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Biology A level > Membranes > Flashcards

Membranes Flashcards

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1
Q

Roles of membranes within cells and at the surface of cells?

A

Plasma membranes:
Seperates cell contents from outside environment
Controls the passage of materials in and out of the cell
Recognition of other cells
Receptor sites for signalling molecules
Transmission of nerve impulses
Insulation of nerves

Inside cells:
Acts as a reaction surface
Acts as an intracellular transport system
Compartmentalises cells, isolating different chemical reactions
Can form vesicles to transport substances
Isolate potentially harmful enzymes eg. in lysosomes

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2
Q

What is compartmentalisation?

A

The formation of cellular compartments, within the cell

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3
Q

Why is compartmentalisation useful?

A

Different processes require different environments, eg ph

Provides extra membrane surface area for reactions

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4
Q

What is a partially permeable membrane?

A

Membrane which allows the passage of small molecules of water and certain solutes, but not large solute molecules

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5
Q

What is cell signalling?

A

Processes that lead to communication and coordination between cells. Hormones binding to their receptors is an example

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6
Q

What’s a phospholipid bilayer?

A

Glycerol bonded to 2 fatty acids and a phosphate (phospholipid), bonded in a 2 layer arrangement, phospholipid heads in at edges (hydrophilic), tails at centre (hydrophobic)

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7
Q

What is meant by “fluid”, and “mosaic” in the fluid mosaic model?

A

Fluid= Phospholipids free to move around relative to each other, giving membrane fluidity

Mosaic describes the patchwork of proteins in the membrane

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8
Q

What’s a glycoprotein?

A

A protein with carbohydrate molecules attached

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9
Q

Where do you find glycoproteins in the plasma membrane?

A

Projects from external side of membrane

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10
Q

Function of glycoproteins?

A

Receptors in cell signalling
Antigens in cell recognition
Cell adhesion- binding cells together
Attach to water to stabilise membrane

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11
Q

What is a phospholipid?

A

A molecule consisting of a glycerol molecule, 2 fatty acid molecules and a phosphate group covalently bonded together. Form the basis of cell membranes

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12
Q

Where do you find the phospholipids?

A

Bilayer of molecules

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13
Q

Function of phospholipid?

A

Acts as a partially permeable membrane

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14
Q

What is cholesterol?

A

A lipid molecule ( sterol) found in all cell membranes and involved in the synthesis of steroid hormones

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15
Q

Where do you find cholesterol in the membrane?

A

Fits in between tails of phospholipid in the bilayer

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16
Q

Function of cholesterol in the bilayer?

A

Regulates membrane fluidity by stabilising membrane

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17
Q

What’s a glycolipid?

A

A lipid with a carbohydrate molecule attached to it

intrinsic

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18
Q

Where do you find glycolipids in the membrane?

A

Projects from external surface of membrane

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19
Q

Function of a glycolipid?

A

Receptor in cell signalling
Antigen in cell recognition
Attaches to water to stabilise membrane

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20
Q

What’s a channel protein?

A

A protein pore that spans a membrane, through which very small ions and water soluble molecules may pass through
(hydrophilic)
(intrinsic)

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21
Q

What’s a carrier protein?

A

Protein found in membranes, which is capable of carrying a specific molecule or ion through the membrane by active transport
(intrinsic)

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22
Q

What are intrinsic/integral proteins?

A

Embedded through both layers of the membrane, Hydrophobic R groups keep them in place as they interact with hydrophobic core of membrane

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23
Q

What’s a receptor site?

A

Protein or glycoprotein molecules on cell surfaces, used for attachment of specific substances such as hormones or viruses

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24
Q

What is cell adhesion?

A

Process of cells interacting and attaching to a surface substrate or another cell mediated by interactions between the molecules of the cell surface

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25
Q

How does cholesterol regulate fluidity of the membrane?

A

At high temperatures stabalises membrane and raises it’s melting point

At low temperatures prevents phospholipids clustering together and stiffening

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26
Q

What are extrinsic proteins?

A

Are present in one side of the bilayer

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27
Q

Importance of membrane bound proteins?

A

Receptors in cell signalling
Antigens in cell recognition
Cell adhesion- binding cells together
Attach to water to stabilise membrane
Allows water molecules and small ions to pass through
Uses active transport to allow molecules into cell

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28
Q

Explain how the binding of a molecule to a membrane bound glycoprotein can cause effects within a cell?

A

Cells release signals by exocytosis eg hormones or neurotransmitters
Signalling molecule binds on to specific receptor molecules on plasma membrane of target cells
This triggers a response within the cell

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29
Q

How does temperature affect the cell membrane?

A

More thermal energy increases kinetic energy so phospholipids in membrane move faster
Membrane becomes more fluid and loses it’s structure, it will eventually break down completely
This loss of structure increases permeability, so more particles can cross
However channel and carrier proteins denatured at high temperatures, reducing permability

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30
Q

How does a solvent affect the cell membrane?

A

Many organic solvents less polar than water, eg alcohols
Less concentrated solvents enter membrane and disrupt it, making it more fluid and permeable
This means nerve transmissions don’t function as normal

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31
Q

Describe a method using a colorimeter to investigate the effect of temperature (or a solvent) on the permeability on cell membranes

A

Equal sized pieces of beetroot placed in distilled water
Heated at 10 degree intervals in a water bath, meaning different amount of red pigment released
Colorimeter then measures absorbency (higher temperature means more absorbency)

32
Q

What’s simple diffusion?

A

The movement of molecules from a region of high concentration of that molecule, to a region of low concentration of that molecule, down a concentration gradient. No energy from ATP required

33
Q

What’s facilitated diffusion?

A

The movement of molecules from a region of high concentration of that molecule, to a region of low concentration of that molecule, down a concentration gradient. Uses 2 types of intrinsic membrane proteins (channel and carrier). No energy from ATP required

34
Q

What’s osmosis?

A

The movement of water molecules from a region of high water potential, to a low water potential

35
Q

What’s active transport?

A

The movement of molecules or ions across a membrane in the opposite direction of the concentration gradient, this process uses intrinsic carrier proteins in the membrane as pumps. Energy input from ATP is required

36
Q

What is passive transport?

A

movement of bio chemicals and other atomic or molecular substances across cell membranes without need of energy input

37
Q

What is endocytosis?

A

The process of taking materials into a cell by surrounding them with part of the plasma membrane, which then pinches off to form a vesicle within the cell. This is an active process requiring ATP

38
Q

What is exocytosis?

A

The process of removing materials from the cell by fusing vesicles containing the material with the cell membrane

39
Q

What’s cytosis?

A

The movement of large quantities of materials in/out of the cell.

40
Q

What’s pinocytosis?

A

The process of endocytosis involving the bulk movement of liquids into a cell

41
Q

What’s phagocytosis?

A

The ingestion of bacteria or other material by phagocytes and amoeboid protozoans.

42
Q

How does a carrier protein work?

A

Molecule or ion being transported binds to receptors of the channel of the carrier protein outside the cell

On the inside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and Phosphate

Binding of the phosphate molecule to the protein changes it’s shape opening it up to the inside of the cell

Molecule or ion released into the cell

Phosphate molecule released from protein and bonds to ADP to form ATP

Protein returns to original shape

43
Q

How do channel proteins work?

A

They form aqueous pores across the membrane across the lipid bilayer, which allow certain solutes through to the other side of the membrane. Faster than carrier proteins

44
Q

Why is the structure of ATP Important in active transport?

A

It needs to be hydrolysed then the Phosphate needs to be able to bond to the specific protein

45
Q

Explain how substances can move across a membrane via simple diffusion?

A

It’s the net movement of particles from an area of high concentration to low, will continue until an equilibrium is reached (particles move in both directions equally)

Particles in liquid or gas have kinetic energy so they are constantly moving, the movement is random eventually they will form an equal distribution on each side of the membrane

They pass through lipid bilayer, examples are Oxygen, CO2, small molecules and lipid based molecules

46
Q

Why is it easier for oxygen molecules to pass through the membrane than water molecules?

A

Oxygen is non polar, so not repelled by the hydrophobic interior of the membrane, whilst water is polar so it is

47
Q

Why can steroid hormones easily pass through the membrane?

A

They are lipid soluble

48
Q

Why are ions only able to pass through channel proteins?

A

They are repelled by the hydrophobic interior of the membrane

49
Q

Describe an investigation on temperature affecting diffusion?

A

Agar cubes in different temperature water baths with phenolphthalein solution turning them pink, add sodium hydroxide, a higher temperature will increase the rate of diffusion (volume filled over time)

50
Q

Describe an investigation on surface area affecting diffusion?

A

Agar cubes with different surface area with phenolphthalein solution turning them pink, add sodium hydroxide, the larger the surface area means an increased the rate of diffusion (volume filled over time)

51
Q

Factors affecting diffusion?

A

Temperature
Surface area
Concentration difference
(thickness of membrane)

52
Q

What is a solvent?

A

A liquid that dissolves solids

53
Q

What is a solution?

A

A liquid with dissolved solids

54
Q

What’s a solute?

A

A solid that dissolves in a liquid

55
Q

Definition of water potential?

A

A measure of the ability of water molecules to move freely in a solution. Measures the potential for a solution to lose water- water moves from a solution with high water potential to one with lower water potential. Water potential is decreased by the presence of solutes

The pressure exerted by water molecules as they collide with the container

56
Q

What’s the symbol for water potential?

A

Ψ psi

57
Q

What is the water potential of pure water?

A

0, so every other value has to be negative

58
Q

What’s water potential measured in?

A

Kila Pascals

59
Q

What happens when there’s a higher water potential outside an animal cell?

A

Water enters cell, it swells and bursts

60
Q

What happens when there’s an equal water potential outside an animal cell?

A

Water constantly enters and leaves cell at equal rates, no change to cell

61
Q

What happens when there’s a lower water potential outside an animal cell?

A

Water leaves cell, cell shrinks

62
Q

What happens when there’s a higher water potential outside an plant cell?

A

Water enters cell, protoplast swells and becomes turgid

63
Q

What happens when there’s an equal water potential outside a plant cell?

A

Water constantly enters and leaves cell at equal rates, no change to cell

64
Q

What happens when there’s a lower water potential outside a plant cell?

A

Water leaves cell, plasmolysis occurs, protoplast pulled away from cell wall

65
Q

What is plasmolysis?

A

Detachment of the plasma membrane from the cell wall, as the cytoplasm shrinks as water is lost from a plant cell

66
Q

What’s the protoplasm?

A

the colourless material comprising the living part of a cell, including the cytoplasm, nucleus, and other organelles.

67
Q

What’s the protoplast?

A

the protoplasm of a living plant or bacterial cell whose cell wall has been removed.

68
Q

What is crenation?

A

State of animal cells when they have been immersed in a solution with lower water potential and have lost water by osmosis making them shrivelled

69
Q

What is turgid?

A

Describes a cell that is full of water due to the entry of water by osmosis, when the pressure of the cell wall prevents more water entering the cell is said to be turgid

70
Q

What’s cytolysis?

A

When a cell bursts due to excess water

71
Q

What’s haemolysis?

A

The rupturing of an animal cell surface membranes and subsequent release of their contents, occurs when an excess of water moves in by osmosis

72
Q

Experiment to investigate effects of different water potential solutions on plant/animal cells?

A

Place potato pieces in different concentrations of glucose solution and measure their percentage mass changes

The higher the concentration of the glucose solution, the more the mass of the potato will decrease, the less the concentration of the glucose solution, the more than will increase

Find where the solution is equal concentration, where it crosses the X axis

73
Q

Why do plant cells not burst by osmosis?

A

They have strong cellulose cell walls surrounding the cell surface membrane, when water enters by osmosis the increased hydrostatic pressure pushes the membrane against the rigid cell walls. This pressure against the cell wall is called turgor. As the turgor pressure increases, it resists the entry of further water, so the cell is said to be turgid

74
Q

What does having a solute in water do to it’s water potential?

A

Causes water to enter cell

75
Q

What does having a high water pressure in the cell do?

A

Opposes water coming in

76
Q

How do you calculate the overall water potential of a cell?

A

Ψ (kPa) = Ψ (solute) + Ψ (pressure)

Biology A level (19 decks)

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