Microscopes Flashcards
Why do we use microscopes?
viewing cells
increases size
see structures may not normally see
What is magnification?
number of times larger in real life
What is resolution?
the ability to distinguish between two different points
cell-surface membrane can be seen with transmission electron microscope but not optical - why?
higher resolution, therefore can distinguish more easily - shorter wave length
What is the possible magnification of an optical microscope?
2000x
What is the possible magnification of a transmission electron microscope?
10,000,000x
What is the possible magnification of a scanning electron microscope?
10,000,000x
What is the possible resolution of an optical microscope?
200nM
What is the possible resolution of a transmission electron microscope?
0.1nM
What is the possible resolution of a scanning electron microscope?
20nM
What is the method of focussing light in an optical microscope?
lenses
What is the method of focussing light in an electron microscope?
magnets
How is the specimen prepared in an optical microscope?
on slide with cover slip
can be living
How is the specimen prepared in an electron microscope?
dehydrated
stained with metal salts
mounted on a copper grid
placed in vacuum
can’t be living
Why are electron microscopes stained with metal salts?
causes electrons to scatter differently, giving contrast
What are the advantages of optical microscopes?
cheap
shows colour
What are the advantages of transmission electron microscopes?
high magnification and resolution
What are the advantages of scanning electron microscopes?
3D image
high magnification and resolution
What are the disadvantages of optical microscopes?
low resolution
staining needed for non-colour specimens
What are the disadvantages of transmission electron microscopes?
specimen dead
large equipment - training
vacuum needed
complex staining process
electron may destroy specimen
specimen must be very thin
What are the disadvantages of scanning electron microscopes?
specimen dead
large equipment - training
vacuum needed
complex staining process
electron may destroy specimen
What are the steps in cell fractionalisation?
homogenisation:
cells broken up by blender (homogensiser) to releases organelles from cell
resultant fluid is homogenate
Filter to remove large debris/whole cells
ultrafiltration:
separation of homogenate using centrifugal force in a centrifuge
How does centrifuge take place?
centrifuge at lower speed to separate cell fragments / heavy organelles
re-spin supernatant, after pellet removed, at higher speed to get smaller, light organelles
What is in the 1st pellet?
low speed
whole cells
nuclei
cytoskeletons
