BIOL 271 Module 3 | Microbiology w/Lab Exam Q&A |
Portage Learning
1. Which of the following best defines the total magnification of a compound
microscope?
A) The magnification of the objective lens only
B) The magnification of the ocular lens only
C) The objective lens magnification multiplied by the ocular lens magnification
D) The objective lens magnification divided by the ocular lens magnification
Correct Answer: The objective lens magnification multiplied by the ocular lens
magnification
Rationale: Total magnification is calculated by multiplying the objective lens
magnification by the ocular lens magnification, which is typically 10×. For example, a
40× objective with a 10× eyepiece yields a total magnification of 400×. The ocular
and objective lenses work together to produce the final magnified image.
2. What is the primary function of the condenser in a compound light microscope?
A) To magnify the image of the specimen
B) To focus light onto the specimen for improved illumination and resolution
C) To hold the objective lenses in place
D) To adjust the coarse focus of the specimen
Correct Answer: To focus light onto the specimen for improved illumination and
resolution
Rationale: The condenser concentrates and directs light from the illuminator through
the specimen. Proper condenser adjustment is critical for achieving optimal
resolution and contrast. It does not magnify the image, hold objectives, or adjust
focus.
,3. The resolving power (resolution) of a microscope is defined as:
A) The ability to make an object appear larger
B) The ability to distinguish two closely spaced objects as separate entities
C) The total magnification of the microscope
D) The clarity of the image based on color
Correct Answer: The ability to distinguish two closely spaced objects as separate
entities
Rationale: Resolution is the ability to distinguish two closely spaced objects as
separate entities. It is determined by the wavelength of light and the numerical
aperture of the lens; shorter wavelengths yield better resolution. Magnification is the
increase in apparent size, which is different from resolution.
4. Why is immersion oil used with the 100× objective lens?
A) To increase the magnification of the lens
B) To prevent light refraction and improve resolution
C) To clean the lens after use
D) To stain the specimen for better visualization
Correct Answer: To prevent light refraction and improve resolution
Rationale: Immersion oil has the same refractive index as glass, preventing light
scatter and improving resolution. It allows the objective to capture more light,
resulting in a clearer, higher-resolution image. It does not increase magnification,
clean the lens, or stain the specimen.
5. Which focus knob should be used when viewing a specimen with the 40× high-
power objective?
A) Coarse focus knob
B) Fine focus knob
C) Both coarse and fine focus knobs simultaneously
,D) Neither, as the objective is not used for focusing
Correct Answer: Fine focus knob
Rationale: The coarse focus knob should only be used with the scanning (4×) and
low-power (10×) objectives. Using it with high-power or oil immersion objectives can
damage the slide or the lens. The fine focus knob provides precise focusing at higher
magnifications.
6. A student is observing a sample with a 60× objective and a 10× eyepiece. What is
the total magnification?
A) 60×
B) 70×
C) 600×
D) 6000×
Correct Answer: 600×
Rationale: Total magnification is calculated by multiplying the objective magnification
by the eyepiece magnification: 60× × 10× = 600×. The eyepiece (ocular) typically has
a 10× magnification. This is a fundamental calculation in light microscopy.
7. What is the primary purpose of heat fixation in preparing a bacterial smear?
A) To stain the bacterial cells
B) To adhere the bacterial cells to the slide and kill them without distorting their
morphology
C) To increase the size of the bacterial cells
D) To remove all contaminants from the slide
Correct Answer: To adhere the bacterial cells to the slide and kill them without
distorting their morphology
, Rationale: Heat fixation adheres the bacterial cells to the slide and kills the cells
without distorting their morphology. It also denatures proteins, making cells more
receptive to staining. It does not stain, increase cell size, or remove contaminants.
8. What is the simplest staining technique used to observe the size, shape, and
arrangement of bacterial cells?
A) Gram staining
B) Acid-fast staining
C) Simple staining
D) Endospore staining
Correct Answer: Simple staining
Rationale: Simple staining uses a single dye (e.g., methylene blue, crystal violet,
safranin) to color all cells uniformly. It is the easiest method for observing basic cell
morphology. Differential stains like Gram, acid-fast, and endospore stains are more
complex and differentiate between cell types.
9. Differential stains are characterized by:
A) Using a single dye to stain all cells
B) Using more than one dye to distinguish between different types of bacteria
C) Requiring no heat fixation
D) Being used only for observing viruses
Correct Answer: Using more than one dye to distinguish between different types of
bacteria
Rationale: Differential stains use more than one dye to distinguish between different
types of bacteria based on their cell wall composition or other structural differences.
The Gram stain, acid-fast stain, and endospore stain are all examples of differential
stains.
Portage Learning
1. Which of the following best defines the total magnification of a compound
microscope?
A) The magnification of the objective lens only
B) The magnification of the ocular lens only
C) The objective lens magnification multiplied by the ocular lens magnification
D) The objective lens magnification divided by the ocular lens magnification
Correct Answer: The objective lens magnification multiplied by the ocular lens
magnification
Rationale: Total magnification is calculated by multiplying the objective lens
magnification by the ocular lens magnification, which is typically 10×. For example, a
40× objective with a 10× eyepiece yields a total magnification of 400×. The ocular
and objective lenses work together to produce the final magnified image.
2. What is the primary function of the condenser in a compound light microscope?
A) To magnify the image of the specimen
B) To focus light onto the specimen for improved illumination and resolution
C) To hold the objective lenses in place
D) To adjust the coarse focus of the specimen
Correct Answer: To focus light onto the specimen for improved illumination and
resolution
Rationale: The condenser concentrates and directs light from the illuminator through
the specimen. Proper condenser adjustment is critical for achieving optimal
resolution and contrast. It does not magnify the image, hold objectives, or adjust
focus.
,3. The resolving power (resolution) of a microscope is defined as:
A) The ability to make an object appear larger
B) The ability to distinguish two closely spaced objects as separate entities
C) The total magnification of the microscope
D) The clarity of the image based on color
Correct Answer: The ability to distinguish two closely spaced objects as separate
entities
Rationale: Resolution is the ability to distinguish two closely spaced objects as
separate entities. It is determined by the wavelength of light and the numerical
aperture of the lens; shorter wavelengths yield better resolution. Magnification is the
increase in apparent size, which is different from resolution.
4. Why is immersion oil used with the 100× objective lens?
A) To increase the magnification of the lens
B) To prevent light refraction and improve resolution
C) To clean the lens after use
D) To stain the specimen for better visualization
Correct Answer: To prevent light refraction and improve resolution
Rationale: Immersion oil has the same refractive index as glass, preventing light
scatter and improving resolution. It allows the objective to capture more light,
resulting in a clearer, higher-resolution image. It does not increase magnification,
clean the lens, or stain the specimen.
5. Which focus knob should be used when viewing a specimen with the 40× high-
power objective?
A) Coarse focus knob
B) Fine focus knob
C) Both coarse and fine focus knobs simultaneously
,D) Neither, as the objective is not used for focusing
Correct Answer: Fine focus knob
Rationale: The coarse focus knob should only be used with the scanning (4×) and
low-power (10×) objectives. Using it with high-power or oil immersion objectives can
damage the slide or the lens. The fine focus knob provides precise focusing at higher
magnifications.
6. A student is observing a sample with a 60× objective and a 10× eyepiece. What is
the total magnification?
A) 60×
B) 70×
C) 600×
D) 6000×
Correct Answer: 600×
Rationale: Total magnification is calculated by multiplying the objective magnification
by the eyepiece magnification: 60× × 10× = 600×. The eyepiece (ocular) typically has
a 10× magnification. This is a fundamental calculation in light microscopy.
7. What is the primary purpose of heat fixation in preparing a bacterial smear?
A) To stain the bacterial cells
B) To adhere the bacterial cells to the slide and kill them without distorting their
morphology
C) To increase the size of the bacterial cells
D) To remove all contaminants from the slide
Correct Answer: To adhere the bacterial cells to the slide and kill them without
distorting their morphology
, Rationale: Heat fixation adheres the bacterial cells to the slide and kills the cells
without distorting their morphology. It also denatures proteins, making cells more
receptive to staining. It does not stain, increase cell size, or remove contaminants.
8. What is the simplest staining technique used to observe the size, shape, and
arrangement of bacterial cells?
A) Gram staining
B) Acid-fast staining
C) Simple staining
D) Endospore staining
Correct Answer: Simple staining
Rationale: Simple staining uses a single dye (e.g., methylene blue, crystal violet,
safranin) to color all cells uniformly. It is the easiest method for observing basic cell
morphology. Differential stains like Gram, acid-fast, and endospore stains are more
complex and differentiate between cell types.
9. Differential stains are characterized by:
A) Using a single dye to stain all cells
B) Using more than one dye to distinguish between different types of bacteria
C) Requiring no heat fixation
D) Being used only for observing viruses
Correct Answer: Using more than one dye to distinguish between different types of
bacteria
Rationale: Differential stains use more than one dye to distinguish between different
types of bacteria based on their cell wall composition or other structural differences.
The Gram stain, acid-fast stain, and endospore stain are all examples of differential
stains.
