microscopy Flashcards
What are the four types of sample preparation for light microscopes?
- Dry mount
- Wet mount
- Smear slide
- Squash slide
What is a dry mount?
When thin slices or whole specimens are viewed, with just a coverslip placed on top.
What is a wet mount?
- When the specimens are added to water or a stain before the coverslip is lowered on with a mounted needle.
- can be used to observe aquatic organims
What is a smear slide?
- a smear slide is created by placing a drop of the sample at one end of the slide and using the edge of another slide to smear it across.
- can be used to view blood cells
what is squash slide?
- wet mounts, but you also push down on the coverslip to squash the sample.
- this is so it is thin enough for light to pass through.
- is used for viewing chromosomes in mitosis.
how do electron microscopes work? what can they produce? (generally)
Electron microscopes:
- The image is created using an electromagent to focus the bean of negatively charged electrons
- the beam of electrons has a very short wavelength- so a high resolution.
- EM must be in a vacuum so only non-living species can be examined
- the image is black and white as the sample must be stained.
how does a TEM work?
TEM:
- Extremely thin specimen stained and put in vaccum.
- Electron gun produces a beam of electrons that will pass through the specimen.
- some parts of the specimen absorb the electrons and this makes them appear darker
- produces a 2D image where you are able to see the internal structure of cells.
how does a SEM work?
SEM:
- Specimen doesnt need to be thin
- Electrons are beamed onto the surface and the electrons are scattered in different ways, depending on the contours of the specimen.
- produces a 3D image of the surface of the specimen.
how does a laser scanning confocal microscope work?
Laser scanning confocal:
- type of flourescent microscope
- uses a high light intensity to illuminate the specimin in a flourescent dye
- the microscope scans the specimen point by point using a focused laser beam to create a 2D or 3D image.
- can produce a 3D image where you can also see tiny structures that would be hard to section off
what is the resolution of a light, scanning electron, and transmission electron microscope
- LM- 200 nm
- SEM- 3-10 nm
- TEM- 0.2-0.5 nm
what is the magnification of a light, scanning electron and transmission electron microscope?
- LM- 1500-2000 x
- SEM- 100,000 to 500,000 x
- TEM- 500,000 to 2 million x
what are the rules for scientific drawings?
- draw in pencil.
- title of the diagram has to indicate what the specimen is.
- must state the magnification
- must label the key features
- must annotate cell components, cells, and sections of the tissue visible. This must state what colour and shapes they are and not their functions.
- only use solid lines that do not overlap
- no colouring or shading
- label lines must be horizontal, drawn with a pencil and ruler and not have arrowheads on them.
what is the gram staining technique?
- is used to separate bacteria into 2 groups
> gram- positive bacteria and gram- negative bacteria
PROCESS
- crystal violet is applied to the specimen, then iodine to fix it in place
- the slide is washed with alchohol
- gram-negative bacteria have thin walls and will lose the stain. These will then be stained with safranin dye (a counterstain)
- this makes gram-negative bacteria appear red.
- gram- positive bacteria will appear blue or violet.
what are the positively charged dyes and how do they work?
- crystal violet
- methylene blue
- they are attracted to negatively charged materials in the cytoplasm
what are the negatively charged dyes and how do they work?
- nigrosin
- congo red
- they are repelled by negatively charged cytosol
- the dyes therefore stay outside the cell so the cell interior contrasts with the background
