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A level Biology Paper 1- Core concepts > Cell Membranes and Transport > Flashcards

Cell Membranes and Transport Flashcards

1
Q

What is the cell membrane selectively permeable to?

A

-water and some liquids

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2
Q

how do liquid soluble substances and water soluble substances move through the cell membrane?

A

lipid soluble substances move more easily through the cell membrane

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3
Q

What are lipid soluble substances?

A

-small uncharged molecules
-non-polar substances

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4
Q

How do small uncharged molecules move through the cell membrane?

A

-small uncharged molecules, such as oxygen and carbon dioxide, dissolve in the hydrophobic tails of the phospholipids and diffuse across the cell membrane

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5
Q

how do non-polar substances move through the cell membrane?

A

-non-polar substances, such as vitamin A, can also dissolve in phospholipids and diffuse through cell membranes

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6
Q

What are water soluble substances?

A

polar molecules, such as glucose and amino acids

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7
Q

how do polar molecules move through the cell membrane?

A

-polar molecules such as glucose and amino acids as well as charged ions, e.g. Na+ cannot easily diffuse through the phospholipids
-they pass through intrinsic protein molecules (channels or carrier proteins)

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8
Q

What is the permeability of the membrane affected by?

A

-Temperature
-Organic Solvent
-Type of diffusing molecule

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9
Q

how does temperature affect membrane permeability?

A

-increased temperature increases membrane permeability as the molecules moving through the membrane will have more kinetic energy and will diffuse more quickly

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10
Q

How do organic solvents (e.g. ethanol) affect the permeability of the membrane?

A

-ethanol dissolves/emulsifies the phospholipids and may denture other proteins resulting in gaps or holes within the membrane/the membrane becomes more porous
-Acetone has a similar effect to ethanol

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11
Q

what are the methods of transport across the membrane?

A

Passive:
-Diffusion
-Facilitated Diffusion
-Co-transport
-Osmosis
Active:
-Active Transport
-Bulk transport (endo/exocytosis)

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12
Q

what is diffusion?

A

The passive movement of a molecule or ion down a concentration gradient, from a region of higher concentration to a region of lower concentration

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13
Q

what does passive mean?

A

Not requiring ATP provided by the cell

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14
Q

Why must there be a difference in concentration for diffusion?

A

If there is an equilibrium, there will be no net movement

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15
Q

What are factors affecting the rate of diffusion?

A

-The concentration gradient
-The thickness of the surface
-The surface area of the membrane
-The size of the diffusing molecule
-The nature of the diffusing molecule
-Temperature

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16
Q

how does the concentration gradient affect the rate of diffusion?

A

-The greater the difference in concentration of molecules in 2 areas, the molecules will diffuse in the given time

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17
Q

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

A

-The shorter the distance over which diffusion takes place, the more will diffuse in the given time

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18
Q

How does the surface area of the membrane affect the rate of diffusion?

A

The larger the area the higher the number of molecules that will diffuse in the given time

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19
Q

How does the size of the diffusing molecule affect the rate of diffusion?

A

-smaller molecules diffuse faster than large molecules (more kinetic energy)

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20
Q

how does the nature of the diffusing molecule affect the rate of diffusion?

A

-molecules that are soluble in phospholipid (non-polar) diffuse faster than water molecules (polar) because they can diffuse anywhere through the membrane

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21
Q

How does temperature affect the rate of diffusion?

A

-Increased temperature increases the rate of diffusion as the molecules or ions (or phospholipid bilayer) have more kinetic energy

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22
Q

What is facilitated diffusion?

A

-The passive transfer of polar molecules or charged ions down a concentration gradient, across a membrane, by channel or carrier proteins in the membrane

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23
Q

What is facilitated diffusion used to do?

A

-used to transport ions in large, polar molecules, such as Na+, glucose and amino acids that are relatively insoluble in phospholipids

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24
Q

Why is facilitated diffusion passive?

A

Does not require ATP

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25
Q

why is facilitated diffusion more rapid than simple diffusion for polar molecules/charged ions?

A

Going through a protein as easier than going directly through the bilayer

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26
Q

What affects the rate of facilitated diffusion through the membrane?

A

-Number of channel/carrier proteins present in the membrane; once they are filled, the rate will plateau
-steepness of the conc grad
-temperature

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27
Q

What are two types of transport proteins?

A

-Channel Proteins
-Carrier Proteins

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28
Q

What are channel proteins?

A

-protein molecules with water filled hydrophilic pores
-Ions being water soluble can pass through because the pores are hydrophilic
-each channel is specific for one type of ion
-channels open and close depending on the needs of the cell

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29
Q

What are carrier proteins?

A

-allow diffusion of large polar molecules, such as glucose and amino acids
-A polar molecule attaches to a binding site on the carrier protein
-This causes the protein to change shape releasing the molecule through to the other side of the membrane

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30
Q

What are specific types of facilitated diffusion?

A

-gated protein channels
-co transport

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31
Q

what do gated protein channels do?

A

-can be opened or closed to allow ions through, for example, sodium ion gated channels that open during initiation of the nerve impulse

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32
Q

What is co transport?

A

-A type of facilitated diffusion that brings molecules and ions into cells together on the same protein transport molecule.

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33
Q

What type of process is co-transport?

A

A passive process, which means that energy in form of ATP not required

34
Q

what is an example of co-transport?

A

Sodium glucose co transport:
-There is a concentration gradient for sodium ions to move into the cell.
-Sodium ions and glucose bind to the carrier protein.
-The carrier protein changes shape, and the sodium ions and glucose are transported to the other side of the membrane.
-This process can move glucose against its concentration gradient without the use of ATP - this is known as secondary active transport.

35
Q

What are two examples of processes that involve uptake of sodium ions and glucose molecules by co-transport?

A
36
Q

What is active transport?

A

-transport of ions and molecules against the concentration gradient

37
Q

What does active transport use?

A

-Energy from the hydrolysis of ATP, made by the cell in respiration

38
Q

what happens if respiration is inhibited (e.g by cyanide poison)?

A

Active transport is also inhibited

39
Q

what does active transport require?

A

an intrinsic carrier protein as in facilitated diffusion, but because transport is against the concentration gradient the process requires energy and the carrier acts as a pump

40
Q

what can be actively transported?

A

Only charged particles, e.g. ions and polar molecules such as glucose that are insoluble in lipid,

41
Q

how does active transport work? (carrier protein)

A

1.The molecule or ion binds to the carrier protein on the outside of the cell membrane.
2. ATP transfers a phosphate group to the carrier protein.
3. The carrier protein changes shape and carries the ion or molecule across the membrane.
4. The molecule or ion is released into the cytoplasm of the cell.
5. The carrier protein returns to its original shape.

42
Q

What are some examples of processes that involve active transport?

A
43
Q

why are cells that perform active transport packed with mitochondria?

A
44
Q

What is bulk transport?

A

-Endocytosis and Exocytosis are the processes where the cell transports materials in bulk into or out of the cell -ATP is required so these are active processes.

45
Q

What is exocytosis (secretion)?

A

The process by which substances may leave the cell having been transported through the cytoplasm in a vesicle, which fuses with the cell membrane.

46
Q

what happens in exocytosis?

A

-A vesicle is produced in the cytoplasm (e.g, budding off at one end of Golgi body).
-The vesicle migrates to plasma membrane, fuses with it and secretes its contents to the outside of the cell. e.g. secretion of the hormone insulin or digestive

47
Q

what happened to the surface area of the cell after exocytosis?

A

Increases

48
Q

What is endocytosis (uptake)?

A

-The cell membrane folds around the particle.
-The folding closes off the link to the outside of the cell, so now the particle is fully trapped inside the cell in a vesicle or vacuole.

49
Q

What are the two types of endocytosis?

A

-Phagocytosis
-Pinocytosis

50
Q

what is phagocytosis?

A

-uptake of solids, e.g. when wbc’s engulf bacteria

51
Q

what is pinocytosis?

A

-uptake of liquids, e.g. lipid droplets

52
Q

what is the process of phagocytosis?

A

-Solid material (e.g. bacteria)
-Plasma membrane folds around solid material
-A vesicle is created containing the solid material
-Later the solid material will be destroyed by enzymes

53
Q

What is osmosis?

A

-Osmosis is the diffusion of water, from an area of higher water potential to an area of lower water potential across a selectively permeable membrane
-it is a passive process so does not require ATP.

54
Q

What is water potential?

A

-Water potential (W) is the tendency for water to leave a solution or cell by osmosis and is measured in kPa.
-(The greater the number of free water molecules in a solution, the higher the water potential).

55
Q

Why is pure water given the highest value of 0 kPa?

A

it has the greatest potential energy to move

56
Q

why are all other solutions given negative values

A

-They have a lower water potential
than pure water

57
Q

What happens as you add a solute to water?

A

•the number of free water molecules is decreased and the potential energy of the water decreases and therefore the water potential becomes more negative
•e.g. a dilute solution may have a water potential of -50 kPa, whereas a more concentrated solution may have a water potential of -100 kPa.

58
Q

what is hypotonic?

A

If the water potential of the external solution is less negative (higher) than the solution inside the cell, water flows into the cell.

59
Q

What is hypertonic?

A

If the water potential of the external solution is more negative (lower) than the solution inside the cell, water flows out of the cell.

60
Q

What is isotonic?

A

If the water potential of the external solution is the same as the solution inside the cell, so there is no net movement of water.

61
Q

from where does water move in terms of water potential?

A

Water moves from an area of higher water potential to an area of lower or more negative water potential.

62
Q

What equation describes the relationship between the forces involved in water potential?

A

water potential=solute potential + pressure potential

63
Q

what is solute potential due to?

A

the solutes in the vacuole and cytoplasm, it is the lowering of water potential due to the presence of solute molecules

64
Q

what does pressure potential?

A

The pressure exerted by the cell contents on the cell wall, a force which increases the tendency of water to move out

65
Q

What is the explanation of pressure potential?

A
  1. Water entering a plant cell by osmosis causes the vacuole
    and cytoplasm to swell. This makes the cell turgid.
    2 .The cell wall is inelastic and so outward pressure builds up as the cytoplasm pushes against the cell wall.
    This pressure is the pressure potential.
66
Q

what happens if a plant cell is placed in a hypotonic solution?

A

-then water will move into the cell by osmosis.
-this causes a plant cell to become TURGID.

67
Q

Why don’t plant cells burst?

A

-The plants are will gain water until it is by the prevented by the opposing cell wall (pressure potential)
-Pressure is generated as the cell wall is inelastic

68
Q

what happens if a plant cell is placed in a hypertonic solution?

A

-water will move out the cell into the surrounding solution by osmosis
-The vacuole shrinks and the cytoplasm and the cell membrane will withdraw from the cell
-This causes the plant cell to become plasmolysed (flaccid)

69
Q

What is incipient plasmolysis?

A

-Incipient plasmolysis for plant cells is theoretically defined as the point at which the cell membrane is just about to come away from the cell wall. -Experimentally, incipient plasmolysis is the point where 50% of the cells in a sample are plasmolysed.

70
Q

at incipient plasmolysis what would water pressure be?

A

-water is entering the cell vacuole, so the cell wall does not exert any pressure, so pressure potential is 0

71
Q

what is the equation for water potential at incipient plasmolyisis?

A
72
Q

Why do animals cells burst in hypotonic solution?

A

-water moves into the cell by osmosis from an area of higher water potential to an area of lower water potential
-The cells cytoplasm swells and the cell bursts (as there is no an elastic cell wall to oppose this pressure)

73
Q

why do animal cells crenate in a hypertonic solution?

A
74
Q

What is the definition of hydrophilic?

A

A molecule that is attracted to water molecules

75
Q

what is the definition of hydrophobic?

A

A molecule that is repelled by water molecules

76
Q

What is the definition of exocytosis?

A

The process by which substances may leave the cell in bulk, having been transported through the cytoplasm in a vesicle, which fuses with the cell membrane.

77
Q

What is the definition of endocytosis?

A

The process by which substances may enter the cell in bulk.

78
Q

What is the definition of hypertonic?

A

A solution with a lower water potential than its surroundings (due to more solute being present).

79
Q

what is the definition of hypotonic?

A

A solution with a higher water potential than its surroundings (due to less solute being present).

80
Q

what is the definition of isotonic?

A

A solution with the same water potential as its surroundings.

81
Q

What is the definition of solute potential?

A

Due to the solutes in the vacuole and cytoplasm, it is the lowering of water potential due to the presence of solute molecules.

82
Q

What is the definition of pressure potential?

A

The pressure exerted by the cell contents on the cell wall, a force which increases the tendency of water to move out.

A level Biology Paper 1- Core concepts (5 decks)

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