cell membranes

Question 1

what are cell membranes

Answer 1

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

Question 2

permeability of cell membranes

Answer 2

partially permeable

Question 3

what is partially permeable

Answer 3

allow some molecules through but not others

Question 4

how can substances move across the cell membrane

Answer 4

diffusion, osmosis or active transport

Question 5

membrane around organelle function

Answer 5

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

Question 6

cell membrane structure

Answer 6

lipids (mainly phospholipids), proteins and carbohydrates

Question 7

arrangement of molecules in membrane

Answer 7

fluid mosaic structure

Question 8

fluid mosaic structure

Answer 8

1) phospholipid molecules
2) cholesterol molecules
3) proteins

Question 9

phospholipid in fluid mosaic structure

Answer 9

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

Question 10

cholesterol molecules in fluid mosaic structure

Answer 10

are present

Question 11

proteins in fluid mosaic structure

Answer 11

(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)

Question 12

phospholipid in cell membrane role

Answer 12

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)

Question 13

cholesterol in cell membrane role

Answer 13

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)

Question 14

investigating cell membrane permeability

Answer 14

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

Question 15

what is a colorimeter

Answer 15

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

Question 16

temperature on membrane permeability

Answer 16

0>temperature>45 most permeable

Question 17

temp below 0 on permeability

Answer 17

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

Question 18

temp 0-45 on permeability

Answer 18

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

Question 19

temp above 45 on permeability

Answer 19

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

Question 20

solvents on membrane permeability

Answer 20

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

Question 21

what is diffusion

Answer 21

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

Question 22

what is a passive process

Answer 22

one that does not require energy

Question 23

types of diffusion

Answer 23

simple and facilitated

Question 24

simple diffusion

Answer 24

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

Question 25

rate of simple diffusion factors (3)

Answer 25

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

Question 26

concentration gradient on simple diffusion

Answer 26

higher concentration gradient = faster rate

Question 27

thickness of exchange surface on simple diffusion

Answer 27

thinner = faster rate (less far to travel)

Question 28

surface area to volume ration on simple diffusion

Answer 28

larger SA:V = faster rate

Question 29

facilitated diffusion

Answer 29

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

Question 30

facilitated diffusion through carrier proteins

Answer 30

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

Question 31

facilitated diffusion through channel proteins

Answer 31

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

Question 32

rate of facilitated diffusion factors (2)

Answer 32

concentration gradient, number of carrier/channel proteins

Question 33

concentration gradient of facilitated diffusion

Answer 33

higher conc gradient = faster rate

Question 34

number of carrier/channel proteins on facilitated diffusion

Answer 34

greater number = faster rate

Question 35

what are aquarporins

Answer 35

special channel protein that allow facilitated diffusion of water

Question 36

calculating diffusion rate from graphs

Answer 36

straight line graph = finding gradient | curved graph = drawing tangent and finding the gradient

Question 37

what is osmosis

Answer 37

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

Question 38

what is water potential

Answer 38

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

Question 39

what is isotonic

Answer 39

when 2 solutions have the same water potential

Question 40

rate of osmosis factors (3)

Answer 40

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

Question 41

water potential gradient on osmosis

Answer 41

higher water potential gradient = faster rate

Question 42

thickness of exchange surface on osmosis

Answer 42

thinner exchange surface = faster rate

Question 43

surface area to volume ratio of exchange surface on osmosis

Answer 43

larger SA:V = faster rate

Question 44

investigation water potential

Answer 44

serial dilutions

Question 45

serial dilution method

Answer 45

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

Question 46

investigating water potential of potato cells

Answer 46

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

Question 47

what is active transport

Answer 47

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

Question 48

energy used for active transport

Answer 48

ATP (produced by hydrolysis into ADP and Pi)

Question 49

what are co-transports

Answer 49

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

Question 50

factors affecting rate of active transport

Answer 50

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

Question 51

speed of carrier proteins on active transport

Answer 51

faster they work = faster rate

Question 52

number of carrier proteins on active transport

Answer 52

more proteins = faster rate

Question 53

rate of respiration on active transport

Answer 53

faster = faster rate (as more ATP is made)

Question 54

active transport of glucose

Answer 54

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

Question 55

what is the ileum

Answer 55

the final part of the small intestine