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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
Factors affecting membrane structure Are organic solvents more or less polar than water?
Less, such as alcohol
26
Factors affecting membrane structure What do organic solvents do to membranes?
Dissolve membranes, disrupting cells
27
Factors affecting membrane structure Why are alcohols used in antiseptic wipes?
The alcohols dissolve the membranes of bacteria in a wound, killing them and reducing the risk of infection
28
Factors affecting membrane structure Why are pure or very strong alcohol solutions toxic?
They destroy cells in the body
29
Factors affecting membrane structure What do alcoholic drinks do to membranes?
Can enter the cell membrane and the presence of these molecules between the phospholipids disrupts the membranes
30
Factors affecting membrane structure What happens when the membrane is disrupted?
Becomes more fluid = more permeable
31
Factors affecting membrane structure Give an example of cells that need intact cell membranes for specific functions
The transmission of nerve impulses by neurones (nerve cells) When these are disrupted, nerve impulses are no longer transmitted as normal
32
Factors affecting membrane structure Why do peoples’ behaviour change after consuming alcoholic drinks?
The neurones in the brain are no longer transmitted as normal
33
Investigating membrane permeability What is the red pigment in beetroot called?
Betalain
34
Investigating membrane permeability Why is betalain useful in this experiment?
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
35
What is described as either active or passive?
The exchange of substances between cells and their environment
36
Is diffusion active or passive?
Passive transport
37
How does passive movement get energy?
Utilises energy from the natural motion of particles rather than from another soruce
38
Define diffusion
The net movement of particles from a region of higher concentration to a region of lower concentration
39
How long will diffusion go on for?
Until an equilibrium is reached
40
Why does diffusion happen?
Because particles have energy so the random and unequal distribution of particles will move to become equal
41
What slows down particles movements
The high speed collisions
42
When is diffusion faster?
Over short distances as fewer collisions occur
43
Factors affecting rate of diffusion The higher the temperature =
more KE = higher rate of diffusion
44
Factors affecting rate of diffusion Greater concentration difference =
faster rate of diffusion = larger overall movement
45
How can diffusion be calculated? Two ways
- By distance travelled / time - by volume filled / time
46
When is diffusion not as easy?
When the hydrophobic interior of the membrane repels substances with a positive or negative change (ions
47
Can polar molecules (such as water) diffuse?
Yes but at a slow rate
48
The rate at which molecules or ions diffuse across membranes is affected by:
SA = the larger the exchange surface, high rate Thickness of membrane = the thinner the exchange surface, high rate
49
Phospholipid bilayer membranes are barriers to what?
Polar molecules and ions
50
How do polar molecules and ions pass a membrane?
Through channel proteins
51
What is diffusion across a membrane through protein channels called?
Facilitated diffusion
52
What quality do membranes with protein channels have?
They are selectively permeable as most protein channels are specific to one molecule or ion
53
What is the rate of facilitated diffusion dependent on?
- temperature - conc gradient - SA - thickness - number of channel proteins present
54
Which proteins does facilitated diffusion need?
Channel and carrier
55
Define osmosis
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
Define a solute
A substance dissolved in a solvent, forming a solution
57
Define water potential
The pressure exerted by water molecules as they collide with a membrane or cobtainer
58
What is water potential measured in?
Pressure pascals (Pa) or kilopascal (kPa)
59
What is the symbol for water potential?
The Greek letter psi
60
What water potential does pure water have?
0 kPa
61
Why is 0kPa the highest possible value for water potential?
As the presence of a solute in water lowers the water potential below 0
62
Why happens to water potential in a more concentrated solution?
The more negative the water potentiak
63
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?
Water will move into the cell by osmosis, increasing the hydrostatic pressure inside the cell
64
Define hydrostatic pressure
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
What are the units for hydrostatic pressure?
kPa
66
Effects of Osmosis on Animal Cells Explain the event of cytolysis
- the cell-surface membrane cannot stretch much and can’t withstand the increased hydrostatic pressure - it will break and the cell will burst
67
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?
It will lose water to the solution by osmosis down the water potential gradient
68
Effects of Osmosis on Animal Cells What is caused by a loss of water to the solution by osmosis down the water potential gradient?
Causes a reduction in the volume of the cell and the cell-surface membrane to ‘pucker’ referred to as crenation
69
Effects of Osmosis on Animal Cells What do multicellular animals usually have to prevent cytolysis or crenation?
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
Effects of Osmosis on Plant Cells How are animal and plant cells similar?
contain a variety of solutes, mainly dissolved in a large vacuole
71
Effects of Osmosis on Plant Cells How are animal and plant cells unlike?
Plants are unable to control the water potential or the fluid around them Eg roots are surrounded by almost pure water
72
Effects of Osmosis on Plant Cells What does the increased hydrostatic pressure due to osmosis cause?
Pushes the membranes against the rigid cell walls = turgor
73
Effects of Osmosis on Plant Cells What happens as the turgor pressure increases?
It resists the entry of further water and the cell is said to be turgid
74
Effects of Osmosis on Plant Cells What happens when plant cells are placed in a solution with a lower water potential than their own?
Water is lost from the cells by osmosis
75
Effects of Osmosis on Plant Cells What does water lost from the cells by osmosis lead to?
Reduction in the volume of the cytoplasm
76
Effects of Osmosis on Plant Cells What does reduction in the volume of the cytoplasm cause?
Pulls the cell-surface membrane away from the cell wall - the cell is said to be plasmolysed
77
What forms a membrane?
A phospholipid bilayer
78
Where do cells normally exist?
In aqueous environments
79
What is the head of a phospholipid?
Charged hydrophilic head
80
What is the tail of a phospholipid?
Hydrophobic fatty acids tails
81
Who created the fluid-mosaic model and when?
1972 Singer and Nicholson
82
Why is it a FLUID mosaic model?
Because the phospholipid said are free to move within the layer relative to each other
83
What does fluidity give a membrane?
Flexibility
84
Why is it a fluid MOSAIC model?
Because the proteins embedded in the bilayer vary in shape, size and position
85
What do plasma membranes contain?
Various proteins and lipids - the type and number of which are particular to each cell
86
What important role do membrane proteins have?
the various functions of membranes
87
What type of membrane proteins are there?
Intrinsic and extrinsic proteins
88
Intrinsic Proteins Define integral proteins
Are transmembrane proteins that are embedded through both layers of a membrane
89
Intrinsic Proteins What do intrinsic proteins have?
Amino acid with hydrophobic R-groups on their external surfaces, which interact with the hydrophobic core of the membrane keeping them in place
90
Intrinsic proteins What do channel proteins provide?
A hydrophilic channel that allows passive movement of polar molecules and ions down a conc gradient through membranes
91
Intrinsic Proteins How are channel proteins held in position?
By interactions between the hydrophobic core of the membrane and the hydrophobic R-groups on the outside of the proteins
92
Intrinsic Proteins What do carrier proteins have a role in?
Both active and passive transport
93
Intrinsic Proteins What do carrier proteins often have to do?
Change shape
94
Intrinsic Proteins Where are glycoproteins found?
Embedded in the cell-surface membrane with attached carbohydrate chains
95
Intrinsic Proteins What role do glycoproteins play?
In cell adhesion and as receptors for chemical signals
96
Define cell adhesion
When cells join together to form tight junctions in certain tissues
97
Intrinsic Proteins What happens when chemicals bind to the receptor?
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
Give examples of cell signalling
- 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
Intrinsic Proteins How do Beta blockers work?
Act by binding to cell receptors and are used to reduce the response of the heart to stress
100
Intrinsic Proteins What are glycolipids similar to?
Glycoproteins
101
Intrinsic Proteins What are glycolipids?
Lipids with attached carbohydrate chains
102
Intrinsic Proteins What can glycolipids be called?
Cell markers / antigens
103
Intrinsic Proteins What is the role of glycolipids?
Be recognised by the cells of the immune system as self or non-self
104
Extrinsic proteins Where are extrinsic/peripheral proteins found?
Present in one side of the bilayer and can move between layers
105
Extrinsic proteins What do they normally have in their outer surface?
Hydrophilic R-groups
106
Extrinsic proteins What do they interact with?
With the polar heads of the phospholipids or with intrinsic proteins
107
Extrinsic proteins What is cholesterol?
A lipid with a hydrophilic and hydrophobic end that regulates the fluidity of a membrane
108
Extrinsic proteins Where are cholesterol molecules positioned?
Between phospholipids in a membrane bilayer
109
Extrinsic proteins What does cholesterol do to the bilayer?
Add stability without making then too rigid
110
Extrinsic proteins What does cholesterol prevent?
Membranes becoming too solid by stopping the phospholipid molecules from grouping too closely and crystallising
111
Membranes can be the site of…
Chemical reactions
112
Mark Scheme Points How does cholesterol affect fluidity?
- 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

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