. Sodium ions are actively transported out of epithelial cells by a sodium- potassium pump and into the blood. Creates a concentration gradient- higher concentration of Na+ ions in the lumen of the illeum than the epithelial cells.
  2. Sodium ions diffuse by co-transport/ facilitated diffusion from the lumen of the ileum into epithelial cells down the concentration gradient through a sodium glucose co-transporter protein- glucose and sodium move into the cell and the glucose concentration increases.
  3. Glucose diffuses into the blood by facilitated diffusion through channel protiens.
69
Q

How have cells been adapted for rapid transport across their membranes and what affects the rate of transport.

A
  • Increased surface area e.g. folded membranes for diffusion= faster rate. For simple diffusion and osmosis. e.g. epithelial cells and microvilli.
  • Increased number of carrier/ channel protiens- increased rate for facilitated diffusion, co-transport and active transport. Once all in use can’t happen any faster.
  • Speed of carrier protiens increased= increased rate for facilitated diffusion, co-transport and active transport.
  • Concentration/ water potential gradient- increased= increased rate- for diffusion and osmosis. Difference between 2 sidea town until dynamic equilibrium is reached- rate slows down over time.
  • Thickness of exhchange surface- simple diffusion and osmosis- thinner= faster as particles have to travel shorter distance
  • Rate of respiration and availability of ATP- increased= increased active transport e.g. increased mitochondria to increase ATP

AQA A Level Biology (13 decks)

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