Microscopes Flashcards
Why do we use microscopes?
To view cells with an increase in size
What is magnification?
The number of times larger than in real life
What is the magnification of a light microscope?
2000x
Magnification of an electron microscope?
10,000,000x
What is the resolving power?
The ability to distinguish between 2 different objects/points
High resolution = what type of wavelength?
Short wavelength
What does a high resolution allow us to do?
Allows us to see internal structures and organelles e.g. cell membrane, mitochondria
What do all microscopes have?
A source of energy
Lenses for focussing
Sensor
What is the wavelength like for an electron microscope (TEM and SEM)?
0.004nm
What is the resolution for TEM?
0.1nm
What is the resolution for SEM?
20nm
What do TEM and SEM use to focus?
Magnets
What is the electron micrograph?
The image created on a screen or photographic paper
What does the specimen being dehydrated mean? (for a TEM)
The specimen is now dead
Why do we cut the specimen into thin slices?
We need the electrons and light to pan through
Why do we need to stain the metal ions?
Allows us to see them more easily
Does TEM pass through the sample or is it directed onto the sample?
Passes through the sample
Does SEM get passed through the sample or directed onto the sample?
Directed onto the sample
Is TEM a 2D image or 3D image?
2D image
Is SEM 3D or a 2D image?
3D
The darker the parts (TEM)?
The thicker the sample
Disadvantages of an electron microscope?
Expensive
Have to have specialist training to use them
Dead specimens- have to be dehydrated
Iodine?
Stains carbohydrates in plant and animal specimens brown or blue-black
Stains glycogen red
Methylene blue?
Stains acidic cell parts (like nucleus) blue. Use on animal, bacteria and blood specimens
Eosin Y?
Stains alkaline cell parts (like cytoplasm) pink. Use on plants, animals and blood
Toluidine blue?
Stains acidic cell parts (like nucleus) dark blue. Good to show mitosis in plant cells
Crystal violet?
Stains bacteria purple
Aceto-orcein?
Biological stain for chromosomes and connective tissue
Method of illuminating sample in light and TEM and SEM?
Light- light
Electron- TEM and SEM
Method of focussing waves?
Light- lenses
TEM and SEM- magnets
Can specimen be living?
Light- yes
TEM and SEM- no
How is the specimen prepared in light microscope?
Thin specimen on slide with a cover slip
How is the specimen prepared in TEM and SEM?
Fixed
Dehydrated
Stained using metal salts
Mounted on a copper grid
Placed in a vacuum
What types of stains are used and how do they highlight features?
Light- potential staining needed e.g. Acetic orcein
TEM and SEM- specimen are stained with metal salts- this causes electrons to scatter differently, giving contrast
Advantage of light microscopes?
Cheap
Advantage of TEM and SEM?
High magnification and resolution
Disadvantages of light microscope?
Low resolution
Staining needed for non-coloured specimens
Disadvantage of SEM?
Specimen dead
Large equipment training needed
Vacuum needed
Complex staining process
Electron may destroy specimen
Disadvantage of TEM?
SAME AS SEM
But also: specimen must be very thin
