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A-level Biology > 2.1.5 - Biological membranes > Flashcards

2.1.5 - Biological membranes Flashcards

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1
Q

What is the role of cell membranes within the cell ?

A
  • Act as a partially permeable barrier between the cell and its environment, between organelles and the cytoplasm and within organelles ( allowing different conditions to be maintained in organelles/ cell and separates two aqueous regions )
  • They are sites of chemical reactions
  • They are sites of cell communication ( signalling )
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2
Q

What is the structure of the cell surface membrane ( describe fluid mosaic model ) ?

A
  • The cell membrane is formed from a phospholipid bilayer ( two layers of phospholipids )
  • The hydrophilic phosphate heads form he outer layer while the hydrophobic fatty acid chains form the inner layer
  • The plasma membrane contains various proteins and lipids which are free to move in membrane
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3
Q

How does the phospholipid bilayer structure aid the function of the cell membrane ?

A
  • The outer and inner environments of the cell are typically aquatic
  • Since the hydrophilic phosphate heads are turned outward forming the outer layer, this enables them to interact with water
  • Since the hydrophobic fatty acid chains are turned inward forming a hydrophobic core, this enables cell membrane to act as a barrier between environments
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4
Q

Define the term ‘intrinsic proteins’ ?

A

Intrinsic proteins - Proteins that are embedded through both layers of membrane

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5
Q

Name examples of intrinsic proteins ?

A
  • Channel proteins
  • Carrier proteins
  • Glycoproteins
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6
Q

What is the role of channel proteins in the cell-surface membrane ?

A

Channel proteins provide hydrophilic channels allowing for the passive movement of polar molecules/ions through the cell-surface membrane

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7
Q

What is the role of carrier proteins in the cell-surface membrane ?

A

Carrier proteins allow for the passive and active transport of molecules by changing shape

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8
Q

Define the term ‘extrinsic proteins’ ?

A

Extrinsic proteins - Proteins present in one side of the bilayer

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9
Q

What are glycoproteins ?

A

They are intrinsic proteins embedded in the cell-surface membrane with attached carbohydrate chains

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10
Q

What is the role of glycoproteins in the cell membrane ?

A
  • They are important in cell adhesion
  • They act as receptors for chemical signalling ( when chemical binds to the receptor it elicits a response from the cell = cell communication/ signalling )
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11
Q

Explain how glycoproteins allow for the effects of drugs on cellS ?

A
  • Glycoproteins act as receptors for chemical signalling
  • This allows some drugs to act by binding to receptors
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12
Q

name examples of drugs that act by binding to receptors on cell-surface membrane ?

A

Beta blockers = They are used to reduce the response of the heart to stress

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13
Q

What are glycolipids ?

A

Lipids with attached carbohydrate chains

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14
Q

What is the role of glycolipids in the cell-surface membrane ?

A

They act as cell markers/ antigens which can be recognised by the cells immune system as self or non-self

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15
Q

What is cholesterol ?

A

A lipid with a hydrophilic and hydrophobic end

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16
Q

What is the role of cholesterol in the cell-surface membrane ?

A
  • Cholesterol regulates the fluidity of the cell-surface membrane
  • Cholesterol provides stability to the membrane
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17
Q

Explain how cholesterol provides stability to cell-surface membranes ?

A
  • Cholesterol’s hydrophilic end interacts with the hydrophilic phosphate heads and the cholesterol’s hydrophobic end interacts with the tails
  • This adds stability to membranes without making them too rigid
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18
Q

Explain how cholesterol prevents the cell-surface membrane from becoming too solid ?

A
  • The presence of cholesterol molecules stop phospholipid molecules grouping too closely together and crystallising
  • This prevents the cell membrane from becoming too solid
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19
Q

What are the factors affecting cell-surface membrane structure ?

A
  • Temperature
  • Solvents
  • pH
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20
Q

Explain the effect of temperature on cell membrane structure ?

A
  • As the temperature increases, phospholipid molecules have more kinetic energy and move faster
  • This makes the cell membrane to lose structure and become more fluid
  • the temperature will continue to increase until the cell membrane breaks down completely
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21
Q

Explain the effect of temperature on cell membrane permeability ?

A
  • Due to the increase in temperature, the cell membrane loses structure and becomes more fluid
  • this increases cell membrane permeability
  • As the temperature continues to increase, the channel and carrier proteins will denature decreasing the permeability of the cell membrane
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22
Q

Explain the effect of pH on cell membrane structure ?

A
  • A low or high pH causes change in the tertiary structure of proteins
  • This causes channel and carrier proteins inside the cell surface membrane to denature and no longer function
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23
Q

Explain the effect of pH on cell membrane permeability ?

A
  • Extreme pH change causes carrier/ channel proteins to denature
  • This leads to the cell surface membrane permeability to decrease since less molecules/ions can pass through cell surface membrane via facilitated diffusion
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24
Q

Explain the effect of solvents on cell membrane structure ?

A
  • Water is a poor solvent which is important in formation of cell membrane/ phospholipid bilayer
  • Water causes the hydrophobic tails to be orientated inward creating hydrophobic core and hydrophilic heads to be orientated outward
  • Organic solvents are often less polar or non-polar and will dissolve cell membrane
25
Q

Name examples of less polar solvents than water ?

A
  • Alcohols
26
Q

Explain the effect of solvents ( such as strong and weak alcohols ) on the structure of the cell membrane ?

A
  • Strong alcohols will dissolve cell membrane and destroy cells
  • Weaker alcohol molecules with enter the cell membrane and their presence between phospholipid layers will disrupt the cell
27
Q

Explain the effect of solvents on cell membrane permeability ?

A

When the cell membrane is disrupted, the cell membrane becomes more fluid and therefore more permeable

28
Q

Define the term ‘diffusion’ ?

A

Diffusion - The passive net movement of particles from a region of high concentration to a region of low concentration down the concentration gradient

29
Q

What is a passive process ?

A
  • A process that happens due to the kinetic energy of particles in a gas/ liquid
  • It does not require additional energy
30
Q

Name examples of passive processes ?

A
  • Diffusion
  • Osmosis
31
Q

What are the different factors affecting the rate of diffusion ?

A
  • Temperature
  • Concentration gradient
  • Surface area
  • Diffusion distance
32
Q

Explain the effect of diffusion distance on the rate of diffusion ?

A
  • As the diffusion distance decreases, there is less distance the particles need to move across
  • Therefore it takes less time to travel a shorter distance causing the rate of diffusion to increase
33
Q

Explain the effect of surface area on the rate of diffusion ?

A
  • If you increase the surface area, there is a greater area over which diffusion can occur
  • Therefore, more particles can move across in a shorter period of time = increasing rate of diffusion
34
Q

Explain the effect of temperature on the rate of diffusion ?

A
  • As the temperature increases, the kinetic energy of particles increases
  • This causes particles to move faster and means there is a greater net movement of particles = increased rate of diffusion
35
Q

Explain the effect of concentration gradient on the rate of diffusion ?

A
  • As you increase the concentration gradient, there is a steeper concentration gradient
  • This means there is a greater net movement of particles so faster rate of diffusion
36
Q

Define the term ‘simple diffusion’ ?

A

Simple diffusion - Diffusion in the absense of a barrier/ membrane

37
Q

Define the term ‘facilitated diffusion’ ?

A

Facilitated diffusion - Diffusion across a partially permeable membrane through transport proteins

38
Q

What is the movement of particles in facilitated diffusion determined by ?

A
  • Membranes with protein channels are selectively permeable
  • In facilitated diffusion, movement of molecules is determined by concentration gradient
39
Q

What else affects the rate of facilitated diffusion? Why ?

A
  • The number of channel proteins
  • As the number of channel proteins increases, the net movement of particles across the cell membrane increases as there are more channel proteins for molecules/ions to move through
  • This causes the rate of diffusion to increase
40
Q

Define the term ‘active transport’ ?

A

Active transport - The movement of molecules/ ions from a region of lower concentration to a region of higher concentration in and out of the cell

41
Q

What is an active process ?

A

A process that requires energy and carrier proteins to move molecules against the concentration gradient

42
Q

Name examples of an active process ?

A

Active transport

43
Q

Describe the process of active transport ?

A

1 ) the molecule/ion binds to receptors in the channel of the carrier protein on the outside of the cell
2 ) On the inside of the cell, ATP binds to the carrier protein and is hydrolysed into ADP and liberated phosphate
3 ) Binding of the phosphate molecule to the carrier protein causes the protein to change shape, opening to inside of cell
4 ) The molecule/ ion is released to the inside of the cell
5 ) The carrier protein returns to its original shape

44
Q

Define the term ‘bulk transport’ ?

A

Bulk transport - another type of active transport for large molecules ( enzymes, proteins… ) and whole cells( bacteria ) which are too large to move through channel/ carrier proteins

45
Q

What are the two types of bulk transport ?

A
  • Endocytosis ( A form of bulk trasnport where large molecules are transported into the cell )
  • Exocytosis ( A form of bulk trasnport where large molecules are transported out of the cell )
46
Q

What are the two types of endocytosis ?

A
  • Phagocytosis ( for solids )
  • Pinocytosis ( for liquids )
47
Q

Describe the process of endocytosis ?

A
  • cell-surface membrane invaginates/ bends inward when it comes in contact with material to be transported
  • membrane enfolds material until membrane fuses forming a vesicle
  • vesicles then pinches off and moves into the cytoplasm to transfer that material for further processing into the cell
48
Q

Describe the process of exocytosis ?

A
  • Vesicles formed by the Golgi apparatus move towards and fuse with the cell-surface membrane
  • Contents of vesicle are released outside cell
49
Q

What role does ATP play in active transport ?

A

ATP is required for movement of vesicles along the cytoskeleton, changing the shape of cells to engulf materials and fusion of cell membranes as vesicles form or as they meet the cell membrane

50
Q

Define the term ‘osmosis’ ?

A

Osmosis - The overall passive net movement of water molecules across a selectively permeable membrane from a region of high concentration to a region of low concentration down the concentration gradient

51
Q

Define the term ‘water potential’ ?

A

Water potential - The pressure exerted by water molecules as they collide with a membrane/ container

52
Q

What is hydrostatic pressure ?

A
  • The diffusion of water into a solution leads to an increased volume of this solution
  • In a closed system, this results in an increase in pressure which is hydrostatic pressure
53
Q

Explain what happens to an animal cell when placed in a hypotonic solution ?

A
  • Water potential of solution is high than water potential of cell
  • This causes water molecules to move into the cell via osmosis increasing hydrostatic pressure
  • The cell membrane cannot withstand the increased pressure
  • This causes cell to burst/ cytolysis
54
Q

Explain what happens to an animal cell when placed in a isotonic solution ?

A
  • The water potential of the solution is the same as the water potential of the cell
  • This causes water to move in and out of the cell at the same rate via osmosis
  • This leads to no change in pressure and therefore the cell does not change
55
Q

Explain what happens to an animal cell when placed in a hypertonic solution ?

A
  • The water potential of the solution is lower than the water potential of the cell
  • This causes water to leave the cell via osmosis decreasing the volume of cell
  • This causes the cell membrane to ‘puker’ and undergo crenation
  • Cell will shrink/ be crenated
56
Q

Explain what happens to an plant cell when placed in a hypotonic solution ?

A
  • Water potential of solution is high than water potential of cell
  • This causes water to move into the cell via osmosis
  • This leads to an increase in hydrostatic pressure which pushes the cell membrane against the cell wall creating turgor pressure
  • The cell becomes turgid
57
Q

Explain what happens to an plant cell when placed in a isotonic solution ?

A
  • The water potential of the solution is the same as the water potential of the cell
  • This causes water to move in and out of the cell at the same rate
  • This leads to no change in the cell
58
Q

Explain what happens to an plant cell when placed in a hypertonic solution ?

A
  • The water potential of the solution is lower than the water potential of the cell
  • This causes water to leave the cell via osmosis
  • This leads to a reduced volume of cytoplasm pulling cell- membrane away from cell wall
  • This causes the cell to become plasmolysed

A-level Biology (30 decks)

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