BIOD 171 Microbiology Module 3 – Latest Updated 2025–2026 |
Microscopy, Staining & Laboratory Methods | 75 Questions and
Answers with Rationales
1. Which answer best identifies or explains the primary purpose of microscopy in microbiology?
A. to magnify and resolve structures too small to see unaided
B. to sterilize cultures
C. to measure antibiotic dose
D. to sequence DNA automatically
Answer: A. to magnify and resolve structures too small to see unaided
Rationale: Microscopy enables visualization of cells, structures, and arrangements that are below the
resolution of the unaided eye.
2. Which answer best identifies or explains magnification?
A. the amount of stain absorbed
B. the number of organisms alive
C. the apparent increase in image size
D. the ability to distinguish two close points
Answer: C. the apparent increase in image size
Rationale: Magnification enlarges the apparent size of an object.
3. Which answer best identifies or explains resolution?
A. the total magnification only
B. the ability to distinguish two nearby points as separate
C. the brightness of the lamp
D. the thickness of agar
Answer: B. the ability to distinguish two nearby points as separate
Rationale: Resolution determines image detail and is distinct from magnification.
4. Which answer best identifies or explains total magnification in a compound light microscope?
A. ocular plus objective magnification
B. ocular magnification multiplied by objective magnification
C. objective magnification divided by ocular
D. condenser power times stain concentration
Answer: B. ocular magnification multiplied by objective magnification
Rationale: Total magnification is the product of ocular and objective lens magnifications.
5. Which answer best identifies or explains the condenser on a light microscope?
A. a device that sterilizes slides
B. the lens used by the observer
C. the part that stores objectives
D. a lens system that focuses light on the specimen
Answer: D. a lens system that focuses light on the specimen
Rationale: The condenser concentrates illumination on the specimen.
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, 6. Which answer best identifies or explains the iris diaphragm?
A. a structure that regulates the amount of light reaching the specimen
B. the slide clip only
C. the coarse focus gear
D. the objective lens holder
Answer: A. a structure that regulates the amount of light reaching the specimen
Rationale: The iris diaphragm adjusts the light cone and affects contrast.
7. Which answer best identifies or explains oil immersion with the 100x objective?
A. a method that lowers magnification
B. a method that sterilizes the objective
C. a method that stains capsules
D. a technique that reduces light refraction and improves resolution
Answer: D. a technique that reduces light refraction and improves resolution
Rationale: Immersion oil has a refractive index similar to glass, allowing more light to enter the high-
power objective.
8. Which answer best identifies or explains bright-field microscopy?
A. a method that images surfaces with electrons
B. a method requiring fluorescent antibodies
C. a method in which stained or naturally pigmented specimens appear against a bright background
D. a method using an electron beam
Answer: C. a method in which stained or naturally pigmented specimens appear against a bright
background
Rationale: Bright-field microscopy is the standard light-microscopy approach for many stained microbial
specimens.
9. Which answer best identifies or explains phase-contrast microscopy?
A. a method useful for viewing living, unstained cells by converting phase differences to contrast
B. a surface electron-microscopy method
C. a method requiring heat fixation of every specimen
D. a staining method only
Answer: A. a method useful for viewing living, unstained cells by converting phase differences to
contrast
Rationale: Phase contrast enhances differences in refractive index without requiring staining.
10. Which answer best identifies or explains fluorescence microscopy?
A. microscopy using only transmitted white light
B. microscopy that detects light emitted by fluorophores after excitation
C. microscopy that requires no light source
D. microscopy using sound waves
Answer: B. microscopy that detects light emitted by fluorophores after excitation
Rationale: Fluorophores absorb shorter-wavelength light and emit longer-wavelength light that can be
detected.
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Microscopy, Staining & Laboratory Methods | 75 Questions and
Answers with Rationales
1. Which answer best identifies or explains the primary purpose of microscopy in microbiology?
A. to magnify and resolve structures too small to see unaided
B. to sterilize cultures
C. to measure antibiotic dose
D. to sequence DNA automatically
Answer: A. to magnify and resolve structures too small to see unaided
Rationale: Microscopy enables visualization of cells, structures, and arrangements that are below the
resolution of the unaided eye.
2. Which answer best identifies or explains magnification?
A. the amount of stain absorbed
B. the number of organisms alive
C. the apparent increase in image size
D. the ability to distinguish two close points
Answer: C. the apparent increase in image size
Rationale: Magnification enlarges the apparent size of an object.
3. Which answer best identifies or explains resolution?
A. the total magnification only
B. the ability to distinguish two nearby points as separate
C. the brightness of the lamp
D. the thickness of agar
Answer: B. the ability to distinguish two nearby points as separate
Rationale: Resolution determines image detail and is distinct from magnification.
4. Which answer best identifies or explains total magnification in a compound light microscope?
A. ocular plus objective magnification
B. ocular magnification multiplied by objective magnification
C. objective magnification divided by ocular
D. condenser power times stain concentration
Answer: B. ocular magnification multiplied by objective magnification
Rationale: Total magnification is the product of ocular and objective lens magnifications.
5. Which answer best identifies or explains the condenser on a light microscope?
A. a device that sterilizes slides
B. the lens used by the observer
C. the part that stores objectives
D. a lens system that focuses light on the specimen
Answer: D. a lens system that focuses light on the specimen
Rationale: The condenser concentrates illumination on the specimen.
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, 6. Which answer best identifies or explains the iris diaphragm?
A. a structure that regulates the amount of light reaching the specimen
B. the slide clip only
C. the coarse focus gear
D. the objective lens holder
Answer: A. a structure that regulates the amount of light reaching the specimen
Rationale: The iris diaphragm adjusts the light cone and affects contrast.
7. Which answer best identifies or explains oil immersion with the 100x objective?
A. a method that lowers magnification
B. a method that sterilizes the objective
C. a method that stains capsules
D. a technique that reduces light refraction and improves resolution
Answer: D. a technique that reduces light refraction and improves resolution
Rationale: Immersion oil has a refractive index similar to glass, allowing more light to enter the high-
power objective.
8. Which answer best identifies or explains bright-field microscopy?
A. a method that images surfaces with electrons
B. a method requiring fluorescent antibodies
C. a method in which stained or naturally pigmented specimens appear against a bright background
D. a method using an electron beam
Answer: C. a method in which stained or naturally pigmented specimens appear against a bright
background
Rationale: Bright-field microscopy is the standard light-microscopy approach for many stained microbial
specimens.
9. Which answer best identifies or explains phase-contrast microscopy?
A. a method useful for viewing living, unstained cells by converting phase differences to contrast
B. a surface electron-microscopy method
C. a method requiring heat fixation of every specimen
D. a staining method only
Answer: A. a method useful for viewing living, unstained cells by converting phase differences to
contrast
Rationale: Phase contrast enhances differences in refractive index without requiring staining.
10. Which answer best identifies or explains fluorescence microscopy?
A. microscopy using only transmitted white light
B. microscopy that detects light emitted by fluorophores after excitation
C. microscopy that requires no light source
D. microscopy using sound waves
Answer: B. microscopy that detects light emitted by fluorophores after excitation
Rationale: Fluorophores absorb shorter-wavelength light and emit longer-wavelength light that can be
detected.
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