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A-level Biology > 5 - Plasma Membranes🫙 > Flashcards

5 - Plasma Membranes🫙 Flashcards

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1
Q

Active Transport

Define active transport

A

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

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2
Q

Active Transport

What does this process require?

A

Carrier proteins and metabolic energy (supplied by ATP)

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3
Q

Active Transport

Where / what do carrier proteins do?

A

Span the membranes and act as ‘pumps’

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4
Q

Active Transport

Outside to inside a cell

Step 1 = the molecule or ion to…

A

be transported binds to receptors in the channel of the carrier protein on the outside of the cell

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5
Q

Active Transport

Outside to inside a cell

Step 2 = on the inside of the cell, ATP…

A

binds to the carrier protein and is hydrolysed into ADP and phosphate

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6
Q

Active Transport

Outside to inside a cell

Step 3 = binding of the phosphate molecule to…

A

The carrier protein causes the protein to change shape, opening up the inside of the cell

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7
Q

Active Transport

Outside to inside of cell

Step 4 = the molecule or ion is…

A

released to the inside of the cell

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8
Q

Active Transport

Outside to inside of a cell

Step 5 = the phosphate molecule is released from…

A

the carrier protein and recombines with ADP to form ATP

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9
Q

Active Transport

Outside to inside of a cell

Step 6 = the carrier protein…

A

returns to its original shape

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10
Q

Active Transport

What does it mean if the process is selective?

A

Specific substances are transported by specific carrier proteins

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11
Q

Active Transport

What is bulk transport?

A

Large molecules too large to move through channel or carrier proteins are moved into and out of the cell by bulk transport

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12
Q

Active Transport

What large molecules are transported by bulk transport?

A

Enzymes, hormones, bacteria

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13
Q

Bulk Transport

What are the two types of endocytosis?

A

Phagocytosis for solids
Pinocytosis for liquids

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14
Q

Bulk Transport

Endocytosis

What happens first in both types as the membranes comes into contact with the material being transported?

A

Cell-surface membrane invaginates (bends inwards), enfolding the material until the membrane fuses forming a vesicles

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15
Q

Bulk Transport

Endocytosis

What happens once the vesicle is formed?

A

It pinches off and moves into the cytoplasm to transfer the material for further processing within the cell

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16
Q

Bulk Transport

Endocytosis

Give an example of where/why the vesicles are further processed in the cell

A

Vesicles containing bacteria are moved towards lysosomes where bacteria can be digested by enzymes

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17
Q

Bulk transport

Exocytosis

How does exocytosis work?

A

Vesicles usually formed by the Golgi move towards and fuse with the cell surface membrane. The contents of the vesicles are then released

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18
Q

Bulk Transport

Exocytosis

What is it?

A

Movement to the OUTSIDE of a vell

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19
Q

Why is energy (ATP) required for vesicles?

A
  • movement along cytoskeleton
  • changing shape = engulfing
  • fusion to membranes
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20
Q

Factors affecting membrane structure

How do phospholipids get more KE so they can move more than they already do?

A

Temperature

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21
Q

Factors affecting membrane structure

Why does more movement harm a membrane?

A

Makes it more fluid = begins to lose its structure = breaks down completely

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22
Q

Factors affecting membrane structure

What can the loss of structure from high temp increase?

A

The permeability of the membrane, making it easier for particles to cross it

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23
Q

Factors affecting membrane structure

What happens to carrier and channel proteins in high temp?

A

Denature, affecting membrane permeability

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24
Q

Factors affecting membrane structure

What is essential in the formation of a phospholipid bilayer?

A

Water, a polar solvent

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25
Q

Factors affecting membrane structure

Are organic solvents more or less polar than water?

A

Less, such as alcohol

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26
Q

Factors affecting membrane structure

What do organic solvents do to membranes?

A

Dissolve membranes, disrupting cells

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27
Q

Factors affecting membrane structure

Why are alcohols used in antiseptic wipes?

A

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

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28
Q

Factors affecting membrane structure

Why are pure or very strong alcohol solutions toxic?

A

They destroy cells in the body

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29
Q

Factors affecting membrane structure

What do alcoholic drinks do to membranes?

A

Can enter the cell membrane and the presence of these molecules between the phospholipids disrupts the membranes

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30
Q

Factors affecting membrane structure

What happens when the membrane is disrupted?

A

Becomes more fluid = more permeable

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31
Q

Factors affecting membrane structure

Give an example of cells that need intact cell membranes for specific functions

A

The transmission of nerve impulses by neurones (nerve cells)

When these are disrupted, nerve impulses are no longer transmitted as normal

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32
Q

Factors affecting membrane structure

Why do peoples’ behaviour change after consuming alcoholic drinks?

A

The neurones in the brain are no longer transmitted as normal

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33
Q

Investigating membrane permeability

What is the red pigment in beetroot called?

A

Betalain

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34
Q

Investigating membrane permeability

Why is betalain useful in this experiment?

A

The red pigment is released and the surrounding solution is coloured when membranes are disrupted

The amount of pigment released is related to the disruption

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35
Q

What is described as either active or passive?

A

The exchange of substances between cells and their environment

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36
Q

Is diffusion active or passive?

A

Passive transport

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37
Q

How does passive movement get energy?

A

Utilises energy from the natural motion of particles rather than from another soruce

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38
Q

Define diffusion

A

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

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39
Q

How long will diffusion go on for?

A

Until an equilibrium is reached

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40
Q

Why does diffusion happen?

A

Because particles have energy so the random and unequal distribution of particles will move to become equal

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41
Q

What slows down particles movements

A

The high speed collisions

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42
Q

When is diffusion faster?

A

Over short distances as fewer collisions occur

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43
Q

Factors affecting rate of diffusion

The higher the temperature =

A

more KE = higher rate of diffusion

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44
Q

Factors affecting rate of diffusion

Greater concentration difference =

A

faster rate of diffusion = larger overall movement

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45
Q

How can diffusion be calculated?

Two ways

A
  • By distance travelled / time
  • by volume filled / time
46
Q

When is diffusion not as easy?

A

When the hydrophobic interior of the membrane repels substances with a positive or negative change (ions

47
Q

Can polar molecules (such as water) diffuse?

A

Yes but at a slow rate

48
Q

The rate at which molecules or ions diffuse across membranes is affected by:

A

SA = the larger the exchange surface, high rate

Thickness of membrane = the thinner the exchange surface, high rate

49
Q

Phospholipid bilayer membranes are barriers to what?

A

Polar molecules and ions

50
Q

How do polar molecules and ions pass a membrane?

A

Through channel proteins

51
Q

What is diffusion across a membrane through protein channels called?

A

Facilitated diffusion

52
Q

What quality do membranes with protein channels have?

A

They are selectively permeable as most protein channels are specific to one molecule or ion

53
Q

What is the rate of facilitated diffusion dependent on?

A
  • temperature
  • conc gradient
  • SA
  • thickness
  • number of channel proteins present
54
Q

Which proteins does facilitated diffusion need?

A

Channel and carrier

55
Q

Define osmosis

A

The net movement of water across a partially permeable membrane from a region of higher water potential to a region of lower water potential

56
Q

Define a solute

A

A substance dissolved in a solvent, forming a solution

57
Q

Define water potential

A

The pressure exerted by water molecules as they collide with a membrane or cobtainer

58
Q

What is water potential measured in?

A

Pressure pascals (Pa) or kilopascal (kPa)

59
Q

What is the symbol for water potential?

A

The Greek letter psi

60
Q

What water potential does pure water have?

A

0 kPa

61
Q

Why is 0kPa the highest possible value for water potential?

A

As the presence of a solute in water lowers the water potential below 0

62
Q

Why happens to water potential in a more concentrated solution?

A

The more negative the water potentiak

63
Q

Effects of Osmosis on Animal Cells

What happens if an animal cell is placed in a solution with a higher water potential than that of the cytoplasm?

A

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

64
Q

Define hydrostatic pressure

A

The diffusion of water into a solution leads to an increase in volume of this solution. It the solution is in a closed system (eg. A cell) this results in an increase in pressure

65
Q

What are the units for hydrostatic pressure?

A

kPa

66
Q

Effects of Osmosis on Animal Cells

Explain the event of cytolysis

A
  • the cell-surface membrane cannot stretch much and can’t withstand the increased hydrostatic pressure
  • it will break and the cell will burst
67
Q

Effects of Osmosis on Animal Cells

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

68
Q

Effects of Osmosis on Animal Cells

What is caused by a loss of water to the solution by osmosis down the water potential gradient?

A

Causes a reduction in the volume of the cell and the cell-surface membrane to ‘pucker’ referred to as crenation

69
Q

Effects of Osmosis on Animal Cells

What do multicellular animals usually have to prevent cytolysis or crenation?

A

Control mechanisms to make sure thei cells are continuously surrounded by aqueous solutions with an equal water potential = isotonic

In blood the aq solution is blood plasma

70
Q

Effects of Osmosis on Plant Cells

How are animal and plant cells similar?

A

contain a variety of solutes, mainly dissolved in a large vacuole

71
Q

Effects of Osmosis on Plant Cells

How are animal and plant cells unlike?

A

Plants are unable to control the water potential or the fluid around them

Eg roots are surrounded by almost pure water

72
Q

Effects of Osmosis on Plant Cells

What does the increased hydrostatic pressure due to osmosis cause?

A

Pushes the membranes against the rigid cell walls = turgor

73
Q

Effects of Osmosis on Plant Cells

What happens as the turgor pressure increases?

A

It resists the entry of further water and the cell is said to be turgid

74
Q

Effects of Osmosis on Plant Cells

What happens when plant cells are placed in a solution with a lower water potential than their own?

A

Water is lost from the cells by osmosis

75
Q

Effects of Osmosis on Plant Cells

What does water lost from the cells by osmosis lead to?

A

Reduction in the volume of the cytoplasm

76
Q

Effects of Osmosis on Plant Cells

What does reduction in the volume of the cytoplasm cause?

A

Pulls the cell-surface membrane away from the cell wall - the cell is said to be plasmolysed

77
Q

What forms a membrane?

A

A phospholipid bilayer

78
Q

Where do cells normally exist?

A

In aqueous environments

79
Q

What is the head of a phospholipid?

A

Charged hydrophilic head

80
Q

What is the tail of a phospholipid?

A

Hydrophobic fatty acids tails

81
Q

Who created the fluid-mosaic model and when?

A

1972 Singer and Nicholson

82
Q

Why is it a FLUID mosaic model?

A

Because the phospholipid said are free to move within the layer relative to each other

83
Q

What does fluidity give a membrane?

A

Flexibility

84
Q

Why is it a fluid MOSAIC model?

A

Because the proteins embedded in the bilayer vary in shape, size and position

85
Q

What do plasma membranes contain?

A

Various proteins and lipids - the type and number of which are particular to each cell

86
Q

What important role do membrane proteins have?

A

the various functions of membranes

87
Q

What type of membrane proteins are there?

A

Intrinsic and extrinsic proteins

88
Q

Intrinsic Proteins

Define integral proteins

A

Are transmembrane proteins that are embedded through both layers of a membrane

89
Q

Intrinsic Proteins

What do intrinsic proteins have?

A

Amino acid with hydrophobic R-groups on their external surfaces, which interact with the hydrophobic core of the membrane keeping them in place

90
Q

Intrinsic proteins

What do channel proteins provide?

A

A hydrophilic channel that allows passive movement of polar molecules and ions down a conc gradient through membranes

91
Q

Intrinsic Proteins

How are channel proteins held in position?

A

By interactions between the hydrophobic core of the membrane and the hydrophobic R-groups on the outside of the proteins

92
Q

Intrinsic Proteins

What do carrier proteins have a role in?

A

Both active and passive transport

93
Q

Intrinsic Proteins

What do carrier proteins often have to do?

A

Change shape

94
Q

Intrinsic Proteins

Where are glycoproteins found?

A

Embedded in the cell-surface membrane with attached carbohydrate chains

95
Q

Intrinsic Proteins

What role do glycoproteins play?

A

In cell adhesion and as receptors for chemical signals

96
Q

Define cell adhesion

A

When cells join together to form tight junctions in certain tissues

97
Q

Intrinsic Proteins

What happens when chemicals bind to the receptor?

A

It elicits a response from the cell. This msg cause a direct response or set off a cascade of events inside the cell

This is known as cell signalling

98
Q

Give examples of cell signalling

A
  • receptors for neurotransmitters such as acetylcholine at nerve cell synapses
  • receptors for peptide hormones which affect the uptake and storage of glucose by crlls
99
Q

Intrinsic Proteins

How do Beta blockers work?

A

Act by binding to cell receptors and are used to reduce the response of the heart to stress

100
Q

Intrinsic Proteins

What are glycolipids similar to?

A

Glycoproteins

101
Q

Intrinsic Proteins

What are glycolipids?

A

Lipids with attached carbohydrate chains

102
Q

Intrinsic Proteins

What can glycolipids be called?

A

Cell markers / antigens

103
Q

Intrinsic Proteins

What is the role of glycolipids?

A

Be recognised by the cells of the immune system as self or non-self

104
Q

Extrinsic proteins

Where are extrinsic/peripheral proteins found?

A

Present in one side of the bilayer and can move between layers

105
Q

Extrinsic proteins

What do they normally have in their outer surface?

A

Hydrophilic R-groups

106
Q

Extrinsic proteins

What do they interact with?

A

With the polar heads of the phospholipids or with intrinsic proteins

107
Q

Extrinsic proteins

What is cholesterol?

A

A lipid with a hydrophilic and hydrophobic end that regulates the fluidity of a membrane

108
Q

Extrinsic proteins

Where are cholesterol molecules positioned?

A

Between phospholipids in a membrane bilayer

109
Q

Extrinsic proteins

What does cholesterol do to the bilayer?

A

Add stability without making then too rigid

110
Q

Extrinsic proteins

What does cholesterol prevent?

A

Membranes becoming too solid by stopping the phospholipid molecules from grouping too closely and crystallising

111
Q

Membranes can be the site of…

A

Chemical reactions

112
Q

Mark Scheme Points

How does cholesterol affect fluidity?

A
  • binds to fatty acid tails
  • increasing the packing of membrane
  • therefore reducing the fluidity/permeability
  • makes the membrane less permeable to very small water-soluble molecules

A-level Biology (23 decks)

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