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A-level Biology > Cell Membranes And Transport > Flashcards

Cell Membranes And Transport Flashcards

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1
Q

Role of fluid mosaic membrane

A
  • allows movement of substances between cells and their surroundings e.g. nutrients and waste products
  • allows cells to communicate with each other by cell signalling
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2
Q

Fluid

A
  • Phospholipids can move within their monolayer by diffusion
  • cholesterol maintains fluidity
  • unsaturated fatty acids form ‘kinks’, increases fluidity as phospholipids don’t fit closely together
  • the longer the fatty acid tail, the less fluid membrane
  • as temp increases, fluidity of the membrane increases
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3
Q

Mosaic

A

When viewed through an electron microscope , the proteins (carrier/channel/glycoproteins) are scattered throughout the bilayer.

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4
Q

The cell surface membrane of phospholipids is…

A

A bilayer

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5
Q

Which direction do the tails of the fatty acids face?

A

Hydrophobic - inwards, away from aqueous environment

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6
Q

Which direction do the phosphate heads face?

A

Hydrophillic - faces aqueous environment

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7
Q

Phospholipids

A

Fatty acid:
- barrier to water soluble compounds/ions
- non-polar, allows passage of lipid soluble substances
- hydrophobic interactions with integral proteins
- structure of fatty acid tails maintains fluidity

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8
Q

Phospholipids can be…
When they…

A
  • Some phospholipids are chemically modified to act as signaling molecules
  • when they more between their belayer they activate other molecules e.g. Enzymes
  • OR can get hydroysed to release small, water-soluble, glycerol containing molecules which can then diffuse through the cytoplasm and bird to specific receptors
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9
Q

Phosphate head

A
  • Polar
  • regulates finality stability
  • storage
  • restricts movement of phospholipids
  • influences permeability of membrane
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10
Q

Cholesterol

A
  • Contain hydrophilic heads and hydrophobic tails
  • present in animals, less in plants
  • not present in prokaryotes
  • maintains finality of membrane
  • prevents membrane from rupturing
  • prevents membrane from being too rigid or fluid
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11
Q

At low temps cholesterol…

A

Increases fmidity of the membrane
- bc prevents close-packing of the phospholipid tails
- increased fluidity enables cells to survive cold temps

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12
Q

At higher temps cholesterol…

A

Prevents membrane from becoming too fluid as there is increased interaction of the phossphelipid tails with the cholesterol molecule
- enables cells to became more stabilised

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13
Q

Cholesterol and stability in cells

A

Provide mechanical stability
- without cholesterol membranes quickly break and the cells burst open

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14
Q
  • What does cholesterol prevent?
A

prevents polar substances (e.g. ions) from leaking through the membrane due to hydrophobic regions
Prevents membrane being too rigid/fluid

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15
Q

*How are phospholipids able to move within their monolayer

A

Diffusion

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16
Q

*what does cholesterol do

A

Maintains fluidity

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17
Q

*what do unsaturated fatty acids form

A

Kinks —> increase fluidity as phospholipid don’t fit closely together

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18
Q

*what does a longer fatty acid tail mean

A

Decrease fluidity of the membrane

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19
Q

*how does fluidity change with temperature

A

Increase temperature = increased fluidity

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20
Q

*what are phospholipids a barrier to

A

Water soluble compounds (non-polar)

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21
Q

*what do phospholipids allow the passage of

A

Lipid soluble substances

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22
Q

*what does the structure of fatty acid tail do

A

Maintains fluidity

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23
Q

*what type of proteins do hydrophobic interactions have

A

Integral proteins

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24
Q

*phosphaste head polar or non-polar

A

Polar

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25
Q

*what does a phosphate head do/used for

A

Regulates fluidity/stability
Storage

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26
Q

*what do phosphate heads restrict

A

Movement of phospholipids

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27
Q

*what do phosphate heads influence

A

Permeability of membrane

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28
Q

*what does cholesterol contain

A

Hydrophilic heads, hydrophobic tails

29
Q

*what organisms is cholesterol present in

A

Animals
Less in plants
None in prokaryotes

30
Q

*what does cholesterol do at lower temperatures

A

Increase fluidity of membrane —> prevents close packing of phospholipid tails

31
Q

*what does cholesterol do at higher temperatures

A

Prevents membrane becoming too fluid —> bc of increased interactions of phospholipid tails with the cholesterol molecule
- cells more stabilised

32
Q

*what kind of stability is effected by cholesterol

A

Mechanical stability - without cholesterol, membranes quickly break and burst open

33
Q

Glycoproteins

A
  • receptors for hormones/neurotransmitters
  • cell surface antigens for cell recognition
  • stabilise membrane structure by forming H bonds with water molecules
  • helps cells adhere together
34
Q

Glycolipids

A
  • cell surface antigens for recognition
35
Q

Transport proteins

A
36
Q

Channel proteins

A
  • allow facilitated diffusion - high to low concentration
  • most are gated
  • fixed shape
37
Q

Carrier proteins

A
  • flip between two shapes
  • binding site open at one side of membrane then the other
  • facilitated diffusion and active transport - against concentration gradient
38
Q

How is the rate of facilitated diffusion affected

A

By the number of channel or carrier proteins in the membrane
Whether proteins are open or closed

39
Q

Where are peripheral proteins located
E.g.

A

Inner or outer surface of membrane
E.g. enzymes, ATP synthesis in chloroplasts and mitochondria

40
Q

What are proteins on the inside of the CSM attached to
What do they do

A

cytoskeleton —> System of protein filaments
Help maintain and decide the shape of the cell, may be involved in changes of shape when cell moves

41
Q

What do the proteins on the inside of the CSM act as

A

Energy transducers

42
Q

Cell signalling

A

The molecular mechanism by which cells detect and respond to external stimuli, including communication between cells

43
Q

Why does cell signalling occur

A

So the organism is able to respond appropriately to its environment

44
Q

Cell signalling process

A
  1. Stimulus/signal is present
  2. Cell secretes a specific chemical - ligand
  3. Ligand transported by blood then binds to specific receptor of target cell
  4. Receptor goes through a *conformational change**
  5. Series of chemical reactions inside cell are triggered
  6. response occurs
45
Q

How to calculate SA:V

A

SA/V (unit 3)

46
Q

Facilitated diffusion

A
  • diffusion taking place though carrier/channel proteins
  • movement of polar molecules/ions moving from a region of high to low concentration
  • passive and random process
47
Q

What type of process is facilitated diffusion

A

passive and random process

48
Q

Active transport

A
49
Q

Osmosis

A

The movement of water molecules form a region of high to low water potential through a semi-permeable membrane, down a water potential/concentration gradient

50
Q

Why does osmosis occur

A

Due to random movement of water molecules

51
Q

Water potential equation

A

Water potential = solute potential + pressure potential

52
Q

What is water potential

A

The pressure created by water molecules to move

53
Q

Water potential of pure water

A

Zero - hypotonic solution

54
Q

What happens to water potential when a solute is added to pure water

A

More negative water potential - hypertonic
(Solute potential always has a negative value)

55
Q

Pressure potential is usually

A

0

56
Q

When will pressure potential have a positive value

A

When a plant cell is turgid and water molecules are exerting pressure on the cell wall

57
Q

Isotonic solution

A

When both solutions have the same concentration of solutes

58
Q

Describe the movement of water from a hypotonic solution to a hypertonic solution

A

Net movement of water

59
Q

osmosis in animal cells
What happens when:
1. Water potential of the surrounding solution is higher than that of the RBC
2. Water potential of the surrounding solution is lower than that of the RBC

A
  1. Water will enter the RBC and it will burst
  2. Water will leave the RBC and it will shrink - crinkled, cell solution becomes more concentrated
60
Q

How is the round shape of a RBC maintained

A

When in an isotonic solution

61
Q

Describe the net flow of water when:
1. The external water potential is less negative than the wp of the cell
2. The external wp is the sam as the wp of the cell
3. The external wp is more negative than the wp of the cell

A
  1. Net inflow of water
  2. No net water movement
  3. Net outflow of water
62
Q

Describe osmosis in plant cells

A
  • if wp is higher than the plant - water enters plant so become turgid good due to presence of cellulose cell wall (pressure potential positive)
  • if wp of surrounding solution is lower than the plant cell - plant becomes plasmolysed
63
Q

How to determine the wp of an unknown solution

A
  • place onion cells in a range of sucrose solutions (e.g. every 0.5)
  • count plasmolysed cells using microscope
  • plot graph of no. plasmolysed cells against concentration of solutions
  • place onion tissue in unknown solution
  • count no. plasmolysed cells
  • use graph p to determine concentration of unknown solution by extrapolation
64
Q

Bulk transport

A

Movement of large molecules e.g. proteins/polysaccarides, in and out of cells
(endo and exocytosis)
ATP is needed

65
Q

Exocytosis process

A
  • vesicle/vacuole moves towards CSM
  • fusion of vesicle with membrane - both contain phospholipids
  • contents secreted/released
  • active process - need ATP
66
Q

Endocytosis process

A
  • Vesicle containing molecule/molecule moves towards CSM
  • membrane engulfs molecule inwards
  • membrane is pinched off
67
Q

Pinocytosis
What is needed

A

The uptake of bulk liquids
ATP

68
Q

Importance of the cell surface membrane

A

A-level Biology (10 decks)

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