What is the primary mode of replication in bacteriophages?
Answer: C
Bacteriophages replicate through either the lytic cycle (destroying the host cell) or lysogenic cycle (integrating DNA into host chromosome). Binary fission is bacterial reproduction.
Q.2Medium
Influenza virus belongs to which family?
Answer: B
Influenza viruses (types A, B, and C) belong to the family Orthomyxoviridae. They are enveloped, negative-sense RNA viruses with segmented genomes.
Q.3Medium
Which of the following is NOT a characteristic of viruses?
Answer: B
Viruses lack their own metabolic machinery and depend on host cell machinery for replication. Options A, C, and D are all characteristics of viruses.
Q.4Medium
What is the function of bacterial flagella in chemotaxis?
Answer: B
Flagella enable bacterial movement in response to chemical gradients (chemotaxis). Chemoreceptors detect signals, but flagella provide the locomotion. The other options are not functions of flagella.
Q.5Medium
Which antibiotic targets bacterial cell wall synthesis?
Answer: C
Penicillin inhibits peptidoglycan cross-linking in bacterial cell walls. Streptomycin targets ribosomes, tetracycline inhibits protein synthesis, and chloramphenicol inhibits 70S ribosomes.
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Q.6Medium
The envelope of enveloped viruses is derived from which structure?
Answer: B
Enveloped viruses acquire their envelope from host cell membranes (plasma membrane, nuclear envelope, or ER) during viral release. The envelope contains both host and viral proteins.
Q.7Medium
In bacterial conjugation, the F+ plasmid encodes which structure for DNA transfer?
Answer: B
The F (fertility) plasmid encodes the sex pilus (F pilus) that forms a bridge between F+ and F- cells for DNA transfer. This is bacterial conjugation, a horizontal gene transfer mechanism.
Q.8Medium
Which bacterial genus is primarily responsible for dental caries?
Answer: A
Streptococcus mutans is the primary causative agent of dental caries (cavities). It produces lactic acid from carbohydrate fermentation, demineralizing tooth enamel. Other listed bacteria cause different infections.
Q.9Medium
Which technique involves the use of restriction enzymes to cut bacterial DNA at specific sites?
Answer: C
RFLP uses restriction endonucleases to cut DNA at specific recognition sequences, creating fragments of variable lengths used for genetic analysis and bacterial strain identification.
Q.10Medium
A patient presents with severe respiratory infection. Gram-staining reveals gram-negative rods that are oxidase-positive and motile. Which organism is most likely responsible?
Answer: A
Pseudomonas aeruginosa is a gram-negative, oxidase-positive rod commonly causing respiratory infections in hospitalized patients. E. coli and Klebsiella are oxidase-negative, while Proteus is also oxidase-negative.
Q.11Medium
A laboratory identifies a virus with positive-sense, single-stranded RNA genome. Which process can this virus directly initiate without viral RNA-dependent RNA polymerase?
Answer: A
Positive-sense RNA can directly serve as mRNA for ribosomal translation. Replication requires RNA-dependent RNA polymerase. This genome type doesn't undergo reverse transcription or DNA synthesis.
Q.12Medium
A researcher observes that a bacterial strain previously sensitive to penicillin now survives treatment. Analysis shows increased production of beta-lactamase. This exemplifies which mechanism of antibiotic resistance?
Answer: B
Beta-lactamase enzymatically cleaves the beta-lactam ring of penicillin, inactivating the antibiotic. This is enzymatic degradation, not target modification or pump-mediated resistance.
Q.13Medium
In a clinical sample, Mycobacterium tuberculosis appears as acid-fast positive. This property is due to which cell wall component?
Answer: B
Mycolic acids in the mycobacterial cell wall resist acid-alcohol decolorization, causing the characteristic acid-fast staining. These long-chain fatty acids are unique to mycobacteria.
Q.14Medium
Which bacterial flagellar protein is the primary target of monoclonal antibodies used in serological identification?
Answer: A
Flagellin comprises the helical filament and constitutes the H (Hauch) antigen, used for serotyping bacteria like Salmonella. Other flagellar components are internal and less immunogenic.
Q.15Medium
In viral replication, which process involves the insertion of viral DNA into host chromosomes, as seen in retroviruses?
Answer: B
Integration is the process by which retroviral DNA (synthesized via reverse transcriptase) becomes incorporated into host genomic DNA. This establishes persistent infection and can cause insertional mutagenesis.
Q.16Medium
A patient with chronic Pseudomonas aeruginosa lung infection shows biofilm formation. Which virulence factor primarily enables this?
Answer: B
Pseudomonas aeruginosa produces alginate, a viscous polysaccharide exopolymer that forms the biofilm matrix, protecting bacteria from antibiotics and immune responses. This is characteristic of chronic respiratory infections.
Q.17Medium
In SARS-CoV-2, which structural protein is responsible for membrane fusion and is the primary target of neutralizing antibodies?
Answer: B
The spike protein mediates receptor binding and membrane fusion. It's the most exposed surface protein and elicits the strongest neutralizing antibody response, making it the vaccine target.
Q.18Medium
Which bacterial genus requires X factor (hemin) and V factor (NAD) for growth, making it fastidious?
Answer: B
Haemophilus species are fastidious gram-negative coccobacilli requiring both X factor (hemin) and V factor (NAD). Culture on chocolate agar provides these factors; they won't grow on regular blood agar.
Q.19Medium
A patient presents with community-acquired pneumonia. Culture on MacConkey agar shows non-fermentative, oxidase-positive colonies. Which organism is most likely?
Answer: B
Pseudomonas aeruginosa is a non-fermentative, oxidase-positive, Gram-negative rod commonly associated with respiratory infections and shows characteristic green pigmentation.
Q.20Medium
In viral pathogenesis, which mechanism allows RNA viruses like influenza to evade host immune response?
Answer: B
Antigenic drift (point mutations) and antigenic shift (reassortment of gene segments) allow influenza to escape previously acquired immunity, making vaccination necessary annually.
