cell membranes Flashcards
what are cell membranes
barriers between the cell and its environment, controlling which substances enter and leave.
permeability of cell membranes
partially permeable
what is partially permeable
allow some molecules through but not others
how can substances move across the cell membrane
diffusion, osmosis or active transport
membrane around organelle function
divide the cell into different compartments by acting as a barrier between organelle and cytoplasm, controlling what enters and leaves the organelle
cell membrane structure
lipids (mainly phospholipids), proteins and carbohydrates
arrangement of molecules in membrane
fluid mosaic structure
fluid mosaic structure
1) phospholipid molecules
2) cholesterol molecules
3) proteins
phospholipid in fluid mosaic structure
from a continous double layer (bilayer) that is constantly moving (fluid), some lipids have polysaccharide chain attached (glycolipid)
cholesterol molecules in fluid mosaic structure
are present
proteins in fluid mosaic structure
(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)
phospholipid in cell membrane role
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)
cholesterol in cell membrane role
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)
investigating cell membrane permeability
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
what is a colorimeter
machine that passes light through a liquid and measures how much light is absorbed
temperature on membrane permeability
0>temperature>45 most permeable
temp below 0 on permeability
more permeable (channel protiens and carrier proteins deform, ice crystals may pierce the membrane)
temp 0-45 on permeability
increasing permeability (phospholipids have more energy so move more=moer gaps)
temp above 45 on permeability
more permeable (phospholipid layer melts, channel and carrier proteins deform, water inside cell expands which puts pressure on the membrane)
solvents on membrane permeability
increases permeability (solvent dissolves lipids which causes it to lose structure)
what is diffusion
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
what is a passive process
one that does not require energy
types of diffusion
simple and facilitated
simple diffusion
molecules diffuse directly through a cell membrane from area of higher concentration to an area of lower concentration
rate of simple diffusion factors (3)
concentration gradient, thickness of exchange surface, surface area to volume ratio
concentration gradient on simple diffusion
higher concentration gradient = faster rate
thickness of exchange surface on simple diffusion
thinner = faster rate (less far to travel)
surface area to volume ration on simple diffusion
larger SA:V = faster rate
facilitated diffusion
passive process, large or charged particles (ions) (that would diffuse too slowly through simple diffusion) diffuse through carrier/channel proteins down a concentration gradient
facilitated diffusion through carrier proteins
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
facilitated diffusion through channel proteins
form pores in the membrane for charged particles to diffuse through down the concentration gradient
rate of facilitated diffusion factors (2)
concentration gradient, number of carrier/channel proteins
concentration gradient of facilitated diffusion
higher conc gradient = faster rate
number of carrier/channel proteins on facilitated diffusion
greater number = faster rate
what are aquarporins
special channel protein that allow facilitated diffusion of water
calculating diffusion rate from graphs
straight line graph = finding gradient
curved graph = drawing tangent and finding the gradient
what is osmosis
the diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential
what is water potential
the potential (likelihood) of water molecules to diffuse out of or into a solution (pure water = highest water potential)
what is isotonic
when 2 solutions have the same water potential
rate of osmosis factors (3)
water potential gradient, thickness of exchange surface, surface area to volume ratio of exchange surface
water potential gradient on osmosis
higher water potential gradient = faster rate
thickness of exchange surface on osmosis
thinner exchange surface = faster rate
surface area to volume ratio of exchange surface on osmosis
larger SA:V = faster rate
investigation water potential
serial dilutions
serial dilution method
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
investigating water potential of potato cells
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
what is active transport
the movement of substances (molecules and ions) usually against a concentration gradient with the use of energy using carrier proteins
energy used for active transport
ATP (produced by hydrolysis into ADP and Pi)
what are co-transports
type of carrier protein that bind 2 molecules at a time to move them against a concentration gradient (e.g sodium and glucose)
factors affecting rate of active transport
speed of carrier proteins, number of carrier proteins, rate of respiration
speed of carrier proteins on active transport
faster they work = faster rate
number of carrier proteins on active transport
more proteins = faster rate
rate of respiration on active transport
faster = faster rate (as more ATP is made)
active transport of glucose
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
what is the ileum
the final part of the small intestine
