Biology - 2.1.3 - methods of studying cells
what is cell fractionation
separation of organelles due to their size and mass
what are the necessary environmental conditions needed for cell fractionation?
Buffer solution has a neutral pH to prevent cells from denaturing.
Buffer solution has same water potential as cell sample to prevent water moving in via osmosis - isotonic solution
Cold temperature to keep organelles from being damaged by enzyme activity
what is the first stage of cell fractionation?
homogenisation of cells using a device in a buffer solution. done to break open cells and allow organelles to escape
what is produced after homogenisation?
a cell homogenate, which is a solution containing organelles found in the cell
what is the second step of cell fractionation
filter to remove broken cells, unbroken cells and cell membranes
what is the third step of cell fractionation?
ultracentrifugation, sample is spun at a low speed at first to separate the heaviest organelle, which experiences a greater force.
After spinning, a nuclei pellet is formed, Th rest of the organelles are suspended in the supernatant
what is done with the supernatant after first spinning
poured into another test tube, spun at a higher speed to separate mitochondria
what is the order of mass of organelles
nucleus, mitochondria, lysosomes, ribosomes
what is the conversion from millimetres to micrometers
x1000
what is the conversion from micrometres to millimetres
/1000
what is the conversion of micrometres to nanometres
x1000
what is the conversion from nanometres to micrometers
/1000
what is the advantage of using a light microscope
they may be used on living samples to explore cellular processes
what is the disadvantage of using a light microscope
it has the lowest resolution of all other types
define resolution
the minimum distance between 2 objects where they can still be seen as 2 separate objects
why do light microscopes have a low resolution
wavelength of light is 400-700nm. If two objects are closer than 200nm, they are not distinguished as two separate objects
what is the equation for magnification
image size/ object size
what is the advantage of using a TEM
has the highest resolving power of all microscopes
what is the disadvantage of using a TEM
samples must be dead
2d images produced only
how does an transmission electron microscope work?
electron gun produces a beam of electron which passes down the inside of the microscope, without bouncing off of air molecules. they can be focused using magnets called electromagnetic lenses. sample is placed in path of electron beam. can pass through some sections easier than others
how does a scanning electron microscope work
uses beams of electrons to scan sections in a sample. Beam does not pass through the specimen, but instead electrons are scattered from the surface and detected.
what is the advantage of using an SEM
generates 3D images
what is the disadvantage of using an SEM
lower resolving power compared to TEM
what is an artefact
an incorrect image caused by the stain or microscope