What is the role of lenses in microscopy?
Lenses focus either light or electrons to create a magnified image of a specimen.
Why is a specimen smaller than 200 nm not visible with a light microscope?
Anything smaller than 200 nm cannot interact with visible light.
What happens to the light rays when they hit the specimen?
They are reflected, refracted, or absorbed by the specimen.
What is the role of the ocular lens?
To recreate the image in the viewer's eye
What is meant by light rays being divergent?
It is spreading out
In a typical brightfield microscope (seen in the animation), at which point does magnification begin?
the objective lens
What is the total magnification of a specimen viewed with a 10x ocular lens and a 45x objective lens?
450%
A student is looking at a bacterial specimen using the oil immersion lens, but has forgotten to put immersion oil on the slide. The specimen will appear
somewhat fuzzy and have poor resolution.
What does resolution mean?
the ability of a microscope to distinguish fine details and differentiate between two very close objects
Which of the following statements comparing electron microscopy and light microscopy is FALSE?
Both the electron microscope and the light microscope use the same wavelengths for illumination.
If acid-fast bacteria are stained with the Gram stain, they will stain gram-negative.
False
The purpose of a mordant in the Gram stain is to
prevent the crystal violet from leaving the cells
Which of the following places the steps in the correct sequence?1-Staining2-Making a smear3-Fixing
2-3-1
You are performing a Gram stain on gram-positive bacteria and you stop after the addition of the first dye. What is the appearance of the bacteria at this point?
purple
Which step in the Gram stain is the critical step in differentiating gram-positive cells from gram-negative cells?
alcohol-acetone
Bacterial smears are fixed before staining to
affix the cells to the slide
In a completed Gram stain, gram-negative bacteria are colorless.
False
The Gram stain, acid-fast stain and endospore stain have the following in common:
are differential stains
In the Gram-staining procedure, the primary stain is
crystal violet
Gelatin is used as a solidifying agent in microbiological media since few bacteria can degrade it.
False
An isolated colony on a streak plate contains millions (or even billions) of identical cells all arising from one initial cell.
True