Basic components of living systems: microscopy Flashcards
what is resolution?
the smallest distance two objects can be seen apart
how does the light microscope work?
light is sent from a light source through a specimen. The objective lens produces a magnified image which is magnified again through the eyepiece lens.
Describe dry mount preperation
solid specimens which are cut into thin slices. The specimen is placed on the slide with a coverslip over it.
Describe wet mount preperation
specimens are suspended in water or an immersion oil. A cover slip is placed on from an angle
Describe squash slide preparation
A wet mount is prepared first, then a lens tissue is used to gently press down the cover slip
how is resolution related to wavelength?
the shorter the wavelength, the higher the resolution
How is crystal violet and methylene blue used to stain?
Crystal violet and methylene blue are positively charged dyes which are attracted to negatively charged materials in cytoplasm leading to staining
How is nigrosin and Congo red used to stain?
Nigrosin and Congo red are negatively charged and are repelled by the negatively charged cytosol. These dyes stay outside cells which makes the cell stand out
Describe the gram stain technique
This technique is used to separate gram positive and gram negative bacteria. Crystal violet is applied first, the iodine which fixes the dye. The slide is then washed with alcohol. The gram positive bacteria will retain the crystal violet stain and appear blue or purple. Gram negative bacteria will lose the dye and are then stained with safranin dye, which is called a counterstain. These bacteria will appear red. Gram negative bacteria have thinner cell walls.
Describe the acid-fast technique
This technique is used to differentiate species of mycobacterium from the bacteria. A lipid solvent is used to carry carbolfuchsin dye into the cells. The cells are then washed with a dilute acid-alcohol solution. Mycobacterium only retain the carbolfuchsin dye which is red.
What is a disadvantage of an electron microscope?
artefacts can be produced which are structures that are produced from the preparation process (electron beam)
TEM microscope
a beam of electrons is transmitted through a specimen and focused to produce an image. Resolution=0.5nm
SEM microscope
a beam of electrons is sent through the specimen and the reflected electrons are collected. 3D images are produced. Resolution=3-10nm
what is an artefact?
a visible structural detail caused by processing the specimen
why was the fluorescent microscope developed into the confocal microscope?
blurry images were produced therefore laser light and a pin hole was used.
