CH2 Flashcards
objective X ocular
total magnification
ability to distinguish between two objects
limited resolving resolution
why use blue light (400-500 nm)?
- shortest wavelength
- to optimize resolution
Abbe’s equation for resolution
d= 0.5 λ / s sin Θ
light must pass between two objects for them to be seen as separate
λ
refractive index (light bending properties)
n
n of air and oil
air = 1.0 oil= 1.5
-visible light, glass lenses
-magnification: 1000x to 2000x
-resolving power: use immersion oil and blue light
=0.2μm (200nm)
light microscope
- e- beam, electromagnetic lenses (
-magnification: over 100,000x
-resolving power: e- beam (λ =.005nm)
=0.5nm
electron microscope
- dark image against brighter background
- cheap and easy to use
- poor, contrast, MOs transparent, staining skills
bright field- light microscope
- light image and background dark
- useful for motile living organisms
- cheap and fairly easy to use
- good contrast without staining
- anything living or not will appear (debris)
dark field- light microscope
- slight difference in thickness/density converted to variations in light intensity
- useful for living MOs, some internal structures
- more expensive/ more difficult to use
phase contrast- light microscope
Which would have better resolution red (620nm) or green (550nm)?
green bc shorter λ
- stain specific cell/components with fluorescent dye
- expose specimen to short λ light (UV, violet)
- view the longer λ fluorescent light
- background dark, MOs fluorescent
- specificity with antibodies linked dyes
fluorescent- light microscope
- e- beam passes through specimen
- view internal cell structures
- requires very thin sections/slices, cut with glass or diamond knife
- staining (heavy metals)
transmission e- microscope TEM
- e- beam scans the surface of microbe (scattered e- collected)
- provide 3-D view of surface (internal not shown)
- easier prep
scanning e- microscope SEM
preserve/stabilize, kill, adhere, take up stain
fixation (heat/chemical)
two types of dyes
acidic and basic
colored ion
chromophore
chromophore +ive charge
basic dye
charge of most MOs
-
chromophore -ive charge and stains background
acidic dye
color with simple dye; size shape arrangement
simple staining
more than one dye so cells and structures are better to view
differential staining
outline the steps in gram staining
- crystal violet (primary stain) for 1 minute, water rinse
- iodine (mordant) for 1 minute, water rinse
- alcohol (decolorizer) fro 10.30 seconds, water rinse
- Safranin (counterstain) for 30-60 seconds, water rinse, blot dry
- gram stain will be ______ from _____
red, safranin
+ gram stain will be ______ from ______
purple, primary stain
what color are all gram stains at first?
purple
Christian Gram placed bacteria in one of 2 groups, what are they?
Gram - and Gram +
what two things will not stain?
endospores and mycobacteria
why can old cultures be variable for gram staining?
old + stain can lose color and look like - stain
Select all that are characteristics of transmission electron microscopes.
- Highest practical magnification over 100,000 times.
- Uses visible light for radiation source.
- Contains glass lenses.
- Uses electron beam for radiation source.
- Switch objective lens to change magnification.
- Adjust current to magnetic lenses to change magnification.
- Highest practical magnification of 1,000 to 1,500 times.
- Highest practical magnification over 100,000 times.
- Uses electron beam for radiation source.
- Adjust current to magnetic lenses to change magnification.
What would be the best technique to prepare and view the internal structures of fungal hyphae?
TEM
A strain of Neisseria gonorrhoeae has undergone a mutation and is no longer able to make fimbriae. Predict the most likely outcome.
The bacteria will become less virulent and will not be able to readily establish infection.
Bacteria and archaea are typically fixed to slides by ____ while eukaryotes with subcellular structure, such as protists, are typically fixed by ___.
heat,chemicals
A __________ is a polysaccharide layer that lies outside the cell wall and is not easily removed.
capsule
What microscope would be the best to use to view cell surface features of a specimen?
SEM
component of the outer membrane in Gram-negative bacteria that results in septic shock upon entering the bloodstream?
lipopolysaccharide
The term used to describe bacteria that are intermediate in shape between spherical and rod-shaped is
coccobacilli.
Which bacterial structure may survive if temperatures applied during food preservation processes are too low?
endospores
Bacterial and archaeal ribosomes are known as _____ ribosomes, based on their sedimentation coefficient.
70S
Of the following choices, light passing through \_\_\_\_ would have the lowest refractive index. Oil Air Water Glass
air
The lipopolysaccharide (LPS) that is found in the outer membrane of gram-negative bacteria is also known as
endotoxin.
A fellow student carries out the Gram stain on a mixed culture containing Gram-negative rods and Gram-positive cocci and finds purple colored cocci and clear (no color) rods when viewing the prepared slide with a microscope. From the following, choose the best reason for these results:
The student did not add the primary stain.
The student decolorized the cells too much.
The student did not decolorize the cells long enough.
The student forgot to add the counterstain.
The student forgot to add the counterstain.
Which of the following contribute to the environmental resistance of bacterial endospores?
Lower pH
Spore coat
All of the choices are correct.
Presence of calcium dipicolinate
Low water content of endospore
All of the choices are correct.
An instrument that magnifies slight differences in the refractive index of cell structures is called a (n) __________ microscope.
phase-contrast
Flexible bacteria with a helical shape are called
spirochetes
Which of the following is not true of bacterial plasmids?
They can replicate independently of the chromosome.
They may carry genes for drug resistance.
They may carry genes that enhance survival of the bacterium under certain conditions.
They are required for host growth and/or reproduction.
They are required for host growth and/or reproduction.
After conducting the Gram stain on a mixed culture containing Gram-positive rods and Gram-negative cocci all the cells are purple in color. Most likely
the cells were not decolorized enough with alcohol or acetone.
After conducting the Gram stain on a mixed culture containing Gram-positive rods and Gram-negative cocci all the cells are purple in color. Most likely
the cells were not decolorized enough with alcohol or acetone.
Which of the following is/are true of capsules?
They help bacteria escape phagocytosis by host cells.
They retain water and help prevent desiccation of the bacteria.
They prevent entry of many bacterial viruses.
All of the above
All of the above
A/an ________ microscope keeps an object in focus when the objective lens is changed.
parfocal
A microscope that exposes specimens to ultraviolet, violet, or blue light and forms an image with the light emitted at a different wavelength is called a __________ microscope.
fluorescence
Order the objective lenses listed from the smallest to largest working distance that results when they are used.
oil immmersion; high power; low power
