,BIOL 271 Module 3 Exam | Microbiology w/ Lab |
Portage Learning | Q & A | 2026/2027 Edition
(PDF)
**1. Which unit of measurement is equal to one billionth of a meter?**
A) Micrometer
B) Millimeter
C) Nanometer
D) Centimeter
Correct Answer: Nanometer
Rationale: A nanometer (nm) is defined as 10⁻⁹ meters, which is one-billionth of a meter. A micrometer
(µm) is 10⁻⁶ meters, a millimeter is 10⁻³ meters, and a centimeter is 10⁻² meters. The nanometer is the
standard unit for measuring viruses and subcellular structures.
**2. The unaided human eye cannot reliably distinguish objects smaller than approximately:**
A) 1 mm
B) 0.1 mm
C) 10 µm
D) 1 µm
Correct Answer: 0.1 mm
Rationale: The resolution limit of the unaided human eye is approximately 0.1 mm (100 µm). Objects
smaller than this threshold cannot be distinguished as separate entities without the aid of a microscope.
This limitation necessitates the use of microscopy for visualizing bacteria, which are typically 0.5–5.0 µm
in size.
**3. Resolution is best defined as the ability to:**
,A) Make an image larger
B) Distinguish two adjacent points as separate
C) Add color to a specimen
D) Focus light onto the specimen
Correct Answer: Distinguish two adjacent points as separate
Rationale: Resolution (also called resolving power) is the ability of a microscope to distinguish two
closely spaced objects as separate entities. Poor resolution causes two objects to appear as one.
Magnification is the ability to enlarge an image, while contrast is the difference in light absorbance
between objects.
**4. Contrast in microscopy refers to:**
A) The ability to enlarge an image
B) The distance between two objects at which they can be seen as separate
C) The difference in light absorbance between two objects
D) The total magnification of the microscope
Correct Answer: The difference in light absorbance between two objects
Rationale: Contrast is the difference in light absorbance between two objects, which affects the ability to
distinguish them. Poor contrast results in a high background that makes visualization difficult. For
example, trying to identify dark objects at night (low light = low contrast) versus in bright sunlight (high
contrast). Staining enhances contrast.
**5. What are the two critical factors that influence the ability to see an object under a microscope?**
A) Magnification and illumination
B) Resolution and contrast
C) Objective power and eyepiece power
D) Wavelength and frequency
, Correct Answer: Resolution and contrast
Rationale: Resolution and contrast are the two critical factors that influence the ability to see an object.
Resolution determines whether two objects can be distinguished as separate, while contrast determines
how well an object stands out from its background. Both must be optimized for clear visualization.
**6. Assuming a constant light source power, which part of the microscope would you adjust to limit the
amount of light entering the microscope?**
A) Objective lens
B) Condenser
C) Iris diaphragm
D) Eyepiece
Correct Answer: Iris diaphragm
Rationale: The iris diaphragm controls the amount of light that passes through the sample and into the
objective lens. It can be adjusted (opened or closed) to alter the amount of light. The condenser focuses
light onto the specimen, the objective magnifies the image, and the eyepiece further magnifies the
image for the viewer.
**7. What is the total magnification of a sample imaged with a 60x objective and a 10x eyepiece?**
A) 60x
B) 70x
C) 600x
D) 6000x
Correct Answer: 600x
Rationale: Total magnification is calculated by multiplying the objective magnification by the eyepiece
(ocular) magnification. In this case, 60 × 10 = 600x. This calculation is standard for compound
microscopes, where the ocular lens typically provides 10x magnification.
Portage Learning | Q & A | 2026/2027 Edition
(PDF)
**1. Which unit of measurement is equal to one billionth of a meter?**
A) Micrometer
B) Millimeter
C) Nanometer
D) Centimeter
Correct Answer: Nanometer
Rationale: A nanometer (nm) is defined as 10⁻⁹ meters, which is one-billionth of a meter. A micrometer
(µm) is 10⁻⁶ meters, a millimeter is 10⁻³ meters, and a centimeter is 10⁻² meters. The nanometer is the
standard unit for measuring viruses and subcellular structures.
**2. The unaided human eye cannot reliably distinguish objects smaller than approximately:**
A) 1 mm
B) 0.1 mm
C) 10 µm
D) 1 µm
Correct Answer: 0.1 mm
Rationale: The resolution limit of the unaided human eye is approximately 0.1 mm (100 µm). Objects
smaller than this threshold cannot be distinguished as separate entities without the aid of a microscope.
This limitation necessitates the use of microscopy for visualizing bacteria, which are typically 0.5–5.0 µm
in size.
**3. Resolution is best defined as the ability to:**
,A) Make an image larger
B) Distinguish two adjacent points as separate
C) Add color to a specimen
D) Focus light onto the specimen
Correct Answer: Distinguish two adjacent points as separate
Rationale: Resolution (also called resolving power) is the ability of a microscope to distinguish two
closely spaced objects as separate entities. Poor resolution causes two objects to appear as one.
Magnification is the ability to enlarge an image, while contrast is the difference in light absorbance
between objects.
**4. Contrast in microscopy refers to:**
A) The ability to enlarge an image
B) The distance between two objects at which they can be seen as separate
C) The difference in light absorbance between two objects
D) The total magnification of the microscope
Correct Answer: The difference in light absorbance between two objects
Rationale: Contrast is the difference in light absorbance between two objects, which affects the ability to
distinguish them. Poor contrast results in a high background that makes visualization difficult. For
example, trying to identify dark objects at night (low light = low contrast) versus in bright sunlight (high
contrast). Staining enhances contrast.
**5. What are the two critical factors that influence the ability to see an object under a microscope?**
A) Magnification and illumination
B) Resolution and contrast
C) Objective power and eyepiece power
D) Wavelength and frequency
, Correct Answer: Resolution and contrast
Rationale: Resolution and contrast are the two critical factors that influence the ability to see an object.
Resolution determines whether two objects can be distinguished as separate, while contrast determines
how well an object stands out from its background. Both must be optimized for clear visualization.
**6. Assuming a constant light source power, which part of the microscope would you adjust to limit the
amount of light entering the microscope?**
A) Objective lens
B) Condenser
C) Iris diaphragm
D) Eyepiece
Correct Answer: Iris diaphragm
Rationale: The iris diaphragm controls the amount of light that passes through the sample and into the
objective lens. It can be adjusted (opened or closed) to alter the amount of light. The condenser focuses
light onto the specimen, the objective magnifies the image, and the eyepiece further magnifies the
image for the viewer.
**7. What is the total magnification of a sample imaged with a 60x objective and a 10x eyepiece?**
A) 60x
B) 70x
C) 600x
D) 6000x
Correct Answer: 600x
Rationale: Total magnification is calculated by multiplying the objective magnification by the eyepiece
(ocular) magnification. In this case, 60 × 10 = 600x. This calculation is standard for compound
microscopes, where the ocular lens typically provides 10x magnification.
