Which of the following is a DNA virus?
A
Influenza virus
B
Hepatitis C virus
C
Varicella-zoster virus
D
Measles virus
Correct Answer:
C. Varicella-zoster virus
Varicella-zoster virus (VZV) is a double-stranded DNA virus belonging to the Herpesviridae family, causing chickenpox and shingles.
Endospores in bacteria are primarily formed for:
A
Reproduction
B
Survival under extreme environmental stress
C
Nutrient storage
D
Enhanced motility
Correct Answer:
B. Survival under extreme environmental stress
Endospores are dormant structures that allow bacteria like Bacillus and Clostridium to survive extreme temperatures, desiccation, and chemical stress.
Which viral structure is essential for cell recognition and attachment?
A
Matrix proteins
B
Spike proteins (S-protein)
C
Envelope lipids
D
RNA-dependent RNA polymerase
Correct Answer:
B. Spike proteins (S-protein)
Spike proteins on viral surfaces recognize and bind to specific receptors on host cells, determining viral tropism and infectivity.
Gram-positive bacteria retain crystal violet dye due to:
A
Presence of thick peptidoglycan layer
B
Absence of lipopolysaccharide
C
High lipid content in cell wall
D
Both A and B
Correct Answer:
D. Both A and B
The thick peptidoglycan layer in gram-positive bacteria traps the crystal violet-iodine complex, and absence of LPS distinguishes them from gram-negative bacteria.
Which of the following bacterial structures is responsible for adherence to host cells?
A
Pili and fimbriae
B
Flagella
C
Capsule only
D
Cell wall peptidoglycan
Correct Answer:
A. Pili and fimbriae
Pili and fimbriae are hair-like appendages that facilitate bacterial adhesion to host cells and surfaces, essential for pathogenesis.
Which of the following viruses has been successfully eradicated from the wild through vaccination programs?
A
Smallpox virus
B
Measles virus
C
Polio virus
D
Mumps virus
Correct Answer:
A. Smallpox virus
Smallpox was declared eradicated in 1980 following intensive global vaccination campaigns, the only human virus to achieve this status.
In bacterial DNA replication, which enzyme unwinds the double helix?
A
DNA helicase
B
DNA ligase
C
DNA polymerase
D
Primase
Correct Answer:
A. DNA helicase
DNA helicase breaks hydrogen bonds between base pairs to unwind the DNA double helix during replication.
Which viral envelope protein is primarily responsible for binding to host cell receptors in influenza virus?
A
Hemagglutinin
B
Neuraminidase
C
Matrix protein
D
RNA polymerase
Correct Answer:
A. Hemagglutinin
Hemagglutinin (H protein) binds to sialic acid receptors on host cells, initiating viral entry in influenza.
Which bacterial species is most commonly associated with food poisoning from poultry products?
A
Salmonella typhimurium
B
Listeria monocytogenes
C
Clostridium botulinum
D
Bacillus cereus
Correct Answer:
A. Salmonella typhimurium
Salmonella typhimurium is a major cause of foodborne illness from poultry, causing acute gastroenteritis.
What is the primary mode of transmission for Hepatitis A virus in developing countries?
A
Fecal-oral route
B
Bloodborne transmission
C
Respiratory droplets
D
Sexual contact
Correct Answer:
A. Fecal-oral route
HAV is transmitted through fecal-oral route, particularly in areas with poor sanitation and hygiene practices.
