Module 2: Microscopy Flashcards
Name the 2 different lenses on a compound light microscope
State the role of each of these lenses
What does the configuration of these lenses allow , compared to a simple light microscope ? 2 things
the objective lense and the eye piece lens
objective lens-is placed near the specimen and produces a magnified image
eye piece lens-the specimen is observed through here
it allows for a much higher magnification and a reduced chromatic aberration
Name the 4 different types of sample preparation
dry mounting
wet mounting
squash slides
smear slides
Describe how a sample is prepared using a dry mount technique …
2 points
-specimens are solid and viewed whole or cut into very thin slices (sectioning)
-specimen placed on centre of the slide and a cover slip is placed over the sample
Describe how a sample is prepared using a wet mount technique …
2 points
-specimens are suspended in a liquid such as water or immersion oil
-cover slip placed at an angle
Describe how a sample is prepared using a squash slide and a smear slide
3 points for squash slides , including a point about which type of sample is best to be prepared in this way
2 points for smear slides
squash slide:
-wet mount is prepared
-a lens tissue is then used to gently press down the cover slip
-potential damage to the cover slip can be avoided by squashing the sample between 2 microscope slides , most useful if sample is soft
smear slide:
-edge of slide used to smear the sample , creating a thin and even coating on another slide
-cover slip placed over the sample
Describe how a sample is illuminated using a light microscope
make 2 points
What does this technique cause in terms of the image produced?
-state and describe 2 points
-its illuminated from below using a white light
-the sample is illuminated all at once
this means the images have low contrast as most cells don’t absorb much light
resolution is also limited due to the wavelength of light and diffraction of light as it passes through the sample
Diffraction is the …
bending of light as it passes close to the edge of an object
Magnification is …
how many times larger the image is than the actual size of the specimen
Resolution is the …
ability to distinguish between two close together objects/separate entities
Why is staining used in the preparation of slides?
What does this allow?
to increase the contrast between different components as they take up the stain to different degrees
the increased contrast allows components to become visible so they can be identified
What can differential staining achieve ?
2 points
-it can distinguish between two types of organism that would otherwise be hard to identify
-can also differentiate between different organelles of a single organism in a tissue sample
Name and describe the 2 main types of staining technique
(state what they do and the procedures used)
3 points about the procedure for each
gram staining-separates gram positive and gram negative bacteria
-done by applying crystal violet to specimen and adding iodine to fix the dye
-wash slide with alcohol
-gram positive will retain the stain but gram negative do not
acid fast-differentiates species of Mycobacterium from other bacteria
-carbolfuchsin dye carried into cells by a lipid solvent
-cells are washed with an acid/alcohol solution
-mycobacteria retain the dye but others don’t and are then exposed to a methylene blue stain
Describe how resolution can be increased …
What does this result in ?
by using beams of electrons which have a wavelength that is much shorter than light , therefore beams can be much closer together before they overlap
-this means much smaller/closer together objects can be seen separately
What do you use to measure the size of a sample under a microscope?
an eye piece graticule
What is an eye piece graticule?
make 2 more points about eye piece graticules
a glass disc that is marked with a fine scale of 1 to 100
the scale has no units so remains unchanged whichever objective lens is in place
the relative size of the divisions does increase with each increase in magnification
