methods of studying cells 3.2.1 Flashcards
micrometre equivalent in metres
0.000001 10^-6
nanometre equivalent in metres
0.000000001 10 ^-9
what type of microscope gives a better resolution
electron
why does an electron microscope give a better resolution
the beam has a shorter wavelength
what is the resolution of a light microscope
200nm
what is the resolution of an electron microscope
0.1nm
magnification equation
image size = actual size x magnification
why do light microscopes have relatively poor magnification
due to the relatively long wavelength of light
what does the eyepiece lens do
magnifies and focuses the image
from the objective
onto the eye
what does the objective lens do
collects light passing through the specimen and produces a magnified image
what does the condenser lens do
focuses light onto the specimen
how does an electron microscope work
uses a beam of electrons
to give a high resolution
electrons have a negative charge
therefore can use electromagnetics
to focus the beam
why do electron microscopes require a vacuum
because electrons can be deflected or absorbed by molecules in the air
what are the 2 types of electron microscope
scanning and transmission
transmission electron microscope (6)
2D image
high resolving power
not in colour
thin specimens
complex stating process
slow
scanning electron microscope (3)
3D image
thin specimens not necessary
lower resolution power than TEM
light microscope (5)
living or dead specimens
colour image
quick and easy preparation
low resolving power
limited magnification
electron microscope (4)
high resolving power
dead specimens
black and white image
many produce artefacts
what is an artefact
things one can see down the microscope that are not part of the cell or specimen
eg dust, air bubbles, fingerprints
what is cell fractionation
process where cells are broken up and organelles are separated out
what are the two steps of cell fractionation (differential centrifugation)
1 homogenisation
2 ultracentrifugation
what are the 3 steps of homogenisation
1 cut tissue in cold isotonic buffer
2 tissue ground in blender to break open cells
3 homogenate is filtered
what is the purpose of the cold isotonic buffer
cold - reduces enzyme activity that might break down organelles
isotonic - prevents osmotic gain or loss (swelling or bursting)
buffer - maintains pH
ultracentrifugation method
1 suspension of homogenate is placed in a test tube and centrifuged
2 at slow speed large fragments collect at the bottom and smaller ones remain near the top in liquid called supernatant
3 the larger fragments (sediment pellets) are removed
4 supernatant is re-spun at a faster speed
order at which organelles form pellet
1 unbroken cells, nuclei, chloroplasts
2 mitochondria
3 ER, Golgi, lysosomes
