MCQ on Basics of Microbiology and Immunology

🦠 Basics of Microbiology (1–25)

1. Which of the following is a prokaryotic microorganism?
   A. Fungi
   B. Protozoa
   C. Bacteria✅
   D. Algae
   Explanation: Bacteria are prokaryotic, lacking a true nucleus.
2. The Gram staining technique differentiates bacteria based on:
   A. Cell wall composition✅
   B. Nucleus shape
   C. Capsule presence
   D. Motility
   Explanation: Gram-positive bacteria retain crystal violet due to thick peptidoglycan walls.
3. Which of the following structures helps bacteria move?
   A. Capsule
   B. Flagella✅
   C. Ribosome
   D. Pili
   Explanation: Flagella are tail-like structures responsible for bacterial motility.
4. Viruses differ from bacteria in that viruses:
   A. Have cell walls
   B. Require host cells to reproduce✅
   C. Contain both DNA and RNA
   D. Are unicellular
   Explanation: Viruses are obligate intracellular parasites.
5. Which of the following is used to sterilize heat-sensitive materials?
   A. Dry heat
   B. Filtration✅
   C. Boiling
   D. Autoclaving
   Explanation: Filtration removes microbes without using heat.
6. Bacterial endospores are resistant to:
   A. Freezing
   B. Heat and desiccation✅
   C. Antibiotics
   D. Nutrients
   Explanation: Endospores can survive harsh environmental conditions.
7. The phase where bacteria grow rapidly in culture is called:
   A. Lag phase
   B. Stationary phase
   C. Log (exponential) phase✅
   D. Death phase
   Explanation: The log phase is where cells divide at a constant rate.
8. Which enzyme is responsible for breaking down bacterial cell walls?
   A. DNA polymerase
   B. Lysozyme✅
   C. Catalase
   D. Reverse transcriptase
   Explanation: Lysozyme hydrolyzes peptidoglycan in cell walls.
9. Mycobacterium tuberculosis is best identified using:
   A. Gram stain
   B. India ink
   C. Acid-fast stain✅
   D. Capsule stain
   Explanation: Its waxy cell wall requires acid-fast staining.
10. Which type of microorganism is capable of photosynthesis?
    A. Cyanobacteria✅
    B. Fungi
    C. Protozoa
    D. Archaea
    Explanation: Cyanobacteria are photosynthetic prokaryotes.
11. An obligate anaerobe:
    A. Requires oxygen
    B. Prefers oxygen
    C. Cannot survive in the presence of oxygen✅
    D. Grows equally well with or without oxygen
    Explanation: Oxygen is toxic to obligate anaerobes.
12. Plasmids in bacteria often carry genes for:
    A. Antibiotic resistance✅
    B. Cell division
    C. Protein synthesis
    D. Endospore formation
    Explanation: Plasmids often contain non-essential but beneficial genes.
13. Which of the following is not a method of horizontal gene transfer?
    A. Conjugation
    B. Transformation
    C. Binary fission✅
    D. Transduction
    Explanation: Binary fission is vertical gene transfer.
14. Which of the following is used to culture viruses?
    A. Nutrient agar
    B. Blood agar
    C. Sabouraud agar
    D. Living host cells✅
    Explanation: Viruses require living cells to replicate.
15. Which microorganism causes malaria?
    A. Plasmodium✅
    B. Toxoplasma
    C. Giardia
    D. Entamoeba
    Explanation: Malaria is caused by Plasmodium species.
16. The main target of penicillin is:
    A. Cell membrane
    B. Cell wall synthesis✅
    C. DNA replication
    D. Protein synthesis
    Explanation: Penicillin inhibits peptidoglycan cross-linking.
17. Which of the following is a fungal infection?
    A. Tuberculosis
    B. Candidiasis✅
    C. Cholera
    D. Typhoid
    Explanation: Candida species cause fungal infections.
18. Bacteriophages are viruses that infect:
    A. Animals
    B. Bacteria✅
    C. Plants
    D. Fungi
    Explanation: “Bacteriophage” literally means bacteria-eater.
19. A biofilm is:
    A. A DNA strand
    B. A community of microorganisms✅
    C. A fungal toxin
    D. A viral capsid
    Explanation: Biofilms are structured communities of microbes.
20. The term “opportunistic pathogen” refers to an organism that:
    A. Causes disease in all hosts
    B. Causes disease in immunocompromised hosts✅
    C. Is always pathogenic
    D. Cannot cause disease
    Explanation: These microbes exploit weakened immune systems.
21. Which staining method is used to identify fungal elements?
    A. Gram stain
    B. KOH mount✅
    C. Acid-fast stain
    D. India ink
    Explanation: KOH dissolves host cells, leaving fungal structures visible.
22. Which bacteria are acid-fast?
    A. Streptococcus
    B. Mycobacterium✅
    C. E. coli
    D. Salmonella
    Explanation: Mycobacterium species resist decolorization by acid-alcohol.
23. Which virus has reverse transcriptase?
    A. Herpesvirus
    B. HIV✅
    C. Influenza
    D. Adenovirus
    Explanation: HIV is a retrovirus that uses reverse transcriptase.
24. What is a prion?
    A. A viral RNA
    B. A bacterial toxin
    C. An infectious protein✅
    D. A fungal spore
    Explanation: Prions are misfolded proteins that cause neurodegenerative diseases.
25. The most common method of bacterial reproduction is:
    A. Conjugation
    B. Binary fission✅
    C. Sporulation
    D. Budding
    Explanation: Bacteria divide asexually by binary fission.

🛡️ Basics of Immunology (26–50)

26. The primary lymphoid organs are:
    A. Lymph nodes and spleen
    B. Bone marrow and thymus✅
    C. Tonsils and Peyer’s patches
    D. Appendix and lymph nodes
    Explanation: These are where lymphocytes develop.
27. Which cell is responsible for antibody production?
    A. T-helper cell
    B. Plasma cell✅
    C. Macrophage
    D. NK cell
    Explanation: Plasma cells are activated B cells that secrete antibodies.
28. Which type of immunity is provided by vaccines?
    A. Natural active
    B. Passive natural
    C. Artificial active✅
    D. Artificial passive
    Explanation: Vaccines stimulate active immune responses.
29. Immunoglobulin G (IgG) is important for:
    A. Long-term immunity✅
    B. Mucosal defense
    C. Allergic reactions
    D. Primary response
    Explanation: IgG is the most abundant and provides lasting protection.
30. Which immune cells kill virus-infected cells?
    A. Cytotoxic T cells✅
    B. B cells
    C. Neutrophils
    D. Mast cells
    Explanation: Cytotoxic T cells recognize and destroy infected host cells.
31. The complement system enhances:
    A. Phagocytosis and cell lysis✅
    B. Antibody production
    C. Cell division
    D. T-cell activation
    Explanation: Complement proteins aid immune clearance of pathogens.
32. Which cell acts as an antigen-presenting cell?
    A. Erythrocyte
    B. Dendritic cell✅
    C. Platelet
    D. NK cell
    Explanation: Dendritic cells present antigens to T cells.
33. Which immunoglobulin is involved in allergic reactions?
    A. IgG
    B. IgM
    C. IgE✅
    D. IgA
    Explanation: IgE binds allergens and triggers histamine release.
34. Natural killer (NK) cells are part of:
    A. Adaptive immunity
    B. Innate immunity✅
    C. Passive immunity
    D. Autoimmunity
    Explanation: NK cells act rapidly without antigen specificity.
35. Which MHC class presents antigens to CD8+ T cells?
    A. Class I
    B. Class I✅
    C. Class II
    D. Class III
    Explanation: MHC I presents endogenous antigens to cytotoxic T cells.
36. Clonal selection refers to:
    A. Activation of specific lymphocytes✅
    B. Destruction of self-reactive T cells
    C. Phagocytosis of bacteria
    D. Release of histamines
    Explanation: Only lymphocytes with matching receptors are activated.
37. Autoimmune diseases occur when:
    A. Antibodies fail to form
    B. The immune system attacks self-tissues✅
    C. Immune cells are absent
    D. Foreign antigens enter the bloodstream
    Explanation: Immune tolerance fails, leading to tissue damage.
38. The first antibody produced in primary immune response is:
    A. IgG
    B. IgA
    C. IgM✅
    D. IgE
    Explanation: IgM is the first antibody released upon infection.
39. Which cytokine is crucial for inflammation?
    A. Interleukin-1 (IL-1)✅
    B. Interferon-alpha
    C. Interleukin-4
    D. IL-10
    Explanation: IL-1 is a key mediator of inflammatory responses.
40. Which type of hypersensitivity is anaphylaxis?
    A. Type II
    B. Type III
    C. Type I✅
    D. Type IV
    Explanation: IgE-mediated allergic response is classified as Type I.
41. T-helper cells (CD4+) assist in:
    A. Killing infected cells
    B. Activating B and T cells✅
    C. Phagocytosis
    D. Producing histamine
    Explanation: They help coordinate immune responses.
42. Passive immunity provides:
    A. Long-term protection
    B. Immediate, short-term protection✅
    C. Autoimmunity
    D. Vaccine failure
    Explanation: Antibodies are transferred directly (e.g., mother to baby).
43. Which structure traps pathogens in the respiratory tract?
    A. Lymph node
    B. Mucus✅
    C. Spleen
    D. Peyer’s patches
    Explanation: Mucus traps microbes for removal.
44. The spleen filters:
    A. Lymph
    B. Blood✅
    C. Urine
    D. Digestive enzymes
    Explanation: It removes old RBCs and pathogens from blood.
45. Which T cell subtype is involved in immune regulation?
    A. CD8+
    B. Cytotoxic T cell
    C. Regulatory T cell✅
    D. Memory B cell
    Explanation: Regulatory T cells prevent autoimmunity.
46. The function of memory cells is to:
    A. Provide faster secondary response✅
    B. Digest pathogens
    C. Prevent inflammation
    D. Neutralize toxins
    Explanation: They recognize and respond quickly to future infections.
47. Peyer’s patches are found in the:
    A. Stomach
    B. Small intestine✅
    C. Liver
    D. Pancreas
    Explanation: They monitor intestinal bacteria.
48. Interferons are produced in response to:
    A. Bacterial infection
    B. Viral infection✅
    C. Fungal exposure
    D. Allergens
    Explanation: Interferons help limit virus replication.
49. Antigens are:
    A. Antibody generators
    B. Proteins only
    C. Any substance that elicits an immune response✅
    D. Always harmful
    Explanation: Antigens trigger immune responses regardless of type.
50. Which organ is most involved in immune cell maturation?
    A. Liver
    B. Pancreas
    C. Thymus✅
    D. Appendix
    Explanation: The thymus is where T cells mature.