Q.1 What is the primary function of the bacterial cell membrane?
To store genetic information
To transport nutrients and waste
To produce energy via photosynthesis
To produce proteins
Explanation - The bacterial cell membrane regulates the movement of substances in and out of the cell, maintaining homeostasis.
Correct answer is: To transport nutrients and waste
Q.2 Which of the following is a common symptom of influenza infection?
Chest pain
High fever and cough
Weight loss
Blurred vision
Explanation - Influenza typically presents with fever, cough, sore throat, and body aches.
Correct answer is: High fever and cough
Q.3 What does the term 'virulence' refer to in microbiology?
The size of a bacterium
Its ability to survive in the environment
Its capacity to cause disease
Its resistance to antibiotics
Explanation - Virulence describes how effectively a pathogen can infect and damage a host.
Correct answer is: Its capacity to cause disease
Q.4 Which structure allows bacteria to adhere to host tissues?
Flagella
Capsule
Pili
Lipid bilayer
Explanation - Pili (fimbriae) are hair-like appendages that help bacteria attach to host cells.
Correct answer is: Pili
Q.5 What is the purpose of an immunization?
To treat an existing infection
To prevent disease by stimulating immunity
To diagnose a disease
To cure cancer
Explanation - Vaccines expose the immune system to an antigen, priming it to fight future infections.
Correct answer is: To prevent disease by stimulating immunity
Q.6 Which type of immunity is gained after recovering from a viral infection?
Passive immunity
Active natural immunity
Passive active immunity
Artificial immunity
Explanation - Active natural immunity develops after the body’s own response to an infection.
Correct answer is: Active natural immunity
Q.7 What is the main component of a bacterial peptidoglycan cell wall?
Chitin
Lipid A
Muramic acid
Glucose
Explanation - Peptidoglycan is a polymer of N-acetylglucosamine and N-acetylmuramic acid with cross-linked peptides.
Correct answer is: Muramic acid
Q.8 Which of these is a common method used to kill bacteria in medical settings?
UV radiation
Thermal pasteurization
Desiccation
All of the above
Explanation - UV, heat, and drying are all effective disinfectants for bacteria.
Correct answer is: All of the above
Q.9 What role does the spleen play in the immune system?
It stores hormones
It filters blood and removes old red cells
It produces insulin
It creates bone marrow cells
Explanation - The spleen removes damaged red blood cells and helps mount immune responses against blood-borne pathogens.
Correct answer is: It filters blood and removes old red cells
Q.10 Which of the following is NOT a symptom of bacterial meningitis?
Fever
Stiff neck
Seizures
Jaundice
Explanation - Jaundice is more commonly associated with liver disease or hemolysis, not meningitis.
Correct answer is: Jaundice
Q.11 What is the primary mechanism by which antibiotics such as penicillin work?
Inhibit protein synthesis
Disrupt DNA replication
Interfere with cell wall synthesis
Block electron transport chain
Explanation - Penicillin inhibits transpeptidase, preventing cross‑linking of peptidoglycan strands.
Correct answer is: Interfere with cell wall synthesis
Q.12 Which component of the immune system is responsible for producing antibodies?
Neutrophils
Macrophages
B lymphocytes
T lymphocytes
Explanation - B cells differentiate into plasma cells that secrete specific antibodies.
Correct answer is: B lymphocytes
Q.13 Which of the following is a type of viral envelope protein?
Capsid
Hemagglutinin
Toxin
Lipopolysaccharide
Explanation - Hemagglutinin is an envelope glycoprotein on influenza viruses that facilitates cell entry.
Correct answer is: Hemagglutinin
Q.14 What does the term ‘quorum sensing’ describe in bacterial communities?
The measurement of bacterial density
The exchange of genetic material via conjugation
Signal‑mediated regulation of group behavior
The process of spore formation
Explanation - Quorum sensing allows bacteria to coordinate activities like biofilm formation based on population density.
Correct answer is: Signal‑mediated regulation of group behavior
Q.15 Which immunoglobulin is predominantly found in mucosal secretions?
IgG
IgM
IgA
IgE
Explanation - IgA is the main antibody class in secretions like saliva and tears.
Correct answer is: IgA
Q.16 What is the role of dendritic cells in adaptive immunity?
To destroy pathogens directly
To present antigen to T cells
To produce cytokines for fever
To secrete antibodies
Explanation - Dendritic cells capture antigens and migrate to lymph nodes to activate T lymphocytes.
Correct answer is: To present antigen to T cells
Q.17 Which type of bacterial spore is most resistant to heat and desiccation?
Endospore
Cytoplasmic spore
Lysosomal spore
Germinating spore
Explanation - Bacterial endospores have a thick cortex and coat that protect them against extreme conditions.
Correct answer is: Endospore
Q.18 Which of the following is a hallmark of the innate immune response?
Memory cells
Specific antibody binding
Pattern recognition receptors
T cell receptor diversity
Explanation - Innate immunity uses PRRs like Toll‑like receptors to detect common pathogen motifs.
Correct answer is: Pattern recognition receptors
Q.19 What is the primary function of the complement system?
To produce antibodies
To mark pathogens for phagocytosis
To directly lyse host cells
To activate T cells
Explanation - Complement proteins opsonize pathogens, making them easier targets for phagocytes.
Correct answer is: To mark pathogens for phagocytosis
Q.20 Which bacterial species is commonly associated with dental caries?
Streptococcus mutans
Escherichia coli
Staphylococcus aureus
Salmonella enterica
Explanation - S. mutans ferments sugars to acids that demineralize tooth enamel.
Correct answer is: Streptococcus mutans
Q.21 What is a major risk factor for developing tuberculosis?
High vitamin C intake
Frequent exercise
Immunosuppression (e.g., HIV)
Low sodium diet
Explanation - Weak immune defenses allow latent TB infection to reactivate.
Correct answer is: Immunosuppression (e.g., HIV)
Q.22 Which of the following best describes a viral replication cycle?
Entry, genome replication, assembly, release
Entry, budding, mutation, death
Attachment, replication, sporulation, exit
Secretion, diffusion, ingestion, excretion
Explanation - Viruses hijack host machinery to replicate their nucleic acid, assemble new virions, and exit the cell.
Correct answer is: Entry, genome replication, assembly, release
Q.23 Which of the following is an example of a bacterial toxin that disrupts host cell membranes?
Cholera toxin
Exotoxin A
Alpha‑hemolysin
Tetanus toxin
Explanation - Alpha‑hemolysin forms pores in host cell membranes, causing cell lysis.
Correct answer is: Alpha‑hemolysin
Q.24 Which cell type is primarily responsible for the delayed allergic reaction known as anaphylaxis?
B lymphocytes
Eosinophils
Basophils
Neutrophils
Explanation - Basophils release histamine and other mediators that trigger anaphylaxis.
Correct answer is: Basophils
Q.25 What is the main difference between Gram‑positive and Gram‑negative bacteria?
Presence of flagella
Thickness of cell wall peptidoglycan
Genome size
Metabolic pathways
Explanation - Gram‑positive bacteria have a thick peptidoglycan layer; Gram‑negative have a thin layer plus an outer membrane.
Correct answer is: Thickness of cell wall peptidoglycan
Q.26 Which cytokine is primarily produced by Th1 cells to activate macrophages?
IL-4
IL-10
IFN‑γ
TNF‑α
Explanation - Interferon‑gamma stimulates macrophages to phagocytose intracellular pathogens.
Correct answer is: IFN‑γ
Q.27 What is the function of the blood–brain barrier in relation to infections?
To allow all bacteria into the brain
To selectively permit certain pathogens
To restrict entry of most microorganisms
To produce antibodies in the CNS
Explanation - The blood–brain barrier protects the CNS by filtering blood and preventing many pathogens from crossing.
Correct answer is: To restrict entry of most microorganisms
Q.28 Which of the following is a characteristic of a viral latent infection?
Continuous viral replication
Immediate cell death
Dormant viral genome within host cell
High production of viral toxins
Explanation - Latent viruses remain hidden until reactivation, producing no new virions during dormancy.
Correct answer is: Dormant viral genome within host cell
Q.29 What is the primary advantage of using a broad‑spectrum antibiotic?
Targets only one bacterial species
Targets multiple bacterial species
Has no side effects
Is free of resistance
Explanation - Broad‑spectrum antibiotics kill a wide range of bacteria, useful when the pathogen is unknown.
Correct answer is: Targets multiple bacterial species
Q.30 Which of the following best explains the principle behind an ELISA test?
Detection of nucleic acid sequences
Detection of antigen–antibody binding using enzyme conjugate
Observation of bacterial colonies on agar
Measurement of pH change
Explanation - ELISA uses enzyme‑linked antibodies to produce a measurable color change upon antigen detection.
Correct answer is: Detection of antigen–antibody binding using enzyme conjugate
Q.31 What does the term 'antigenic drift' refer to?
Large genetic changes in a pathogen
Small mutations leading to altered surface proteins
Complete elimination of a virus
The process of vaccine development
Explanation - Antigenic drift involves gradual mutations that help viruses evade immune detection.
Correct answer is: Small mutations leading to altered surface proteins
Q.32 Which immune cell type releases histamine in allergic reactions?
B cells
T cells
Basophils
Neutrophils
Explanation - Basophils contain histamine granules that are released during allergy triggers.
Correct answer is: Basophils
Q.33 What is the main role of the Fc region of an antibody?
Binds antigens
Recruits immune cells via Fc receptors
Activates complement cascade
Replicates inside cells
Explanation - The Fc domain interacts with Fc receptors on phagocytes and NK cells for effector functions.
Correct answer is: Recruits immune cells via Fc receptors
Q.34 Which of the following is a feature of a bacterial endospore?
Contains a single DNA molecule
Is metabolically active
Has a thick peptidoglycan wall
Can germinate under favorable conditions
Explanation - Endospores remain dormant until conditions allow them to revert to vegetative cells.
Correct answer is: Can germinate under favorable conditions
Q.35 Which of the following statements is true about the BCG vaccine?
It protects against smallpox
It is a live attenuated strain of Mycobacterium bovis
It is an inactivated vaccine
It is used to treat cancer
Explanation - BCG is a live vaccine derived from a weakened Mycobacterium bovis strain used against tuberculosis.
Correct answer is: It is a live attenuated strain of Mycobacterium bovis
Q.36 Which bacterial structure is responsible for the characteristic ‘smooth’ colony appearance?
Capsule
Flagella
Pili
Spore coat
Explanation - The capsule gives colonies a glossy, smooth look on agar plates.
Correct answer is: Capsule
Q.37 What is the primary mechanism of action of antiviral drug oseltamivir?
Inhibits DNA synthesis
Blocks viral hemagglutinin binding
Inhibits neuraminidase to prevent virus release
Destroys viral envelope
Explanation - Oseltamivir is a neuraminidase inhibitor that stops new influenza virions from leaving infected cells.
Correct answer is: Inhibits neuraminidase to prevent virus release
Q.38 Which of the following best describes a 'superbug'?
A bacteria that can grow at very high temperatures
A bacterium that has developed resistance to multiple antibiotics
A virus that mutates rapidly
A yeast that forms spores
Explanation - Superbugs refer to pathogens resistant to standard treatment regimens.
Correct answer is: A bacterium that has developed resistance to multiple antibiotics
Q.39 Which type of immunity is conferred by passive transfer of antibodies?
Active natural immunity
Active acquired immunity
Passive acquired immunity
Adaptive immunity
Explanation - Passive immunity involves receiving ready‑made antibodies from another source.
Correct answer is: Passive acquired immunity
Q.40 What is the major function of the T cell receptor (TCR)?
Binding to bacterial flagella
Recognizing peptide–MHC complexes
Producing antibodies
Phagocytosing pathogens
Explanation - TCRs specifically bind peptides presented by MHC molecules on antigen‑presenting cells.
Correct answer is: Recognizing peptide–MHC complexes
Q.41 Which bacterial toxin is responsible for causing food poisoning through heat‑stable enterotoxin?
Staphylococcal enterotoxin B
E. coli Shiga toxin
Clostridium difficile toxin A
Botulinum toxin
Explanation - Staphylococcal enterotoxin B is heat‑stable and causes rapid-onset foodborne illness.
Correct answer is: Staphylococcal enterotoxin B
Q.42 Which of the following is an example of a zoonotic disease?
Chickenpox
Tuberculosis in humans
Lyme disease
Meningitis
Explanation - Lyme disease is transmitted from animals (ticks) to humans, making it zoonotic.
Correct answer is: Lyme disease
Q.43 Which type of antibody is involved in the immediate hypersensitivity reaction?
IgG
IgA
IgE
IgM
Explanation - IgE antibodies bind allergens and trigger mast cell degranulation in allergies.
Correct answer is: IgE
Q.44 What is the main target of the human immune system during a bacterial septicemia?
Bacterial capsule
Host DNA
Bacterial ribosomes
Host mitochondria
Explanation - Capsules help bacteria evade phagocytosis; immune response focuses on neutralizing them.
Correct answer is: Bacterial capsule
Q.45 Which of the following describes a characteristic of Gram‑negative bacterial outer membrane?
Lipid A component of lipopolysaccharide
Thick peptidoglycan layer
Single‑layer phospholipid bilayer
Presence of teichoic acids
Explanation - Lipid A is a component of the LPS in Gram‑negative outer membranes, contributing to endotoxic activity.
Correct answer is: Lipid A component of lipopolysaccharide
Q.46 Which of the following best describes a pathogen’s ‘host‑specific’ adaptation?
Ability to infect multiple species
Specialized mechanisms to infect a single species
Resistance to antibiotics
Production of spores
Explanation - Host specificity arises when a pathogen has evolved to exploit a particular host’s cellular environment.
Correct answer is: Specialized mechanisms to infect a single species
Q.47 Which bacterial enzyme is targeted by the antibiotic vancomycin?
Peptidoglycan cross‑linking transpeptidase
DNA gyrase
RNA polymerase
MurA (UDP-N-acetylmuramic acid enolpyruvyl transferase)
Explanation - Vancomycin binds to the D‑alanine–D‑alanine terminus of peptidoglycan precursors, interfering with cell wall synthesis.
Correct answer is: MurA (UDP-N-acetylmuramic acid enolpyruvyl transferase)
Q.48 What does the term ‘pathogenicity island’ refer to?
A region of the bacterial genome encoding virulence factors
An area of the host where pathogens accumulate
A type of host immune cell
A membrane lipid unique to pathogens
Explanation - Pathogenicity islands are horizontally acquired genetic elements that enhance bacterial virulence.
Correct answer is: A region of the bacterial genome encoding virulence factors
Q.49 Which of the following is a hallmark of the innate immune system’s response to viral infection?
Production of IgE antibodies
Activation of complement via classical pathway
Interferon‑alpha and interferon‑beta secretion
Clonal expansion of T cells
Explanation - Interferons are antiviral cytokines produced quickly by infected cells to limit viral spread.
Correct answer is: Interferon‑alpha and interferon‑beta secretion
Q.50 Which of the following is an example of a bacterial biofilm?
Colonies of yeast on skin
Pseudomonas aeruginosa on a urinary catheter
Streptococcus mutans in dental plaque
Both b and c
Explanation - Both Pseudomonas on catheters and S. mutans in plaque are classic biofilms.
Correct answer is: Both b and c
Q.51 Which of the following best describes the process of immunological memory?
Immediate response to a pathogen
Long‑term retention of antigenic information by immune cells
Destruction of memory B cells
Production of new pathogens
Explanation - Memory cells persist after an infection, enabling a faster response upon re‑exposure.
Correct answer is: Long‑term retention of antigenic information by immune cells
Q.52 Which of the following is a characteristic feature of a bacterial exotoxin?
It is embedded in the bacterial cell membrane
It is secreted into the surrounding environment
It is a structural component of the capsule
It is produced only during stationary phase
Explanation - Exotoxins are actively secreted proteins that act on host tissues.
Correct answer is: It is secreted into the surrounding environment
Q.53 What is the primary function of the complement component C3?
Activates the classical complement pathway
Opsonizes pathogens for phagocytosis
Inhibits inflammation
Clears immune complexes
Explanation - C3b acts as an opsonin, tagging pathogens for recognition by phagocytes.
Correct answer is: Opsonizes pathogens for phagocytosis
Q.54 Which of the following best describes the term 'antigenic shift'?
Minor changes in antigenic structure
Large, abrupt changes in viral surface proteins
Loss of antigenicity entirely
Gradual accumulation of mutations
Explanation - Antigenic shift involves reassortment of viral genome segments, leading to new strains.
Correct answer is: Large, abrupt changes in viral surface proteins
Q.55 Which of the following is the most effective way to prevent transmission of tuberculosis?
Vaccination with BCG only
Isolation and antibiotic treatment of infectious cases
Frequent hand washing
Avoiding outdoor activities
Explanation - Preventing spread requires both isolating patients and treating them to eliminate the pathogen.
Correct answer is: Isolation and antibiotic treatment of infectious cases
Q.56 Which of the following best explains why antibiotic stewardship is essential?
To reduce the cost of antibiotics
To prevent the development of antibiotic resistance
To eliminate all bacteria
To speed up antibiotic production
Explanation - Judicious use of antibiotics helps preserve their effectiveness and curb resistance.
Correct answer is: To prevent the development of antibiotic resistance
Q.57 What is the main purpose of a bacterial flagellum?
To adhere to host tissues
To produce toxins
To provide motility
To synthesize DNA
Explanation - Flagella are rotary motors that propel bacteria through liquids.
Correct answer is: To provide motility
Q.58 Which of the following is a major component of the bacterial outer membrane?
Lipid A
Teichoic acids
Peptidoglycan
Flagellin
Explanation - Lipid A is a key part of the lipopolysaccharide (LPS) in Gram‑negative outer membranes.
Correct answer is: Lipid A
Q.59 What type of immunity does a person receive from an inactivated virus vaccine?
Active natural immunity
Active acquired immunity
Passive immunity
None of the above
Explanation - Inactivated vaccines stimulate the body's own adaptive immune response without infection.
Correct answer is: Active acquired immunity
Q.60 Which of the following is the mechanism of action of the antibiotic ciprofloxacin?
Inhibits DNA gyrase
Inhibits peptidoglycan cross‑linking
Inhibits protein synthesis
Inhibits folate synthesis
Explanation - Ciprofloxacin targets bacterial DNA gyrase, preventing DNA replication.
Correct answer is: Inhibits DNA gyrase
Q.61 Which of the following best describes the function of a bacterial capsule?
Facilitates DNA replication
Protects against phagocytosis
Provides energy for motility
Inhibits host cell apoptosis
Explanation - Capsules shield bacteria from host immune cells, especially phagocytes.
Correct answer is: Protects against phagocytosis
Q.62 Which of the following is a key characteristic of a viral genome that is segmented?
The genome is circular
The genome is divided into multiple distinct RNA or DNA segments
The genome is linear
The genome has no coding regions
Explanation - Segmented genomes allow reassortment during coinfection, contributing to antigenic shift.
Correct answer is: The genome is divided into multiple distinct RNA or DNA segments
Q.63 Which of the following is a hallmark of a Gram‑positive bacterial cell wall?
Thin peptidoglycan layer
Thick peptidoglycan layer
Outer membrane containing LPS
Presence of an electron transport chain
Explanation - Gram‑positive bacteria have a thick peptidoglycan layer that retains crystal violet stain.
Correct answer is: Thick peptidoglycan layer
Q.64 Which of the following best explains the function of interferon‑gamma in infection?
Stimulates B cell antibody production
Activates macrophages to destroy intracellular pathogens
Inhibits T cell proliferation
Inhibits phagocytosis
Explanation - Interferon‑gamma is a key cytokine that activates macrophages and enhances antigen presentation.
Correct answer is: Activates macrophages to destroy intracellular pathogens
Q.65 Which of the following is a major characteristic of bacterial toxins that target host cell membranes?
They require host cell receptors to enter
They form pores that disrupt membrane integrity
They are only produced in the stationary phase
They are inactivated by heat
Explanation - Pore‑forming toxins create openings in host cell membranes, leading to cell lysis.
Correct answer is: They form pores that disrupt membrane integrity
Q.66 What is the principal role of a B lymphocyte in the immune response?
To produce antibodies
To present antigens to T cells
To kill infected cells directly
To synthesize interferon
Explanation - B lymphocytes differentiate into plasma cells that secrete antibodies against specific antigens.
Correct answer is: To produce antibodies
Q.67 Which of the following is a common method used to detect bacterial endotoxins in a laboratory?
Gram staining
Latex agglutination
Limulus amebocyte lysate (LAL) assay
PCR
Explanation - The LAL test detects endotoxin (LPS) by measuring clotting reaction in horseshoe crab blood.
Correct answer is: Limulus amebocyte lysate (LAL) assay
Q.68 What is the main purpose of the host’s adaptive immune system during a bacterial infection?
To provide nonspecific defense
To develop a memory response for future infections
To produce toxins
To form a physical barrier
Explanation - Adaptive immunity tailors a specific response and retains memory for rapid future attacks.
Correct answer is: To develop a memory response for future infections
Q.69 Which of the following is a function of the bacterial outer membrane’s lipopolysaccharide (LPS) layer?
Provide energy
Act as an enzyme
Serve as an endotoxin and barrier
Facilitate DNA replication
Explanation - LPS is a potent endotoxin and provides protection against host defenses.
Correct answer is: Serve as an endotoxin and barrier
Q.70 Which of the following best describes a bacterial toxin that requires enzymatic modification of host proteins to exert its effect?
Hemolysin
Exotoxin A (toxin A)
Lipase
Protease
Explanation - Exotoxin A ADP‑ribosylates elongation factor 2, inhibiting protein synthesis.
Correct answer is: Exotoxin A (toxin A)
Q.71 What is a characteristic of a viral replication strategy that uses a reverse transcriptase?
The virus replicates its RNA into DNA
The virus replicates its DNA into RNA
The virus does not need a host cell
The virus can only infect plants
Explanation - Reverse transcriptase converts RNA to DNA, allowing integration into host genome.
Correct answer is: The virus replicates its RNA into DNA
Q.72 Which of the following is a primary reason why antibiotics are ineffective against viral infections?
Viruses lack ribosomes
Viruses do not have a cell wall
Both a and b
Viruses are resistant to all drugs
Explanation - Most antibiotics target bacterial structures absent in viruses, making them ineffective.
Correct answer is: Both a and b
Q.73 Which of the following is a key advantage of mucosal immunity?
Rapid systemic response
Protection at body surfaces where pathogens first enter
Production of high‑affinity antibodies
Long‑term memory formation only
Explanation - Mucosal immunity (IgA) defends the epithelium of respiratory, gastrointestinal, and urogenital tracts.
Correct answer is: Protection at body surfaces where pathogens first enter
Q.74 Which of the following best describes the role of macrophages in the immune system?
Produce antibodies
Consume and digest pathogens and debris
Produce interferon gamma
Serve as antigen‑presenting cells only
Explanation - Macrophages act as scavengers and phagocytes, engulfing and destroying microbes.
Correct answer is: Consume and digest pathogens and debris
Q.75 Which bacterial species is known for causing 'staph scalded skin syndrome'?
Streptococcus pyogenes
Staphylococcus aureus
Salmonella enterica
Pseudomonas aeruginosa
Explanation - S. aureus secretes exfoliative toxins that cause skin blistering.
Correct answer is: Staphylococcus aureus
Q.76 What is the most common mechanism of viral resistance to antiviral drugs?
Mutation of viral target enzyme
Inactivation by host enzymes
Destruction of host cell
All of the above
Explanation - Resistance often arises from mutations that reduce drug binding to viral enzymes.
Correct answer is: Mutation of viral target enzyme
Q.77 Which of the following is a hallmark of bacterial exotoxins?
They are embedded in the bacterial cell wall
They are secreted proteins that disrupt host cell function
They are part of the bacterial ribosome
They are only produced in the stationary phase
Explanation - Exotoxins are actively secreted and can damage host tissues or cells.
Correct answer is: They are secreted proteins that disrupt host cell function
Q.78 Which of the following best describes a 'spore-forming' bacterium?
It produces a thick protective coat around its DNA
It replicates by binary fission only
It requires oxygen for growth
It is resistant to antibiotics only
Explanation - Spore-forming bacteria create dormant endospores that resist harsh conditions.
Correct answer is: It produces a thick protective coat around its DNA
Q.79 Which of the following best explains the importance of antigen presentation to T cells?
It allows B cells to produce antibodies
It initiates the innate immune response
It enables T cells to recognize and respond to specific antigens
It helps in antibody class switching
Explanation - Antigen presentation activates T cells, essential for adaptive immunity.
Correct answer is: It enables T cells to recognize and respond to specific antigens
Q.80 Which of the following is a characteristic of the Gram‑negative outer membrane that contributes to antibiotic resistance?
It has porin proteins that allow free antibiotic entry
It contains lipopolysaccharide that can be modified to block antibiotics
It lacks an outer membrane
It is identical to Gram‑positive cell walls
Explanation - Gram‑negative bacteria can modify LPS to reduce permeability to antibiotics.
Correct answer is: It contains lipopolysaccharide that can be modified to block antibiotics
Q.81 Which of the following is a typical method for diagnosing bacterial meningitis?
Serum antibody titers
Lumbar puncture and cerebrospinal fluid analysis
Blood glucose test
X‑ray of the chest
Explanation - CSF analysis reveals characteristic changes indicating meningitis.
Correct answer is: Lumbar puncture and cerebrospinal fluid analysis
Q.82 Which of the following is a typical symptom of a fungal infection?
High fever and cough
Skin rash and itching
Severe headache
Abdominal pain
Explanation - Fungal infections often present with dermatological manifestations.
Correct answer is: Skin rash and itching
Q.83 Which of the following best describes the function of a bacterial plasmid?
Encodes for ribosomal RNA
Provides antibiotic resistance genes
Is essential for bacterial survival
Contains the bacterial genome
Explanation - Plasmids often carry genes that confer resistance to antibiotics.
Correct answer is: Provides antibiotic resistance genes
Q.84 Which of the following is an example of a viral envelope protein that facilitates entry into host cells?
Hemagglutinin
Capsid protein
Toxin
Flagellin
Explanation - Hemagglutinin binds to sialic acid receptors on host cells, mediating viral entry.
Correct answer is: Hemagglutinin
Q.85 Which of the following best describes a bacterial pathogenic factor known as a 'toxin'?
A protein that damages host tissues
A carbohydrate in the cell wall
A DNA fragment
An RNA polymerase subunit
Explanation - Toxins are substances produced by pathogens that harm host cells or tissues.
Correct answer is: A protein that damages host tissues
Q.86 Which of the following is a major cause of nosocomial infections?
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
All of the above
Explanation - These organisms commonly cause hospital-acquired infections.
Correct answer is: All of the above
Q.87 Which of the following is a typical feature of a bacterial phage?
It infects eukaryotic cells
It has a nucleic acid genome and protein capsid
It is a type of bacteria
It is a virus that infects plants only
Explanation - Bacteriophages are viruses that infect bacteria.
Correct answer is: It has a nucleic acid genome and protein capsid
Q.88 Which of the following is a characteristic of bacterial endotoxin?
Heat-labile
Derived from lipopolysaccharide
Produced by all bacteria
Requires host cell receptors to enter
Explanation - Endotoxins are part of the LPS of Gram‑negative bacteria and are heat‑stable.
Correct answer is: Derived from lipopolysaccharide
Q.89 What is a common method used to measure the growth of bacterial cultures in the laboratory?
pH measurement
Optical density at 600 nm (OD600)
Blood pressure measurement
Temperature reading
Explanation - OD600 correlates with bacterial cell density in liquid culture.
Correct answer is: Optical density at 600 nm (OD600)
Q.90 Which of the following best explains the mechanism of action of the drug rifampicin?
Inhibits DNA gyrase
Inhibits RNA polymerase
Inhibits cell wall synthesis
Inhibits folic acid synthesis
Explanation - Rifampicin binds to the beta subunit of bacterial RNA polymerase, blocking transcription.
Correct answer is: Inhibits RNA polymerase
Q.91 Which of the following is a feature of bacterial sporulation?
Rapid cell division
Formation of a resistant endospore
Increased metabolic activity
Loss of cell wall
Explanation - During sporulation, bacteria form durable endospores to survive adverse conditions.
Correct answer is: Formation of a resistant endospore
Q.92 Which of the following best describes the function of the complement component C5?
Opsonizes bacteria
Forms the membrane attack complex
Activates clotting cascade
Inhibits phagocytosis
Explanation - C5 is cleaved to C5a (chemotactic) and C5b, the latter initiating MAC formation.
Correct answer is: Forms the membrane attack complex
Q.93 Which of the following is a major determinant of bacterial pathogenicity?
Growth rate
Presence of virulence genes
Color of colonies
Nutrient requirement
Explanation - Virulence genes encode factors that enhance infection potential.
Correct answer is: Presence of virulence genes
Q.94 Which of the following best explains the term 'antigenic drift' in influenza viruses?
Complete genome reassortment
Minor changes in surface proteins
Loss of all antigenic sites
Rapid replication without mutation
Explanation - Antigenic drift involves point mutations altering viral epitopes.
Correct answer is: Minor changes in surface proteins
Q.95 Which of the following is a major role of macrophages in the immune system?
Produce antibodies
Consume pathogens via phagocytosis
Activate T cells directly
Secrete insulin
Explanation - Macrophages engulf and digest pathogens, presenting antigens to T cells.
Correct answer is: Consume pathogens via phagocytosis
Q.96 Which of the following best describes a bacterial capsule?
A protective outer membrane
A surface layer of polysaccharides or proteins
A component of the cytoskeleton
A protein involved in DNA replication
Explanation - Capsules protect bacteria from phagocytosis and desiccation.
Correct answer is: A surface layer of polysaccharides or proteins
Q.97 Which of the following best describes the role of IgM antibodies?
Primary antibody in secondary responses
First antibody produced in primary response
IgG subclass
IgE in allergic reactions
Explanation - IgM is produced early during the initial immune response.
Correct answer is: First antibody produced in primary response
Q.98 Which of the following is a characteristic of a bacterial endospore’s resistance?
Resistance to UV light
Resistance to heat
Resistance to antibiotics
All of the above
Explanation - Endospores can resist UV, heat, and many antibiotics.
Correct answer is: All of the above
Q.99 Which of the following best describes the mechanism of action of the antibiotic vancomycin?
Inhibits peptidoglycan cross‑linking by binding D‑alanine–D‑alanine
Inhibits DNA gyrase
Inhibits protein synthesis
Inhibits folic acid synthesis
Explanation - Vancomycin binds to the D‑alanine–D‑alanine termini, preventing cell wall synthesis.
Correct answer is: Inhibits peptidoglycan cross‑linking by binding D‑alanine–D‑alanine
Q.100 Which of the following best explains the function of the complement system?
Produce antibodies
Directly kill pathogens via the membrane attack complex
Produce hormones
Store immune cells
Explanation - Complement can form a pore‑forming complex that lyses target cells.
Correct answer is: Directly kill pathogens via the membrane attack complex
Q.101 Which of the following best describes the function of the B cell receptor (BCR)?
Recognizes peptide antigens presented by MHC
Recognizes whole pathogens directly
Recognizes DNA fragments
Recognizes antigens directly as antibodies
Explanation - BCRs are membrane-bound antibodies that bind free antigens.
Correct answer is: Recognizes antigens directly as antibodies
Q.102 Which of the following best explains the difference between a vaccine and an immunotherapy?
Vaccines are always live; immunotherapy is always passive
Vaccines induce active immunity; immunotherapy often provides passive immunity
Vaccines treat diseases; immunotherapy prevents disease
There is no difference
Explanation - Vaccines stimulate the body’s own adaptive immunity; immunotherapy often involves transfer of antibodies.
Correct answer is: Vaccines induce active immunity; immunotherapy often provides passive immunity
Q.103 Which of the following is a function of the immune system’s T-helper cells?
Produce antibodies
Assist B cells and cytotoxic T cells
Phagocytose pathogens
Produce insulin
Explanation - Helper T cells release cytokines that activate other immune cells.
Correct answer is: Assist B cells and cytotoxic T cells
Q.104 Which of the following best describes the role of interferon‑alpha in viral infections?
Inhibits viral replication
Promotes antibody production
Attracts neutrophils to the site of infection
Enhances phagocytosis of bacteria
Explanation - Interferon‑alpha is an antiviral cytokine that reduces viral replication.
Correct answer is: Inhibits viral replication
Q.105 Which of the following is a hallmark of a bacterial spore?
It contains a single DNA molecule
It is metabolically active
It is highly resistant to heat and desiccation
It is formed only in the presence of oxygen
Explanation - Bacterial spores can survive extreme conditions due to their protective coat.
Correct answer is: It is highly resistant to heat and desiccation
Q.106 Which of the following is the best explanation of why antibiotics are not effective against viruses?
Viruses lack a cell wall
Viruses are intracellular parasites
Both a and b
Viruses have a different genetic material
Explanation - Antibiotics target bacterial structures and functions absent in viruses.
Correct answer is: Both a and b
Q.107 Which of the following is a typical component of a bacterial virulence plasmid?
Toxin genes
Antibiotic resistance genes
Both a and b
Neither
Explanation - Virulence plasmids can carry toxins and resistance determinants.
Correct answer is: Both a and b
Q.108 Which of the following best describes a bacterial flagellum?
A motility structure powered by ATP
A structure that produces toxins
A part of the ribosomal complex
A type of plasmid
Explanation - Flagella rotate using proton motive force to propel bacteria.
Correct answer is: A motility structure powered by ATP
Q.109 Which of the following is the major function of the complement component C3b?
Cytotoxicity via membrane attack complex
Opsonization of pathogens
Chemotaxis of neutrophils
Inhibition of antibody production
Explanation - C3b tags microbes for phagocytosis.
Correct answer is: Opsonization of pathogens
Q.110 Which of the following best explains the term 'immune memory'?
The ability of the immune system to respond more quickly upon re‑exposure to an antigen
The presence of innate immunity only
The memory cells that survive for weeks
The memory of antibiotics
Explanation - Memory cells maintain information about pathogens for faster future responses.
Correct answer is: The ability of the immune system to respond more quickly upon re‑exposure to an antigen
Q.111 Which of the following best describes the function of a bacterial capsule?
It facilitates adhesion to host cells
It is a structural component of the cell wall
It protects against phagocytosis
It produces ATP
Explanation - The capsule creates a physical barrier against host immune cells.
Correct answer is: It protects against phagocytosis
Q.112 Which of the following best explains why a bacterial endospore is difficult to kill?
It has a double‑membrane structure
It contains a highly resistant core with low water content
It is metabolically active
It can replicate quickly
Explanation - The endospore core is dehydrated and protected by a thick coat.
Correct answer is: It contains a highly resistant core with low water content
Q.113 Which of the following best describes the role of T cells in the immune system?
Produce antibodies
Destroy infected cells directly or help B cells
Phagocytose pathogens
Secrete hormones
Explanation - Helper and cytotoxic T cells play critical roles in cellular immunity.
Correct answer is: Destroy infected cells directly or help B cells
Q.114 Which of the following is a feature of viral replication that involves reverse transcription?
Retroviruses
Herpesviruses
Picornaviruses
Flaviviruses
Explanation - Retroviruses use reverse transcriptase to convert RNA into DNA.
Correct answer is: Retroviruses
Q.115 Which of the following is a hallmark of bacterial endotoxins?
They are heat-labile
They are components of lipopolysaccharide (LPS)
They are secreted proteins
They are only present in Gram-positive bacteria
Explanation - Endotoxins are part of the outer membrane of Gram-negative bacteria.
Correct answer is: They are components of lipopolysaccharide (LPS)
Q.116 Which of the following best describes the role of the B cell receptor (BCR)?
It binds antigens and initiates B cell activation
It presents antigens to T cells
It secretes antibodies
It acts as a cytokine
Explanation - BCRs recognize soluble antigens and trigger B cell responses.
Correct answer is: It binds antigens and initiates B cell activation
Q.117 Which of the following best explains the mechanism of action of the antibiotic vancomycin?
Inhibits cell wall cross‑linking by binding D‑alanine–D‑alanine
Inhibits RNA polymerase
Inhibits DNA gyrase
Inhibits folate synthesis
Explanation - Vancomycin binds the D‑alanine–D‑alanine termini, blocking peptidoglycan cross‑linking.
Correct answer is: Inhibits cell wall cross‑linking by binding D‑alanine–D‑alanine
Q.118 Which of the following best describes the function of the complement component C5?
Opsonizes bacteria
Inhibits inflammation
Activates the membrane attack complex
Prevents phagocytosis
Explanation - C5 cleavage leads to formation of the MAC that lyses target cells.
Correct answer is: Activates the membrane attack complex