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Chapter 3 Micro
Terms in this set (71)
Which of the following is NOT equal to 1 mm?
A) 0.001 m
B) 100 μm
C) 106 nm
D) 0.1 cm
E) 10-3 m
A virus measures 100 nm in length. What is its length in μm?
A) 0.001 μm
B) 10 μm
C) 1 μm
D) 0.01 μm
C) 0.1 μm
Why is a specimen smaller than 200 nm not visible with a light microscope?
A) The lenses only go to 100 X magnification power.
B) It is too easy to lose on the stage.
C) Anything smaller than 200 nm cannot interact with visible light.
D) Visible light is only good at wavelengths below 390 nm.
Anything smaller than 200 nm cannot interact with visible light
What happens to the light rays when they hit the specimen?
A) They are reflected, refracted, or absorbed by the specimen.
B) They are diverted to the ocular lens.
C) They are absorbed by the stage.
D) They are focused into a small area towards the objective lens.
They are reflected, refracted, or absorbed by the specimen
What is the role of the ocular lens?
A)To recreate the image in the viewer's eye
B) To do the bulk of the magnification
C) To adjust the wavelength of light
D) To focus the light to a high intensity in a small area
To recreate the image in the viewer's eye
What is meant by light rays being divergent?
A) It is coming together to a focused beam
B) It is heading upwards
C) It is spreading out
It is spreading out
In a typical brightfield microscope (seen in the animation), at which point does magnification begin?
A) The stage
B) The ocular lens
C) The lamp
D) The objective lens
E) The condenser lens
The objective lens
What is the role of lenses in microscopy?
A) Lenses increase the contrast to determine structural differences in stained specimens.
B) Lenses are only used to magnify specimens that are smaller than whole red blood cells.
C) Lenses focus either light or electrons to create a magnified image of a specimen
Lenses focus either light or electrons to create a magnified image of a specimen
What structure does light pass through after leaving the condenser in a compound light microscope?
A) objective lens
C) ocular lens
Which microscope achieves the highest magnification and greatest resolution?
A) darkfield microscope
B) electron microscope
C) compound light microscope
D) fluorescence microscope
E) phase-contrast microscope
Which of the following correctly traces the path of light through the compound microscope?
A) condenser; light source; specimen; objective lens; ocular lens
B) condenser; light source; specimen; ocular lens; objective lens
C) light source; condenser; objective lens; specimen; ocular lens
D) light source; condenser; specimen; objective lens; ocular lens
E) light source; specimen; condenser; objective lens; ocular lens
light source; condenser; specimen; objective lens; ocular lens
What is the total magnification of a specimen viewed with a 10x ocular lens and a 45x objective lens?
The resolution of a microscope can be improved by changing the
C) wavelength of light.
D) coarse adjustment.
E) fine adjustment.
wavelength of light
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
A) larger than it would if immersion oil was used.
B) the same as it would if the immersion oil was used.
C) to have no color.
D) smaller than it would if immersion oil was used.
E) somewhat fuzzy and have poor resolution.
Somewhat fuzzy and have poor resolution
The purpose of a mordant in the Gram stain is to
A) make the flagella visible.
B) make the bacterial cells larger.
C) prevent the crystal violet from leaving the cells.
D) make gram-negative cells visible.
remove the simple stain.
Prevent the crystal violet from leaving the cells
You are performing a Gram stain on gram-negative bacteria and you stop after the decolorizer step. What is the appearance of the bacteria at this point?
You are performing a Gram stain on gram-positive bacteria and you stop after the addition of the counterstain. What is the appearance of the bacteria at this point?
Which type of stain is most useful in helping clinicians to decide which antibiotic to prescribe for a bacterial infection?
A) negative stain
B) flagella stain
C) endospore stain
D) simple stain
E) Gram stain
Assume you stain Bacillus by applying malachite green with heat and then counterstaining with safranin. Through the microscope, the green structures are
A) cell walls.
E)The answer cannot be determined.
Which step in the Gram stain is the critical step in differentiating gram-positive cells from gram-negative cells?
A) crystal violet
Bacterial smears are fixed before staining to
A) affix the cells to the slide.
B) make their walls permeable.
C) make the cells visible.
D) accept stain
affix the cells to the slide
The counterstain used in the Gram stain is a basic dye.
A student creates a Gram stain on a bacterial sample that has a mix of gram-negative and gram-positive organisms. The student accidentally forgets the decolorizer step. What would the outcome of the Gram stain be?
A) All organisms would appear purple (gram-positive).
B) All organisms would appear pink (gram-negative).
C) The Gram stain would show pink (gram-negative bacteria) and purple (gram-positive bacteria).
D) All organisms would appear colorless.
All organisms would appear purple (gram-positive)
Consider the following situations, and determine when a simple stain could be used instead of a Gram stain.
A) A wound specimen is being examined.
B) An unknown species of bacteria is being characterized and identified.
C) A microbiologist is trying to determine whether a specimen contains bacteria or fungi.
D) A specimen is suspected to contain multiple species of bacteria.
A microbiologist is trying to determine whether a specimen contains bacteria or fungi
Which of the following staining procedures is matched with the principal use for that stain?
A) acid-fast stain for microbes with waxy cell walls
B) negative stain used to differentiate cell wall components
C) endospore stain to visualize flagella
D) flagella stain used to distinguish dormant structures formed during adverse environmental conditions
acid-fast stain for microbes with waxy cell walls
The greater resolution of the electron microscope compared to the compound microscope is due to the longer wavelengths of the electrons used to examine specimens.
Which microscope is used to observe viruses and the internal structure of thinly sectioned cells?
A) brightfield microscope
B) darkfield microscope
C) scanning electron microscope
D)transmission electron microscope
E) fluorescence microscope
transmission electron microscope
Which microscope is best used for observing the surfaces of intact cells and viruses?
A) fluorescence microscope
B) darkfield microscope
C) phase-contrast microscope
D) brightfield microscope
E) scanning electron microscope
scanning electron microscope
Which microscope takes advantage of differences in the refractive indexes of cell structures?
A) darkfield microscope
B) phase-contrast microscope
C) electron microscope
D) compound light microscope
E) fluorescence microscope
Simple staining is often necessary to improve contrast in which microscope?
A) compound light microscope
B) phase-contrast microscope
C) fluorescence microscope
D) darkfield microscope
E) electron microscope
compound light microscope
What is the total magnification for the scanning lens
10 x 4x= 40 (TM)
What is the total magnification for the low lens
10 x 10x= 100 (TM)
What is the total magnification for the high lens
10 x 40x= 400 (TM)
What is the total magnification for the oil lense
10 x 100x= 1000 (TM)
What is resolution
The ability of the lens to distinguish two points
1. increased by short wavelength of light
2. lens system
adjusts the amount of light
Focuses light on specimen
big nob, moves stage up
small nob, helps focus
Once subject is in focus with the lower objective lens, it will remain in focus for the higher objective lens
Amount of light bending, measured as N value
What is the function of the Iris Diaphragm
allows you to adjust the amount of light that hits the specimen
Why do we need to use oil with the oil immersion lens
It helps to keep the light from bending and allows for a clear and finely detailed image of the specimen
ability to distinguish between two points
Distance between slide and objective lens
Field of View
How much you can see
-as magnification increases field of view decreases
- working distance as magnification increases working distance decreases
How much depth
- Microscope has a limited depth of focus
- Only part of a think specimen is in focus at any time
- Higher in magnification the thinner the focal plane
- dont cluster
- dont do arrangements
How big is bacteria
How big are viruses
What does a gram stain do?
Classifies bacteria into gram-positive or gram-negative
-tend to be killed by penicillin and detergents
-easier to kill
- thicker cell wall
ex: staphylococcus, streptococcus
-More resistant to antibiotics
-harder to kill
-thinner cell wall
-extra outer membrane *makes them harder to kill*
ex: e. coli
What is an Acid- Fast
cells that retain a basic stain in the presence of an acid-alcohol
unique cell wall with mycolic acid- waxy lipid
*makes the wall very tough
*hard to kill
Steps of gram staining
1.Primary Stain- Crystal violet
2. Iodine mordant
- traps CV- iodine in the G+ cells
3. Rinse with alcohol to make gram
-washes the CV-lo out of the G-
-CV-lo stays trapped in G+ because of thick wall
4. Counterstain- Safranin- stain G- pink
What is the shape, arrangement and gram status of Escherichia coli?
E. coli is gram negative
its shape is bacillus
it has no arrangements
it appears in clumps
If you gram stained a human cell, what color would they be and why?
a human cell would stain pink, human cells do not have a cell wall and therefore the primary stain would wash out with the alcohol rinse
What did we use to fix bacteria to the slide? Why is fixing important?
we used an alcohol fixation. fixing is important because it adheres the bacteria to the slide so it does not wash away.
If you skipped the iodine in the gram stain, what color would gram positive bacteria be at the end of the stain?
A lab receives a culture for gram staining on Thursday afternoon and they don't get to it. Friday is a holiday and the lab is closed on the weekend, so they store the culture and don't end up staining it until Monday afternoon. Will the results be accurate? Why or why not?
the results will not be accurate. the culture has been allowed to sit for too long and even if stored properly the bacteria is very likely to have used its food supply and will begin to die, and affect the cell wall. a compromised cell wall will not retain the primary stain, and after alcohol rinse they will all be clear and stain red/pink with the safranin counter stain
What color will all bacteria in a gram stain turn out if the culture is left for over 48-72 hours?
all bacteria will stain pink/red
What color do gram positive organisms become at the end of a gram staining procedure? How does the cell wall structure determine this outcome?
gram + organisms are purple at the end of a gram stain. the cell wall structure determines this outcome because of the think peptidoglycan cell wall that holds in primary stain ( crystal violet) after alcohol rinse
Indicate the three steps of preparing a culture for a gram stain procedure...
1. aseptic placement of bacteria on slide
2. let dry
3. alcohol fixation
Why is gram staining useful? Include a situation where it might help in the real-world.
Gram staining allows for a differentiation between a micro-organism with or without an LPS layer. This can help target a microorganism with an antibiotic in the healthcare field. Gram staining takes only minutes but IDing takes days.
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