Which of the following bacteria is gram-positive and forms spores?
Answer: A
Bacillus subtilis is a gram-positive, rod-shaped bacterium capable of forming endospores. E. coli is gram-negative, V. cholerae is gram-negative curved rod, and P. aeruginosa is gram-negative.
Q.2Easy
The cell wall of bacteria primarily contains which polysaccharide?
Answer: B
Peptidoglycan is the major structural component of bacterial cell walls, forming a rigid framework. It contains N-acetylglucosamine and N-acetylmuramic acid linked by peptide bridges.
Q.3Easy
Which virus is responsible for causing COVID-19?
Answer: B
SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) is the virus responsible for the COVID-19 pandemic that emerged in late 2019. SARS-CoV-1 caused the 2003 outbreak.
Q.4Easy
Which of the following bacteria causes tuberculosis in humans?
Answer: B
Mycobacterium tuberculosis is the causative agent of tuberculosis (TB). M. leprae causes leprosy, C. diphtheriae causes diphtheria, and S. aureus causes various infections.
Q.5Easy
Which bacterial structure is responsible for motility in most bacteria?
Answer: B
Flagella are whip-like appendages that enable bacterial motility. Pili are used for attachment and DNA transfer, capsule provides protection, and mesosomes are infoldings of cell membrane.
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Q.6Easy
Which virus is a retrovirus and causes AIDS?
Answer: B
HIV is a retrovirus that carries reverse transcriptase enzyme to convert RNA to DNA. It causes acquired immunodeficiency syndrome (AIDS). Hepatitis B is a hepadnavirus, HSV is a herpesvirus.
Q.7Easy
Which virus causes chickenpox and shingles?
Answer: A
Varicella-zoster virus (VZV) causes varicella (chickenpox) in primary infection. The virus remains dormant in nerve tissue and reactivates as herpes zoster (shingles) later in life.
Q.8Easy
Which statement correctly describes the difference between prokaryotic and eukaryotic cells?
Answer: B
Prokaryotes (bacteria and archaea) lack a membrane-bound nucleus and organelles, with circular DNA. Eukaryotes (animals, plants, fungi) have a true nucleus and membrane-bound organelles with linear chromosomes.
Q.9Easy
Which of the following bacterial structures is responsible for horizontal gene transfer through direct cell-to-cell contact?
Answer: A
Pili (sex pili) mediate bacterial conjugation, enabling direct DNA transfer between cells. Flagella aid motility, capsules provide protection, and teichoic acids are cell wall components.
Q.10Easy
Which bacterial genus produces endospores as a survival mechanism under nutrient-depleted conditions?
Answer: A
Bacillus and Clostridium are the primary gram-positive bacteria capable of forming endospores. These structures are highly resistant to heat, chemicals, and radiation.
Q.11Easy
Which virus possesses a segmented genome and is responsible for causing influenza pandemics?
Answer: A
Influenza A virus has 8 RNA segments, enabling antigenic reassortment. This segmentation allows rapid evolution and pandemic potential through genetic exchange with other influenza strains.
Q.12Easy
A gram-positive coccus forms grape-like clusters and produces alpha-toxin. Which pathogen is being described?
Answer: B
Staphylococcus aureus characteristically forms clusters (not chains), produces alpha-hemolysin (alpha-toxin), and is coagulase-positive, distinguishing it from streptococci.
Q.13Easy
Which viral protein is responsible for recognizing and binding to host cell receptors during viral attachment?
Answer: B
Surface glycoproteins (spike proteins in coronaviruses, gp120 in HIV) mediate host cell recognition and attachment. Matrix proteins provide structural support; enzymes have catalytic roles.
Q.14Easy
A bacterial colony on blood agar shows beta-hemolysis and is catalase-positive, coagulase-positive. Which species is confirmed?
Answer: C
Staphylococcus aureus is catalase-positive (distinguishes from streptococci) and coagulase-positive (specific identification). Beta-hemolysis results from alpha-toxin production.
Q.15Easy
Which of the following bacterial cell wall components is responsible for the Gram-positive purple coloration in Gram staining?
Answer: A
Gram-positive bacteria have a thick peptidoglycan layer (20-80 nm) with teichoic acids that retains the crystal violet-iodine complex, resulting in purple coloration.
Q.16Easy
Which bacterial flagellar arrangement allows movement in a single direction with maximum efficiency?
Answer: B
Monotrichous bacteria have a single flagellum at one pole, enabling direct, efficient movement. Peritrichous flagella around the cell body create tumbling motion.
Q.17Easy
Which bacterial spore-forming genus is most commonly associated with food poisoning and produces heat-resistant endospores?
Which viral component is essential for attachment to host cell receptors and is the primary target for neutralizing antibodies?
Answer: C
Attachment proteins (like hemagglutinin in influenza, spike protein in SARS-CoV-2) mediate receptor binding and are immunodominant targets for neutralizing antibodies.
Q.19Easy
Which mycobacterial lipid component provides acid-fastness and represents a major virulence factor?
Answer: B
Mycolic acids in mycobacterial cell walls create a waxy, hydrophobic barrier that retains acid-fast stains and inhibits antimicrobial penetration.
Q.20Easy
A laboratory identifies a Gram-positive coccus in clusters that produces alpha-hemolysis on blood agar and coagulates plasma. What is the most probable identification?
Answer: C
Staphylococcus aureus produces coagulase enzyme (plasma coagulation positive), forming clusters and showing variable hemolysis (often alpha or non-hemolytic), distinguishing it from coagulase-negative staphylococci.
