2b Flashcards
what do membranes control
what passes through as they are partially permeable
what types of diffusion does cell membranes let happen
diffusion, osmosis and active transport
what are the jobs of the membrane
provide a barrier between enviroment and the inside
divide the cell into different compartments
controls what enter and leaves the cell
what is the fluid mosiac model
a model that suggested the arrangement of molecules in the membrane are phosopholipd molecules that form a bilayer.
why is it desribed as a fluid
the phosopholipids are constantly moving
why is it described as mosiac
proteins are scattered through the bilayer.
e.g the channel proteins and receptor proteins
what are the two parts of a phospholipid in the membrane
hydrophilic head- attracts water
hydrophobic tail - repels water
how does the phospholipid bilayer work
the heads face out towards the water/ enviroment
the tails face in
this is so the membrane doesnt allow water soluble substances though it
what does cholestrol do in the membrane
holds together each phospholipid so they are more tightly packed
desribe an experiment that allows you to test the permeability of the mebrane
1) use a scalpel to cut five equally sized pieces of beetroot
2) add the five pieces of beetroot to 5 test tubes and add 5cm3 of water using a pipette
3) place each test tube in a water bath of different temperature e.g 10, 20, 30 etc for a set amount of time
4)remove pieces of beetroot from test tubes leaving the coloured liquid
5) use a colourimeter to measure the absorbance of the liquid
the higher the absorbance the more colour pigment so higher permeablility of membrane
how does increasing temp increase membrane permeability
look in text book
what is simple diffusion
net movement of particle from an area of higher concentration to an area of lower concentration
what is the concentration gradient
the path from an area of higher concentration to an area of lower concentration
what kind of process is diffusion
passive process - no energy
what is the difference between simple diffusion and facilitated diffusion
facilitated diffusion uses carrier proteins and protein channels
why is facilitated diffusion used
it can transport larger molecules and charged particles through more quickly
how does a carrier protein work and what does it transport
it transport larger molecules
1) large molecule attaches to carrier protein
2) then the protein changes shape
3) this releases the molecule on the opposite side of the membrane
how does a channel protein work and what does it transport
it transports channel proteins
through normal diffusion
what does simple diffusion depend on
the concentration gradient
the thickness of the exchange surface
the surface area
how does microvilli increase diffusion rate
it increases SA
what does facilitated diffusion depend on
concentration gradient
number of channel or carrier proteins
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 of water molecules to diffuse out of or into a solution
what has the highest water potential
pure water
what is it called when 2 solution have the same water potential
isotonic
what does the rate of osmosis depend on
the water potential gradient
the thickness of the exchange surface
the surface area of the exchange surface
desribe how to do serial dilution
1) line up 5 test tubes in a rack
2) add 10cm3 of intial 2M sucrose solution to first test tube and 5cm3 of water to the others
3) then using a pipette draw 5cm3 of solution from the first add it to the water in second tube and mix
4) now repeat this on the next test tubes but half the volume of 2M sucrose
desribe the experiment to investigate the water potential of plant tissue
using the solutions you made
1) use a cork borer to cut potatoes into equally sized tubes
2) measure the mass of each of the potatoes
3) place one in each of your sucrose solutions
4) leave the chips in their for 20 minute
5) remove and gently pat dry then weigh the mass at end
6) work out the percentage change and draw a graph
what is active transport
the process of moving molecules or ions across a cell membrane against a concentration gradient
what 2 things make active transport different to facilitated diffusion
it goes from low to high
it requires energy atp
but it does use carrier proteins
what is ATP and what happens to it in active transport
it is a common energy source
it undergoes hydrolysis splitting it into ADP and Pi( inorganic phosphate) releasing energy
what are cotransporters and how do they work
they are a type of carrier protein
1) they bind to 2 molecules at a time
2) the concentration gradient of one of the molecules is used to move the other molecules against its own conc gradient
how does the sodium potassium pump work
=Binding of sodium ions: The pump protein binds to three sodium ions from the inside of the cell.
=ATP hydrolysis: An ATP molecule binds to the pump and is broken down into ADP and a phosphate group, providing energy for the conformational change.
Conformational change:
=The pump changes shape, releasing the sodium ions to the outside of the cell.
=Binding of potassium ions: The pump then binds to two potassium ions from the extracellular fluid.
=Return to original shape: The pump returns to its original shape, releasing the potassium ions into the cell and completing the cycle.
where does the sodium potassium pump work
in the small intestine in the illium
