Topic 3 - Microscopy and staining Flashcards
What is a simple microscope
its a microscope consisting of only one lens, they produce good images but not high magnification
What are compound microscopes
they have a eyepiece lens and then one or more additional lens, lights is also directed onto the specimen using a condenser lens
Why are light of shorter wavelengths used in microscopes (blue light)
Because it increases the resolving power at higher magnifications, so blue light is used
Why is immersion oil used
to increase resolution
How does immersion oil increase resolution
Because oil and glass have the same refractive indices and channels the light more directly into the lens improving resolution
Bright field Microscopy
specimens are stained with dyes to improve contrast
Dark field microscopy
allowing for image contrast without using stain, instead using light to backlight the specimen, causing it be silhouetted on a dark background
TEM
Emitted into vacuum, focused on specimen, electrons pass through. visualied on a phosphorous coated screen, specimens must be treated to enhance contrast, good for surface and internal structure detail
SEM
scans surface of specimen
how do dyes work
they contain a chromosphere with a ring structure that has an unbonded electron
Cationic dyes +
basic dyes with positive charge on the chromophore, bind to nucleic acid, proteins and cell membranes
Anionic dyes -
acidic dyes with negatively charge chromophore, bind to positively charge molecules
A simple stain
is where only one dye is used on the specimen, like methylene blue or crystal violet
Differential stains
two dyes are used for additional contrast
The gram stain
cells are fixed to plate - primary stain crystal violet - iodine is used to wash it off - acetone is used to remove some primary stain - counter stained with basic fuchsin
