staining Flashcards
define artefacts
an apparent structural detail that is caused by the processing of the specimen and is therefore not a legitimate feature of the specimen
examples of artefacts
bubbles
loss of continuity in membranes
distortion of organelles
empty spaces in cytoplasm
mesosomes
what is a dry mount
solid specimens viewed whole or cut into very thin slices
cover slip over specimen
e.g. hair, pollen, dust, insect parts, muscle, tissue, plants
what is a wet mount
specimen suspended in liquid (water/oil)
cover slip placed at an angle
e.g. aquatic samples and other living organisms
what is squash slides
a wet mount but the cover slip is pressed down
good for soft samples
e.g. root tip squashes –> look at cell division (careful not to damage the cover slip)
what are smear slides
edge of a slide is used to smear the sample creating a thin even coating on another slide
cover slip places over sample
e.g. blood smears to view blood cells
what is an eyepiece graticule
glass disc marked with fine scale of numbers but no units
what does a graticule enable you to do
what does a graticule enable you to do
define calibrate
to mark (a gauge or instrument) with standard scale of readings
what is a stage micrometer
a microscope slide with tiny ruler
why do we stain
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
what are positively charged dyes attracted to
negatively charged materials in cytoplasm
what do positively charged dyes stain
negatively charged materials in cytoplasm cell components
what is differential staining
distinguish between to types of organisms or different organelles within an organism that would otherwise be hard to identify
e.g. gram staining , acid-fast technique
what is gram stain technique
used to separate bacteria into gram positive and gram negative
based on thickness of cell wall
how does gram stain technique work
crystal violet stain is applied
iodine is applied, fixes the dye
washed with alcohol
cells with thick walls retain stain, appear blue ; cells with thinner walls lose the blue/purple stain
safranin dye is applied to gram negative, appear red
what is acid-fast technique used for
differentiate species of myobacterium from other bacteria
how does acid-fast technique work
a liquid solvent is used to carry carbolfuchsin dye into the cell being studied
cells are then washed with a dilute acid-alcohol solution
myobacterium (acid-fast) are not affected by the acid-alcohal and retain the carbolfuchsin stain (bright red)
other bacteria (non acid fast) lose the stain and are exposed to a methylene blue stain (blue)
