MCB 2000 Microbiology & Infection Control
Theory Midterm | 80 Practice Questions &
Answers | LVC Study Guide | 2026/2027
1. Which of the following scientists is credited with the discovery of penicillin?
• A. Louis Pasteur
• B. Robert Koch
• C. Alexander Fleming
• D. Joseph Lister
Rationale: Alexander Fleming discovered penicillin in 1928 from the
mold Penicillium notatum. Louis Pasteur is known for pasteurization and
germ theory, Robert Koch for identifying causative agents of diseases, and
Joseph Lister for antiseptic surgery.
2. What is the primary function of a bacterial capsule?
• A. Motility
• B. Protection from phagocytosis and desiccation
• C. Protein synthesis
• D. DNA replication
Rationale: The capsule is a viscous outer layer that protects the
bacterium from being engulfed by host phagocytic cells and helps it survive
in dry environments. Motility is provided by flagella, and protein
synthesis/DNA replication occur in the cytoplasm.
3. The Gram stain differentiates bacteria based on the structure of their:
• A. Cell membrane
• B. Ribosomes
, • C. Cell wall
• D. Nucleoid
Rationale: The Gram stain distinguishes bacteria based on the thickness
and composition of their peptidoglycan cell wall. Gram-positive bacteria
have a thick layer that retains the crystal violet-iodine complex, while Gram-
negative bacteria have a thin layer that does not.
4. Which of the following is NOT a domain in the three-domain system of
classification?
• A. Bacteria
• B. Archaea
• C. Eukarya
• D. Protista
Rationale: The three-domain system, developed by Carl Woese,
classifies life into Bacteria, Archaea, and Eukarya. Protista is a kingdom
within the domain Eukarya.
5. A microorganism that grows best in a high-salt environment is called a:
• A. Halophile
• B. Thermophile
• C. Acidophile
• D. Barophile
Rationale: A halophile is an organism that thrives in high salt
concentrations. A thermophile thrives at high temperatures, an acidophile
at low pH, and a barophile at high pressure.
6. The process by which a bacterium divides into two identical daughter cells is
called:
• A. Mitosis
, • B. Meiosis
• C. Binary fission
• D. Budding
Rationale: Binary fission is the primary method of reproduction for
bacteria, where a single cell divides into two genetically identical daughter
cells. Mitosis and meiosis are types of eukaryotic cell division.
7. Which of the following is a key component of the bacterial cell wall?
• A. Chitin
• B. Cellulose
• C. Peptidoglycan
• D. Ergosterol
Rationale: Peptidoglycan (murein) is the polymer that provides
structural strength to the bacterial cell wall. Chitin is found in fungi and
insects, cellulose in plants, and ergosterol in fungal cell membranes.
8. What type of microscope would be best for observing the detailed internal
structures of a mitochondrion?
• A. Compound light microscope
• B. Scanning electron microscope (SEM)
• C. Transmission electron microscope (TEM)
• D. Fluorescence microscope
Rationale: The Transmission Electron Microscope (TEM) passes
electrons through a thin specimen, providing extremely high resolution and
magnification (up to 100,000,000x) to view internal ultrastructures. SEM is
used for surface details.
9. Which of the following is NOT a characteristic of all living organisms?
• A. Metabolism
, • B. Reproduction
• C. Photosynthesis
• D. Evolution
Rationale: While all living things have metabolism, reproduce, and
evolve, not all perform photosynthesis. Many organisms, like animals and
fungi, are heterotrophs.
10. The causative agent of tuberculosis is:
• A. Escherichia coli
• B. Mycobacterium tuberculosis
• C. Streptococcus pneumoniae
• D. Staphylococcus aureus
Rationale: Tuberculosis is a disease caused by the bacterium
Mycobacterium tuberculosis. The other bacteria listed cause different types
of infections.
11. A relationship between two organisms where one benefits and the other is
harmed is called:
• A. Mutualism
• B. Commensalism
• C. Parasitism
• D. Synergism
Rationale: Parasitism is a symbiotic relationship where the parasite
benefits at the expense of the host. Mutualism benefits both, and
commensalism benefits one without affecting the other.
12. Which of the following is a primary lymphoid organ?
• A. Spleen
• B. Lymph node
Theory Midterm | 80 Practice Questions &
Answers | LVC Study Guide | 2026/2027
1. Which of the following scientists is credited with the discovery of penicillin?
• A. Louis Pasteur
• B. Robert Koch
• C. Alexander Fleming
• D. Joseph Lister
Rationale: Alexander Fleming discovered penicillin in 1928 from the
mold Penicillium notatum. Louis Pasteur is known for pasteurization and
germ theory, Robert Koch for identifying causative agents of diseases, and
Joseph Lister for antiseptic surgery.
2. What is the primary function of a bacterial capsule?
• A. Motility
• B. Protection from phagocytosis and desiccation
• C. Protein synthesis
• D. DNA replication
Rationale: The capsule is a viscous outer layer that protects the
bacterium from being engulfed by host phagocytic cells and helps it survive
in dry environments. Motility is provided by flagella, and protein
synthesis/DNA replication occur in the cytoplasm.
3. The Gram stain differentiates bacteria based on the structure of their:
• A. Cell membrane
• B. Ribosomes
, • C. Cell wall
• D. Nucleoid
Rationale: The Gram stain distinguishes bacteria based on the thickness
and composition of their peptidoglycan cell wall. Gram-positive bacteria
have a thick layer that retains the crystal violet-iodine complex, while Gram-
negative bacteria have a thin layer that does not.
4. Which of the following is NOT a domain in the three-domain system of
classification?
• A. Bacteria
• B. Archaea
• C. Eukarya
• D. Protista
Rationale: The three-domain system, developed by Carl Woese,
classifies life into Bacteria, Archaea, and Eukarya. Protista is a kingdom
within the domain Eukarya.
5. A microorganism that grows best in a high-salt environment is called a:
• A. Halophile
• B. Thermophile
• C. Acidophile
• D. Barophile
Rationale: A halophile is an organism that thrives in high salt
concentrations. A thermophile thrives at high temperatures, an acidophile
at low pH, and a barophile at high pressure.
6. The process by which a bacterium divides into two identical daughter cells is
called:
• A. Mitosis
, • B. Meiosis
• C. Binary fission
• D. Budding
Rationale: Binary fission is the primary method of reproduction for
bacteria, where a single cell divides into two genetically identical daughter
cells. Mitosis and meiosis are types of eukaryotic cell division.
7. Which of the following is a key component of the bacterial cell wall?
• A. Chitin
• B. Cellulose
• C. Peptidoglycan
• D. Ergosterol
Rationale: Peptidoglycan (murein) is the polymer that provides
structural strength to the bacterial cell wall. Chitin is found in fungi and
insects, cellulose in plants, and ergosterol in fungal cell membranes.
8. What type of microscope would be best for observing the detailed internal
structures of a mitochondrion?
• A. Compound light microscope
• B. Scanning electron microscope (SEM)
• C. Transmission electron microscope (TEM)
• D. Fluorescence microscope
Rationale: The Transmission Electron Microscope (TEM) passes
electrons through a thin specimen, providing extremely high resolution and
magnification (up to 100,000,000x) to view internal ultrastructures. SEM is
used for surface details.
9. Which of the following is NOT a characteristic of all living organisms?
• A. Metabolism
, • B. Reproduction
• C. Photosynthesis
• D. Evolution
Rationale: While all living things have metabolism, reproduce, and
evolve, not all perform photosynthesis. Many organisms, like animals and
fungi, are heterotrophs.
10. The causative agent of tuberculosis is:
• A. Escherichia coli
• B. Mycobacterium tuberculosis
• C. Streptococcus pneumoniae
• D. Staphylococcus aureus
Rationale: Tuberculosis is a disease caused by the bacterium
Mycobacterium tuberculosis. The other bacteria listed cause different types
of infections.
11. A relationship between two organisms where one benefits and the other is
harmed is called:
• A. Mutualism
• B. Commensalism
• C. Parasitism
• D. Synergism
Rationale: Parasitism is a symbiotic relationship where the parasite
benefits at the expense of the host. Mutualism benefits both, and
commensalism benefits one without affecting the other.
12. Which of the following is a primary lymphoid organ?
• A. Spleen
• B. Lymph node
