using a microscope Flashcards
what are the key components of a light microscope
eyepiece lens
objective lens
stage
light source
coarse and fine focus
how do you prepare a liquid specimen slide
add a few drops of the specimen onto the slide using a pipette
cover the liquid with a coverslip and gently press down to remove air bubbles
how do you prepare a solid specimen slide
-Use scissors to cut a small sample of the tissue
-Peel away or cut a very thin layer of cells from the tissue sample to be placed on the slide
-The tissue needs to be thin so that the light from the microscope can pass through
-Apply a stain
-Gently place a coverslip on top and press down to remove any air bubbles
what are more advanced ways that solid specimens can be prepped.
- fixing the specimen using formaldehyde, dehydrating it using ethanol or impregnating it with paraffin then cutting thin slices using a microtome
- paraffin would then be removed and a stain is applied.
OR
freezing the specimen using co2 or liquid nitrogen and then cutting the specimens using a cryostat.
how do you use a light microscope
- always start with the low power objective lens to prevent damage and its is easier to find the specimen
- start with the stage lowest down
- use the coarse focus to get a clearer image
how can you take measurements of cells under a microscope?
eyepiece graticule and stage micrometre
what is a graticule
a small disc that has an engraved ruler which can be placed into the eyepiece of a microscope.
- it has no fixed units so it must be calibrated for the objective lens in use, this is done by a stage micrometre.
- the number of micrometres each graticule unit is worth can be worked out.
the stage micrometre and graticule is lined up.
what are the limitations of using a graticule.
-the size of cells or structures may appear inconsistent due to different specimen slides because samples will have been cut at different planes.
- light microscopes cannot view as much as other microscopes due to low mag
-preparation can alter the cells.
* incorrect calibration causes measurements to all be wrong.
why are some samples stained?
to increase contrast between different components and to make the specimen more visible.
how does sample staining work?
dyes absorb specific colours of light while reflecting others, making the structures that absorb the dye visible.
-certain tissues absorb certain dyes due to their chemical nature
what is differential staining?
using multiple dyes to ensure the different tissues within the specimen show up.
what is used to stain DNA
methylene blue
what is eosin used to stain
cell membranes
what are 2 other commonly used stains
toluidine blue and phloroglucinol (red/pink)
what is used to stain specimens in electron microscopy?
heavy metal compounds such as lead, osmium tetroxide and ruthenium tetroxide
why are electron microscopy specimens stained?
so that the electrons are absorbed.
- the stains cause tissues to show up black or different shades of grey
what is a biological drawing?
a line picture which shows specific features that have been observed in a specimen.
what are the guidelines for biological drawings?
-The drawing must have a title
-The magnification used should be stated
- sharp HB pencil should be used
-Lines should be clears ingle lines with no smudges
*NO SHADING
-The drawing should take up as much of the space on the page as possible
-Well-defined structures should be drawn
-The drawing should be made with proper proportions
-Label lines should not cross or have arrowheads
