BIOS 242 – FUNDAMENTALS OF
MICROBIOLOGY QUESTIONS
AND ANSWERS WITH
RATIONALES/GRADED A+/2026
UPDATE/100% CORRECT
/INSTANT DOWNLOAD
Midterm Examination (Latest 2026 Curriculum)
Part I: History & Microscopy (Questions 1-12)
1. Who was the first scientist to observe live microorganisms, which he called
"animalcules"?
• A) Robert Hooke
• B) Louis Pasteur
• C) Antonie van Leeuwenhoek
• D) Antonie van Leeuwenhoek
• Rationale: Van Leeuwenhoek ground simple microscopes and was the first to
observe and describe bacteria and protozoa (animalcules) in the 1670s.
2. Louis Pasteur’s Swan-neck flask experiment ultimately disproved which
theory?
• A) Germ theory of disease
• B) Biogenesis
• C) Spontaneous Generation
• D) Spontaneous Generation
, • Rationale: Pasteur demonstrated that broth remained sterile even when open
to air, as long as dust/microbes were trapped in the neck, disproving that life
arose spontaneously from non-living matter.
3. Which microscope is ideal for observing the internal structures of a living,
unstained cell?
• A) Scanning Electron Microscope (SEM)
• B) Transmission Electron Microscope (TEM)
• C) Phase-Contrast Microscope
• D) Phase-Contrast Microscope
• Rationale: Phase-contrast enhances contrast in transparent specimens
without killing or staining them, allowing observation of live cells.
4. If you are examining a virus that is 50 nm in diameter, which type of
microscope MUST you use?
• A) Light microscope
• B) Dark-field microscope
• C) Fluorescence microscope
• D) Electron microscope
• Rationale: The resolution of a light microscope is limited by the wavelength
of light (approx. 200 nm limit). Viruses are smaller than this and require an
electron beam.
5. In a brightfield microscope, what is the function of the condenser?
• A) Magnifies the image 10x
• B) Focuses light rays onto the specimen
• C) Focuses light rays onto the specimen
• D) Adjusts the resolution
• Rationale: The condenser concentrates and aligns light from the illuminator
onto the specimen to ensure even illumination.
6. Which lens is used for the initial focusing of a specimen under low power?
• A) Fine focus knob
• B) Coarse focus knob
• C) Iris diaphragm
• D) Condenser
• Rationale: The coarse focus knob moves the stage significantly to bring the
specimen into rough focus quickly.
7. Which staining technique differentiates bacteria based on the structure of
their cell walls (peptidoglycan thickness)?
, • A) Acid-fast stain
• B) Endospore stain
• C) Capsule stain
• D) Gram stain
• Rationale: The Gram stain uses crystal violet and safranin to distinguish
between Gram-positive (thick peptidoglycan, purple) and Gram-negative (thin
peptidoglycan, pink) bacteria.
8. You perform a Gram stain on a culture of E. coli. What color should the cells
appear under the microscope?
• A) Purple
• B) Blue
• C) Pink/Red
• D) Green
• Rationale: E. coli is a Gram-negative bacillus. It has a thin peptidoglycan layer
and an outer membrane; it cannot retain the crystal violet-iodine complex and
picks up the counterstain (safranin).
9. Why is the Acid-Fast stain clinically important?
• A) It identifies spores in Bacillus species.
• B) It identifies capsules in Streptococcus.
• C) It identifies Mycobacterium species.
• D) It identifies flagella arrangement.
• Rationale: Mycobacterium (e.g., tuberculosis) have waxy mycolic acid in their
walls that resists standard Gram stains, requiring acid-fast staining.
10. Which of the following is NOT a domain in the Woese-Fox system of
taxonomy?
• A) Bacteria
• B) Archaea
• C) Protista
• D) Eukarya
• Rationale: Carl Woese proposed the Three-Domain system based on rRNA
sequences. Protista is a kingdom within Eukarya, not a domain.
11. Which scientist developed a vaccination technique for Smallpox using
cowpox material?
• A) Robert Koch
• B) Paul Ehrlich
• C) Edward Jenner
• D) Joseph Lister
, • Rationale: Jenner observed that milkmaids who caught cowpox (vaccinia)
were immune to smallpox, leading to the first vaccine.
12. What is the magnification of the ocular (eyepiece) lens on most standard
laboratory microscopes?
• A) 4x
• B) 10x
• C) 40x
• D) 100x
• Rationale: Standard ocular lenses magnify the image 10 times. Total
magnification is ocular x objective.
Part II: Prokaryotic Cell Structure & Function (Questions 13-30)
13. Which of the following structures is present in ALL bacterial cells?
• A) Capsule
• B) Ribosomes
• C) Plasmid
• D) Flagellum
• Rationale: Ribosomes (70S) are required for protein synthesis and are
essential for survival. Capsules, plasmids, and flagella are accessory structures.
14. Bacteria that have a spherical shape are referred to as:
• A) Bacilli
• B) Cocci
• C) Vibrio
• D) Spirilla
• Rationale: "Coccus" (plural cocci) refers to round or spherical bacteria. Bacillus
is rod-shaped, Vibrio is curved.
15. Which structure is responsible for the "run and tumble" motility seen in E.
coli?
• A) Fimbriae
• B) Flagella
• C) Pili
• D) Slime layer
MICROBIOLOGY QUESTIONS
AND ANSWERS WITH
RATIONALES/GRADED A+/2026
UPDATE/100% CORRECT
/INSTANT DOWNLOAD
Midterm Examination (Latest 2026 Curriculum)
Part I: History & Microscopy (Questions 1-12)
1. Who was the first scientist to observe live microorganisms, which he called
"animalcules"?
• A) Robert Hooke
• B) Louis Pasteur
• C) Antonie van Leeuwenhoek
• D) Antonie van Leeuwenhoek
• Rationale: Van Leeuwenhoek ground simple microscopes and was the first to
observe and describe bacteria and protozoa (animalcules) in the 1670s.
2. Louis Pasteur’s Swan-neck flask experiment ultimately disproved which
theory?
• A) Germ theory of disease
• B) Biogenesis
• C) Spontaneous Generation
• D) Spontaneous Generation
, • Rationale: Pasteur demonstrated that broth remained sterile even when open
to air, as long as dust/microbes were trapped in the neck, disproving that life
arose spontaneously from non-living matter.
3. Which microscope is ideal for observing the internal structures of a living,
unstained cell?
• A) Scanning Electron Microscope (SEM)
• B) Transmission Electron Microscope (TEM)
• C) Phase-Contrast Microscope
• D) Phase-Contrast Microscope
• Rationale: Phase-contrast enhances contrast in transparent specimens
without killing or staining them, allowing observation of live cells.
4. If you are examining a virus that is 50 nm in diameter, which type of
microscope MUST you use?
• A) Light microscope
• B) Dark-field microscope
• C) Fluorescence microscope
• D) Electron microscope
• Rationale: The resolution of a light microscope is limited by the wavelength
of light (approx. 200 nm limit). Viruses are smaller than this and require an
electron beam.
5. In a brightfield microscope, what is the function of the condenser?
• A) Magnifies the image 10x
• B) Focuses light rays onto the specimen
• C) Focuses light rays onto the specimen
• D) Adjusts the resolution
• Rationale: The condenser concentrates and aligns light from the illuminator
onto the specimen to ensure even illumination.
6. Which lens is used for the initial focusing of a specimen under low power?
• A) Fine focus knob
• B) Coarse focus knob
• C) Iris diaphragm
• D) Condenser
• Rationale: The coarse focus knob moves the stage significantly to bring the
specimen into rough focus quickly.
7. Which staining technique differentiates bacteria based on the structure of
their cell walls (peptidoglycan thickness)?
, • A) Acid-fast stain
• B) Endospore stain
• C) Capsule stain
• D) Gram stain
• Rationale: The Gram stain uses crystal violet and safranin to distinguish
between Gram-positive (thick peptidoglycan, purple) and Gram-negative (thin
peptidoglycan, pink) bacteria.
8. You perform a Gram stain on a culture of E. coli. What color should the cells
appear under the microscope?
• A) Purple
• B) Blue
• C) Pink/Red
• D) Green
• Rationale: E. coli is a Gram-negative bacillus. It has a thin peptidoglycan layer
and an outer membrane; it cannot retain the crystal violet-iodine complex and
picks up the counterstain (safranin).
9. Why is the Acid-Fast stain clinically important?
• A) It identifies spores in Bacillus species.
• B) It identifies capsules in Streptococcus.
• C) It identifies Mycobacterium species.
• D) It identifies flagella arrangement.
• Rationale: Mycobacterium (e.g., tuberculosis) have waxy mycolic acid in their
walls that resists standard Gram stains, requiring acid-fast staining.
10. Which of the following is NOT a domain in the Woese-Fox system of
taxonomy?
• A) Bacteria
• B) Archaea
• C) Protista
• D) Eukarya
• Rationale: Carl Woese proposed the Three-Domain system based on rRNA
sequences. Protista is a kingdom within Eukarya, not a domain.
11. Which scientist developed a vaccination technique for Smallpox using
cowpox material?
• A) Robert Koch
• B) Paul Ehrlich
• C) Edward Jenner
• D) Joseph Lister
, • Rationale: Jenner observed that milkmaids who caught cowpox (vaccinia)
were immune to smallpox, leading to the first vaccine.
12. What is the magnification of the ocular (eyepiece) lens on most standard
laboratory microscopes?
• A) 4x
• B) 10x
• C) 40x
• D) 100x
• Rationale: Standard ocular lenses magnify the image 10 times. Total
magnification is ocular x objective.
Part II: Prokaryotic Cell Structure & Function (Questions 13-30)
13. Which of the following structures is present in ALL bacterial cells?
• A) Capsule
• B) Ribosomes
• C) Plasmid
• D) Flagellum
• Rationale: Ribosomes (70S) are required for protein synthesis and are
essential for survival. Capsules, plasmids, and flagella are accessory structures.
14. Bacteria that have a spherical shape are referred to as:
• A) Bacilli
• B) Cocci
• C) Vibrio
• D) Spirilla
• Rationale: "Coccus" (plural cocci) refers to round or spherical bacteria. Bacillus
is rod-shaped, Vibrio is curved.
15. Which structure is responsible for the "run and tumble" motility seen in E.
coli?
• A) Fimbriae
• B) Flagella
• C) Pili
• D) Slime layer
