Microscopy Flashcards
Why are light microscopes good
You can view living organisms
How does a light microscope work
A compound light microscope has two lenses- objective and eyepiece. Objective lens is near specimen, eyepiece lens is where the specimen is viewed. Objective lens produces a magnified image, which is magnified again by the eyepiece lens.
What’s the benefit of having two lenses in a microscope
Allows for much higher magnification and reduced chromatic aberration.
How do you prepare a dry mount sample
Solid specimens cut into thin slices- sectioning. Specimen placed on centre of slide and cover slip placed over the sample. Can also view sample whole.
How do you prepare a wet mount sample
Specimen suspended in water, cover slip placed on from angle. Aquatic samples or other living organisms can be viewed this way.
How do you prepare squash slides
Wet mount first prepare, lens tissue used to gently press down cover slip. Potential damage to cover slip can be avoided by squashing the sample between two microscope slides.
How do you prepare smear slides
Edge of slide is used to smear sample, creating a thin, even coating on another slide, cover slip placed over sample.
Why do you need stains
Stains increase contrast as different components within a cell take up stains to different degrees. The increase in contrast allows components to become visible so they can be identified.
How do you prepare a sample for staining
First placed on slide and allowed to air dry. This is then heat-fixed by passing through a flame. Specimen will adhere to microscope slide and take up stains.
What are the positively charged dyes
Crystal violet or methylene blue are positively charged dyes, which are attracted to negatively charged materials in cytoplasm leading to staining of cell components.
What are the negatively charged dyes
Nigrosin or Congo red are negatively charged and are repelled by the negatively charged cytosol. These dyes stay outside the cell, leaving cells unstained, which then stand out against the stained background.
What are gram stain techniques
Separates bacteria into two groups- gram positive and gram negative.
How do you test for gram positive bacteria
Crystal violet applied to to bacteria specimen on slide, then iodine which fixes dye. Slide is then washed with alcohol. Gram positive bacteria retain the crystal violet stain and will appear blue or purple under a microscope.
How do you test for gram negative bacteria
Gram negative bacteria have thinner cell walls and therefore lose crystal violet stain. They are stained with safranin dye- counterstain. These bacteria appear red.
What are gram positive bacteria susceptible to
Penicillin- Gram negative bacteria have much thinner cell walls which are not susceptible to penicillin.
