BIOL 271 Microbiology w/ Lab | Module 3: Microscopy and Microbial
Staining Techniques
200 Questions — Review Set
Question 1
The total magnification of a compound microscope is calculated by multiplying the
objective lens magnification by the ocular lens magnification. True or False?
✓ True
□ False
Correct Answer: True
Feedback: Total magnification = objective lens magnification × ocular lens magnification (typically 10×).
Question 2
What is the function of the condenser in a compound microscope?
✓ Answer: The condenser focuses light onto the specimen to improve illumination
and resolution.
Feedback: The condenser concentrates and directs light from the illuminator through the specimen.
Question 3
What is the resolving power (resolution) of a microscope?
✓ Answer: The ability to distinguish two closely spaced objects as separate entities.
Feedback: Resolution is determined by wavelength and numerical aperture; shorter wavelengths yield better
resolution.
Question 4
Oil immersion objectives require immersion oil between the lens and the slide to prevent
light refraction. True or False?
✓ True
□ False
Correct Answer: True
Feedback: Immersion oil has the same refractive index as glass, preventing light scatter and improving
resolution.
Question 5
What is the purpose of simple staining in microbiology?
, ✓ Answer: To color the cells so they can be more easily observed and to determine
cell morphology, size, and arrangement.
Feedback: Simple staining uses a single dye (e.g., methylene blue, crystal violet) to stain all cells uniformly.
Question 6
Which type of microscope uses visible light and a series of lenses to magnify specimens?
✓ Answer: Compound light microscope.
Feedback: The compound light microscope is the most common type used in teaching laboratories.
Question 7
The coarse focus knob should be used with the high-power objective (40×) to avoid
damaging the slide. True or False?
□ True
✓ False
Correct Answer: False
Feedback: The coarse focus should only be used with the scanning (4×) and low-power (10×) objectives; use
fine focus for high-power and oil immersion objectives.
Question 8
What is the numerical aperture (NA) of a lens?
✓ Answer: A measure of the light-gathering ability and resolving power of an
objective lens.
Feedback: Higher NA values indicate better resolution; NA = n × sin(θ), where n is the refractive index.
Question 9
What is the purpose of heat fixation in preparing a bacterial smear?
✓ Answer: To adhere the bacterial cells to the slide and kill the cells without
distorting their morphology.
Feedback: Heat fixation also denatures proteins, making cells more receptive to staining.
Question 10
Differential stains use more than one dye to distinguish between different types of bacteria.
True or False?
✓ True
□ False
,Correct Answer: True
Feedback: Differential stains (e.g., Gram stain, acid-fast stain) use multiple dyes to differentiate bacterial
groups.
Question 11
What is the Gram stain procedure?
✓ Answer: A differential staining method that divides bacteria into Gram-positive
(purple) and Gram-negative (pink) based on cell wall structure.
Feedback: The Gram stain involves crystal violet, iodine, decolorizer (alcohol/acetone), and safranin
counterstain.
Question 12
What is the primary stain used in the Gram stain?
✓ Answer: Crystal violet.
Feedback: Crystal violet is the initial dye applied to all cells in the Gram stain procedure.
Question 13
Gram-positive bacteria appear __________ after Gram staining.
✓ Answer: Purple/violet.
Feedback: Gram-positive bacteria have thick peptidoglycan layers that retain the crystal violet-iodine
complex.
Question 14
Gram-negative bacteria appear __________ after Gram staining.
✓ Answer: Pink/red.
Feedback: Gram-negative bacteria have thin peptidoglycan and outer membranes that do not retain crystal
violet after decolorization.
Question 15
What is the decolorizing agent used in the Gram stain?
✓ Answer: Alcohol or acetone-alcohol solution.
Feedback: The decolorizer removes the crystal violet from Gram-negative cells but not from Gram-positive
cells.
Question 16
What is the counterstain in the Gram stain?
, ✓ Answer: Safranin.
Feedback: Safranin stains the decolorized Gram-negative cells pink/red.
Question 17
The mordant used in the Gram stain is iodine. True or False?
✓ True
□ False
Correct Answer: True
Feedback: Iodine forms an insoluble complex with crystal violet that is trapped in Gram-positive cell walls.
Question 18
What is the purpose of the mordant in staining?
✓ Answer: To intensify the stain by forming an insoluble complex with the primary
dye.
Feedback: Mordants help fix dyes to cells, improving stain retention.
Question 19
What is an acid-fast stain used to identify?
✓ Answer: Bacteria with waxy mycolic acid in their cell walls, such
as Mycobacterium species.
Feedback: Acid-fast bacteria resist decolorization by acid-alcohol due to their lipid-rich cell walls.
Question 20
The primary stain in the acid-fast stain is carbolfuchsin. True or False?
✓ True
□ False
Correct Answer: True
Feedback: Carbolfuchsin is a lipophilic dye that penetrates the waxy cell walls of acid-fast bacteria.
Question 21
What is the decolorizer in the acid-fast stain?
✓ Answer: Acid-alcohol (3% HCl in 95% ethanol).
Feedback: Acid-alcohol decolorizes non-acid-fast bacteria while acid-fast bacteria retain the primary stain.
Question 22
Staining Techniques
200 Questions — Review Set
Question 1
The total magnification of a compound microscope is calculated by multiplying the
objective lens magnification by the ocular lens magnification. True or False?
✓ True
□ False
Correct Answer: True
Feedback: Total magnification = objective lens magnification × ocular lens magnification (typically 10×).
Question 2
What is the function of the condenser in a compound microscope?
✓ Answer: The condenser focuses light onto the specimen to improve illumination
and resolution.
Feedback: The condenser concentrates and directs light from the illuminator through the specimen.
Question 3
What is the resolving power (resolution) of a microscope?
✓ Answer: The ability to distinguish two closely spaced objects as separate entities.
Feedback: Resolution is determined by wavelength and numerical aperture; shorter wavelengths yield better
resolution.
Question 4
Oil immersion objectives require immersion oil between the lens and the slide to prevent
light refraction. True or False?
✓ True
□ False
Correct Answer: True
Feedback: Immersion oil has the same refractive index as glass, preventing light scatter and improving
resolution.
Question 5
What is the purpose of simple staining in microbiology?
, ✓ Answer: To color the cells so they can be more easily observed and to determine
cell morphology, size, and arrangement.
Feedback: Simple staining uses a single dye (e.g., methylene blue, crystal violet) to stain all cells uniformly.
Question 6
Which type of microscope uses visible light and a series of lenses to magnify specimens?
✓ Answer: Compound light microscope.
Feedback: The compound light microscope is the most common type used in teaching laboratories.
Question 7
The coarse focus knob should be used with the high-power objective (40×) to avoid
damaging the slide. True or False?
□ True
✓ False
Correct Answer: False
Feedback: The coarse focus should only be used with the scanning (4×) and low-power (10×) objectives; use
fine focus for high-power and oil immersion objectives.
Question 8
What is the numerical aperture (NA) of a lens?
✓ Answer: A measure of the light-gathering ability and resolving power of an
objective lens.
Feedback: Higher NA values indicate better resolution; NA = n × sin(θ), where n is the refractive index.
Question 9
What is the purpose of heat fixation in preparing a bacterial smear?
✓ Answer: To adhere the bacterial cells to the slide and kill the cells without
distorting their morphology.
Feedback: Heat fixation also denatures proteins, making cells more receptive to staining.
Question 10
Differential stains use more than one dye to distinguish between different types of bacteria.
True or False?
✓ True
□ False
,Correct Answer: True
Feedback: Differential stains (e.g., Gram stain, acid-fast stain) use multiple dyes to differentiate bacterial
groups.
Question 11
What is the Gram stain procedure?
✓ Answer: A differential staining method that divides bacteria into Gram-positive
(purple) and Gram-negative (pink) based on cell wall structure.
Feedback: The Gram stain involves crystal violet, iodine, decolorizer (alcohol/acetone), and safranin
counterstain.
Question 12
What is the primary stain used in the Gram stain?
✓ Answer: Crystal violet.
Feedback: Crystal violet is the initial dye applied to all cells in the Gram stain procedure.
Question 13
Gram-positive bacteria appear __________ after Gram staining.
✓ Answer: Purple/violet.
Feedback: Gram-positive bacteria have thick peptidoglycan layers that retain the crystal violet-iodine
complex.
Question 14
Gram-negative bacteria appear __________ after Gram staining.
✓ Answer: Pink/red.
Feedback: Gram-negative bacteria have thin peptidoglycan and outer membranes that do not retain crystal
violet after decolorization.
Question 15
What is the decolorizing agent used in the Gram stain?
✓ Answer: Alcohol or acetone-alcohol solution.
Feedback: The decolorizer removes the crystal violet from Gram-negative cells but not from Gram-positive
cells.
Question 16
What is the counterstain in the Gram stain?
, ✓ Answer: Safranin.
Feedback: Safranin stains the decolorized Gram-negative cells pink/red.
Question 17
The mordant used in the Gram stain is iodine. True or False?
✓ True
□ False
Correct Answer: True
Feedback: Iodine forms an insoluble complex with crystal violet that is trapped in Gram-positive cell walls.
Question 18
What is the purpose of the mordant in staining?
✓ Answer: To intensify the stain by forming an insoluble complex with the primary
dye.
Feedback: Mordants help fix dyes to cells, improving stain retention.
Question 19
What is an acid-fast stain used to identify?
✓ Answer: Bacteria with waxy mycolic acid in their cell walls, such
as Mycobacterium species.
Feedback: Acid-fast bacteria resist decolorization by acid-alcohol due to their lipid-rich cell walls.
Question 20
The primary stain in the acid-fast stain is carbolfuchsin. True or False?
✓ True
□ False
Correct Answer: True
Feedback: Carbolfuchsin is a lipophilic dye that penetrates the waxy cell walls of acid-fast bacteria.
Question 21
What is the decolorizer in the acid-fast stain?
✓ Answer: Acid-alcohol (3% HCl in 95% ethanol).
Feedback: Acid-alcohol decolorizes non-acid-fast bacteria while acid-fast bacteria retain the primary stain.
Question 22
