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Biology aqa AS > cell membranes > Flashcards

cell membranes Flashcards

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1
Q

what are cell membranes

A

barriers between the cell and its environment, controlling which substances enter and leave.

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2
Q

permeability of cell membranes

A

partially permeable

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3
Q

what is partially permeable

A

allow some molecules through but not others

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4
Q

how can substances move across the cell membrane

A

diffusion, osmosis or active transport

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5
Q

membrane around organelle function

A

divide the cell into different compartments by acting as a barrier between organelle and cytoplasm, controlling what enters and leaves the organelle

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6
Q

cell membrane structure

A

lipids (mainly phospholipids), proteins and carbohydrates

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7
Q

arrangement of molecules in membrane

A

fluid mosaic structure

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8
Q

fluid mosaic structure

A

1) phospholipid molecules
2) cholesterol molecules
3) proteins

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9
Q

phospholipid in fluid mosaic structure

A

from a continous double layer (bilayer) that is constantly moving (fluid), some lipids have polysaccharide chain attached (glycolipid)

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10
Q

cholesterol molecules in fluid mosaic structure

A

are present

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11
Q

proteins in fluid mosaic structure

A

(channel protiens, carrier protiens - that allow large molecules and ions to pass through, recepter protiens - detect chemicals that cause the cell to respond, e.g hormone insulin binds to recepter proteins on liver cells which tells them to absorb glucose) are scattered (some move sideways, some are fixed) (some have polysaccharide chains attatched = glycoprotiens)

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12
Q

phospholipid in cell membrane role

A

forms a barrier for dissolved substances (hydrophilic head and hydrophobic tail form a bilayer with heads facing outwards on each side with tail on inside so water-soluble materials can’t pass through e.g ions)

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13
Q

cholesterol in cell membrane role

A

gives membrane stability (bind to tails of phospholipids so they pack more closely together so they become less fluid and more rigid, helping to maintain shape = important for cells without support)

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14
Q

investigating cell membrane permeability

A

1) use scalpel to cute 5 equally sized pieces of beetroot
2) rinse piece to remove and released pigment
3) place in 5 seperate test tubes containing 5cm3 of water (measured using pipette)
4) place in 5 water baths of different temperatures at 10 degree intervals for the same length of time (measured using stopwatch)
5) remove betroot pieces to leave coloured water
6) use colorimeter to test the clarity
7) recort results and draw a graph

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15
Q

what is a colorimeter

A

machine that passes light through a liquid and measures how much light is absorbed

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16
Q

temperature on membrane permeability

A

0>temperature>45 most permeable

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17
Q

temp below 0 on permeability

A

more permeable (channel protiens and carrier proteins deform, ice crystals may pierce the membrane)

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18
Q

temp 0-45 on permeability

A

increasing permeability (phospholipids have more energy so move more=moer gaps)

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19
Q

temp above 45 on permeability

A

more permeable (phospholipid layer melts, channel and carrier proteins deform, water inside cell expands which puts pressure on the membrane)

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20
Q

solvents on membrane permeability

A

increases permeability (solvent dissolves lipids which causes it to lose structure)

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21
Q

what is diffusion

A

passive process, movement of particles from an area of higher concentration to an area of lower concentration, until there is no longer a concentration (equilibrium) (e.g oxygen and CO2 across a cell membrane

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22
Q

what is a passive process

A

one that does not require energy

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23
Q

types of diffusion

A

simple and facilitated

24
Q

simple diffusion

A

molecules diffuse directly through a cell membrane from area of higher concentration to an area of lower concentration

25
Q

rate of simple diffusion factors (3)

A

concentration gradient, thickness of exchange surface, surface area to volume ratio

26
Q

concentration gradient on simple diffusion

A

higher concentration gradient = faster rate

27
Q

thickness of exchange surface on simple diffusion

A

thinner = faster rate (less far to travel)

28
Q

surface area to volume ration on simple diffusion

A

larger SA:V = faster rate

29
Q

facilitated diffusion

A

passive process, large or charged particles (ions) (that would diffuse too slowly through simple diffusion) diffuse through carrier/channel proteins down a concentration gradient

30
Q

facilitated diffusion through carrier proteins

A

1) large molecule attaches to carrier protein in the membrane
2) protein changes shape
3) molecule is released on the opposite side of the membrane

31
Q

facilitated diffusion through channel proteins

A

form pores in the membrane for charged particles to diffuse through down the concentration gradient

32
Q

rate of facilitated diffusion factors (2)

A

concentration gradient, number of carrier/channel proteins

33
Q

concentration gradient of facilitated diffusion

A

higher conc gradient = faster rate

34
Q

number of carrier/channel proteins on facilitated diffusion

A

greater number = faster rate

35
Q

what are aquarporins

A

special channel protein that allow facilitated diffusion of water

36
Q

calculating diffusion rate from graphs

A

straight line graph = finding gradient

curved graph = drawing tangent and finding the gradient

37
Q

what is osmosis

A

the diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential

38
Q

what is water potential

A

the potential (likelihood) of water molecules to diffuse out of or into a solution (pure water = highest water potential)

39
Q

what is isotonic

A

when 2 solutions have the same water potential

40
Q

rate of osmosis factors (3)

A

water potential gradient, thickness of exchange surface, surface area to volume ratio of exchange surface

41
Q

water potential gradient on osmosis

A

higher water potential gradient = faster rate

42
Q

thickness of exchange surface on osmosis

A

thinner exchange surface = faster rate

43
Q

surface area to volume ratio of exchange surface on osmosis

A

larger SA:V = faster rate

44
Q

investigation water potential

A

serial dilutions

45
Q

serial dilution method

A

1) line up 5 test tubes in a rach, and add 10cm3 of 2 M sucrose solution into the first test tube and 5cm3 of distilled water into the other 4
2) draw 5cm3 of the solution from first test tube and add to the second text tube
3) mix thoroughly
4) repeat process 3 times to create 5 solutions of 2M, 1M, 0.5M, 0.25M, 0.125M

46
Q

investigating water potential of potato cells

A

1)cut potatoes into identically sized chips
2)divide into groups of 3 and weigh each group (using a mass balance)
3)place one group into each sucrose solution and leave for at least 20 mins
4)remove and dry gently with paper towel
5)weigh each group and record results
6)calculate % change in each group and create a calibration curve
potato chips will gain water in solutions with a higher water potential
where it crosses x-axis = where it is isotonic

47
Q

what is active transport

A

the movement of substances (molecules and ions) usually against a concentration gradient with the use of energy using carrier proteins

48
Q

energy used for active transport

A

ATP (produced by hydrolysis into ADP and Pi)

49
Q

what are co-transports

A

type of carrier protein that bind 2 molecules at a time to move them against a concentration gradient (e.g sodium and glucose)

50
Q

factors affecting rate of active transport

A

speed of carrier proteins, number of carrier proteins, rate of respiration

51
Q

speed of carrier proteins on active transport

A

faster they work = faster rate

52
Q

number of carrier proteins on active transport

A

more proteins = faster rate

53
Q

rate of respiration on active transport

A

faster = faster rate (as more ATP is made)

54
Q

active transport of glucose

A

in mammaliam ileum

1) sodium ions are actively transported out into blood which creates a concentration gradient
2) therefore sodium ions diffuse into the cells via the sodium -glucose co-transporter proteins
3) co-transporter carries glucose with the sodium, so glucose concentration inside cell increases
4) therefore glucose diffuses out the cell by facilitated diffusion

55
Q

what is the ileum

A

the final part of the small intestine

Biology aqa AS (7 decks)

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