,BIOD 171 Module 3 Exam | Essential Microbiology
| Portage Learning | Q & A | 2026 Edition
1. Which of the following best defines a nanometer?
A) 10⁻³ meters
B) 10⁻⁶ meters
C) 10⁻⁹ meters
D) 10⁻¹² meters
Correct Answer: 10⁻⁹ meters
Rationale: A nanometer is defined as 10⁻⁹ meters, or one-billionth of a meter. This is a standard unit of
measurement in microbiology for describing extremely small structures like viruses and cellular
components. A micrometer (10⁻⁶ m) is 1,000 times larger than a nanometer.
2. What is the primary function of the iris diaphragm on a compound light microscope?
A) To magnify the image of the specimen
B) To control the amount of light passing through the specimen
C) To focus the image by moving the stage up and down
D) To collect and concentrate light from the illuminator
Correct Answer: To control the amount of light passing through the specimen
Rationale: The iris diaphragm is an adjustable aperture that regulates the amount of light that reaches
the specimen. By opening or closing the diaphragm, the user can control light intensity and contrast,
which is critical for visualizing different types of samples.
3. Resolution and contrast are two critical factors that influence your ability to see an object. Which
statement accurately describes resolution?
A) The difference in light intensity between the specimen and the background
B) The ability to distinguish two adjacent objects as separate entities
,C) The total magnification power of the objective and ocular lenses
D) The capacity to make a specimen appear larger than its actual size
Correct Answer: The ability to distinguish two adjacent objects as separate entities
Rationale: Resolution is the microscope's ability to distinguish two points as separate entities; poor
resolution causes objects to appear merged. Contrast, in contrast, is the difference in light intensity
between the specimen and the background.
4. What is the total magnification of a sample when using a 60x objective and a 10x eyepiece?
A) 70x
B) 600x
C) 6000x
D) 60x
Correct Answer: 600x
Rationale: Total magnification is calculated by multiplying the magnification of the objective lens by that
of the ocular lens (eyepiece). Therefore, 60x multiplied by 10x equals 600x total magnification.
5. Which type of microscope is best suited for visualizing fluorescent proteins such as GFP, RFP, and YFP?
A) Bright-field microscope
B) Phase-contrast microscope
C) Dark-field microscope
D) Fluorescence microscope
Correct Answer: Fluorescence microscope
, Rationale: Fluorescence microscopy utilizes specific wavelengths of light to excite fluorophores (like GFP,
RFP, and YFP) which then emit light at a longer wavelength. This allows for the specific visualization of
proteins or structures tagged with these fluorescent markers.
6. Which type of microscope uses a specialized condenser to amplify slight differences between cells and
the background?
A) Fluorescence microscope
B) Phase-contrast microscope
C) Dark-field microscope
D) Confocal microscope
Correct Answer: Phase-contrast microscope
Rationale: Phase-contrast microscopy enhances contrast by amplifying the slight differences in refractive
index between cells and their surrounding medium. This allows living, unstained cells to be visualized
with greater detail than with bright-field microscopy.
7. Which type of microscope enhances contrast between the specimen and background but does not
permit the visualization of intracellular structures?
A) Phase-contrast microscope
B) Fluorescence microscope
C) Dark-field microscope
D) Bright-field microscope
Correct Answer: Dark-field microscope
Rationale: Dark-field microscopy creates a bright image of the specimen against a dark background by
blocking direct light and only collecting scattered light from the sample. While it enhances contrast for
external outlines, it does not reveal internal cellular details.
8. Which type of microscope is capable of capturing images in multiple focal planes to render a
specimen in 3D?
| Portage Learning | Q & A | 2026 Edition
1. Which of the following best defines a nanometer?
A) 10⁻³ meters
B) 10⁻⁶ meters
C) 10⁻⁹ meters
D) 10⁻¹² meters
Correct Answer: 10⁻⁹ meters
Rationale: A nanometer is defined as 10⁻⁹ meters, or one-billionth of a meter. This is a standard unit of
measurement in microbiology for describing extremely small structures like viruses and cellular
components. A micrometer (10⁻⁶ m) is 1,000 times larger than a nanometer.
2. What is the primary function of the iris diaphragm on a compound light microscope?
A) To magnify the image of the specimen
B) To control the amount of light passing through the specimen
C) To focus the image by moving the stage up and down
D) To collect and concentrate light from the illuminator
Correct Answer: To control the amount of light passing through the specimen
Rationale: The iris diaphragm is an adjustable aperture that regulates the amount of light that reaches
the specimen. By opening or closing the diaphragm, the user can control light intensity and contrast,
which is critical for visualizing different types of samples.
3. Resolution and contrast are two critical factors that influence your ability to see an object. Which
statement accurately describes resolution?
A) The difference in light intensity between the specimen and the background
B) The ability to distinguish two adjacent objects as separate entities
,C) The total magnification power of the objective and ocular lenses
D) The capacity to make a specimen appear larger than its actual size
Correct Answer: The ability to distinguish two adjacent objects as separate entities
Rationale: Resolution is the microscope's ability to distinguish two points as separate entities; poor
resolution causes objects to appear merged. Contrast, in contrast, is the difference in light intensity
between the specimen and the background.
4. What is the total magnification of a sample when using a 60x objective and a 10x eyepiece?
A) 70x
B) 600x
C) 6000x
D) 60x
Correct Answer: 600x
Rationale: Total magnification is calculated by multiplying the magnification of the objective lens by that
of the ocular lens (eyepiece). Therefore, 60x multiplied by 10x equals 600x total magnification.
5. Which type of microscope is best suited for visualizing fluorescent proteins such as GFP, RFP, and YFP?
A) Bright-field microscope
B) Phase-contrast microscope
C) Dark-field microscope
D) Fluorescence microscope
Correct Answer: Fluorescence microscope
, Rationale: Fluorescence microscopy utilizes specific wavelengths of light to excite fluorophores (like GFP,
RFP, and YFP) which then emit light at a longer wavelength. This allows for the specific visualization of
proteins or structures tagged with these fluorescent markers.
6. Which type of microscope uses a specialized condenser to amplify slight differences between cells and
the background?
A) Fluorescence microscope
B) Phase-contrast microscope
C) Dark-field microscope
D) Confocal microscope
Correct Answer: Phase-contrast microscope
Rationale: Phase-contrast microscopy enhances contrast by amplifying the slight differences in refractive
index between cells and their surrounding medium. This allows living, unstained cells to be visualized
with greater detail than with bright-field microscopy.
7. Which type of microscope enhances contrast between the specimen and background but does not
permit the visualization of intracellular structures?
A) Phase-contrast microscope
B) Fluorescence microscope
C) Dark-field microscope
D) Bright-field microscope
Correct Answer: Dark-field microscope
Rationale: Dark-field microscopy creates a bright image of the specimen against a dark background by
blocking direct light and only collecting scattered light from the sample. While it enhances contrast for
external outlines, it does not reveal internal cellular details.
8. Which type of microscope is capable of capturing images in multiple focal planes to render a
specimen in 3D?
