Microbio Lab 2 Flashcards
phase-contrast microscope
a microscope that is able to differentiate the transparent protoplasmic structures and enhance the contrast between a cell and its surroundings, without the necessity of staining; good for viewing live cells and motility
phase shift
as light passes through transparent objects and is slowed down by 1/4 wavelength
direct rays
rays that pass straight through unaffected by medium
diffracted rays
rays that are bent because they are retarded by the medium (due to density differences)
coincidence
if direct and diffracted light waves are brought into exact phase with each other; increased brightness
interference
if two light waves of equal amplitude are in reverse phase (1/2 off) and their amplitudes cancel each other to produce a dark object
annular stop
structure in diaphragm that allows only a hollow cone of light rays to pass through the condenser to the specimen on the slide
bright-phase microscopy
brighter image (amplitude summation)
dark-phase microscopy
darker image (amplitude interference or reverse phase)
ocular micrometer
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stage micrometer
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aseptic technique
ensures that no contaminating organisms are introduced into culture materials during handling or inoculation; also ensures that the organisms that are being handled do not contaminate the handler or others who may be present; its use means that no contamination remains are you have worked with cultures
Staining of cells is often performed to enhance images acquired by brightfield microscopy. Phase-contrast microscopy does not require cell staining. Why is this advantageous?
The movement of the cells and their activities cannot be viewed if the cells are stained since cell staining results in cell death.
As ligh passes through a transparent object, how are direct and diffracted light rays produced? How much phase shift occurs?
- Direct rays-unaffected with No phase shift
- Diffracted rays- bend and have a phase shift of 1/4 wavelength.
How do coincidence and interference of light rays differ? Which type of image does each produce?
Coincidence- Produces a brighter image
Interference- Produces a darker image
Differentiate between bright-phase and dark-phase microscopy in terms of phase shift.
Bright phase-a brighter image (amplitude summation)
Dark phase- a darker image (amplitude interference)
Which two items can be used to check the alignment of the annulus and phase ring?
centering telescope and Optovar.
A phase-contrast microscope differs from a brightfield microscope by having a _
- Diaphragm with an annular stop
- Phase plate in the objective lens
What would be best observed or a bacterial cell using phase-contrast microscopy?
A motility of cells
Amplitude summation occurs in phase-contrast optics when both direct and diffracted rays are _
in phase
The phase-contrast microscope is best suited for observing _
Living organisms on a slide with a cover glass
Where should a label be written on an agar plate?
on the bottom
How should agar plates be incubated
Upside down to prevent condensation on the agar
Disinfectants are effective against which types of organisms?
Disinfectants are effective against vegetative cells and viruses but not endospores
