Q.1
Correct Option: A) Avoiding intravenous drugs
Explanation: HIV is primarily transmitted through direct contact with infected bodily fluids like blood, semen, and vaginal secretions. Intravenous drug use with shared needles is one of the most efficient transmission routes because it allows direct blood-to-blood contact. While other options like avoiding syringes (C) or direct contact (D) are important, intravenous drug avoidance is emphasized because needle-sharing is responsible for many HIV infections worldwide. Public health campaigns prioritize this prevention method.
Q.2
Correct Option: A) 2
Explanation: HIV is a retrovirus that carries its genetic material as two identical single-stranded RNA molecules. These RNA strands are packaged in the viral capsid and serve as templates for reverse transcription. The two RNA molecules may provide redundancy for successful infection. This is a defining characteristic of retroviruses in the Lentivirus genus.
Q.3
Correct Option: A) 2
Explanation: Each HIV virion contains two molecules of reverse transcriptase enzyme. This enzyme is crucial for converting viral RNA into DNA after the virus enters a host cell. Having two molecules ensures efficient reverse transcription and provides some error-checking capability during this process, though HIV’s reverse transcriptase is still error-prone, contributing to the virus’s high mutation rate.
Q.4
Correct Option: C) Reverse transcription
Explanation: HIV employs a unique process called reverse transcription, where its RNA genome is converted into DNA by the reverse transcriptase enzyme. This DNA then integrates into the host cell’s genome, allowing the virus to hijack the cell’s machinery for replication. This is why HIV is classified as a retrovirus (retro = backward, indicating the reverse flow of genetic information from RNA to DNA).
Q.5
Correct Option: B) Plasmid
Explanation: Plasmids are small, circular, double-stranded DNA molecules that exist independently of the bacterial chromosome. They replicate autonomously and often carry genes that confer advantages like antibiotic resistance or virulence factors. Plasmids are key tools in genetic engineering because they can be easily manipulated and transferred between bacteria. The nucleoid (A) refers to the bacterial chromosome, pili (C) are hair-like appendages for conjugation, and mesosomes (D) are invaginations of the plasma membrane.
Q.6
Correct Option: D) Transduction
Explanation: Transduction is a horizontal gene transfer mechanism where bacteriophages (viruses that infect bacteria) accidentally package bacterial DNA instead of viral DNA during their replication cycle. When these phages infect new bacteria, they transfer this DNA. This is distinct from transformation (direct DNA uptake from environment), conjugation (direct cell-to-cell DNA transfer via pili), or binary fission (asexual reproduction).
Q.7
Correct Option: C) Viruses use the host ribosomes for their own needs
Explanation: Viruses are obligate intracellular parasites that lack their own metabolic machinery, including ribosomes. They completely depend on the host cell’s ribosomes to translate viral mRNA into proteins. This is why viruses cannot reproduce outside a host cell. The other options are incorrect because viruses don’t carry ribosomes (A), don’t create new viral ribosomes (B), and do need ribosomes for protein synthesis (D).
Q.8
Correct Option: A) Motor neuron
Explanation: Poliovirus specifically targets motor neurons in the spinal cord, brainstem, and motor cortex. The destruction of these neurons leads to muscle weakness or paralysis, which is the hallmark of poliomyelitis. The virus enters through the oral route, replicates in the gut, and then invades the nervous system. This neurotropism makes polio particularly dangerous for the motor system.
Q.9
Correct Option: B) Virus
Explanation: Hepatitis D is caused by the hepatitis D virus (HDV), which is a defective RNA virus that requires the hepatitis B virus (HBV) to provide its envelope proteins for replication. HDV cannot cause infection without concurrent HBV infection. It’s not caused by bacteria (A), prions (C – infectious proteins), or viroids (D – infectious RNA molecules without protein coats).
Q.10
Correct Option: D) AIDS – DNA
Explanation: This is mismatched because AIDS is caused by HIV, which is an RNA virus (specifically a retrovirus). The other pairings are correct: smallpox is caused by a DNA virus (variola virus), influenza is an RNA virus, and measles is caused by an RNA virus (paramyxovirus). This question tests knowledge of viral classification based on nucleic acid type.
Q.11
Correct Option: B) Salk
Explanation: The Salk vaccine is an inactivated (killed) poliovirus vaccine administered via injection, while the Sabin vaccine (A) is a live attenuated oral vaccine. The Salk vaccine was the first effective polio vaccine developed and is safer for immunocompromised individuals.
Q.12
Correct Option: D) Hepatitis D virus
Explanation: Hepatitis D virus (HDV) is among the smallest known viruses, with a very simple structure consisting of a circular RNA genome surrounded by a protein capsid. It’s smaller than hepatitis A, C, or polioviruses. Its small size and dependence on HBV make it unique among human pathogens.
Q.13
Correct Option: B) Anthrax – Fowl cholera – Rabies
Explanation: Louis Pasteur developed vaccines for anthrax (1881), fowl cholera (1879), and rabies (1885). These were landmark achievements in microbiology. He did not develop vaccines for malaria (A) or chickenpox (C/D). His rabies vaccine was the first human vaccine created in a laboratory.
Q.14
Correct Option: C) Infective constituent in viruses is the protein coat.
Explanation: This statement is incorrect because the infective constituent of viruses is their nucleic acid (DNA or RNA), not the protein coat (capsid). The capsid protects the genetic material but doesn’t cause infection. The other options are correct: viroids lack protein coats (A), viruses are obligate parasites (B), and prions are misfolded proteins (D).
Q.15
Correct Option: C) Saccharomyces
Explanation: Saccharomyces (yeast) is a eukaryote, while Nostoc (A), Mycobacterium (B), and Oscillatoria (D) are prokaryotes (cyanobacteria and bacteria). This distinction is based on cellular organization – prokaryotes lack membrane-bound organelles and a true nucleus.
Q.16
Correct Option: C) 3
Explanation: HIV infection progresses through three clinical stages: acute infection (flu-like symptoms), clinical latency (asymptomatic but active replication), and AIDS (severe immune deficiency). The CDC classifies these stages based on CD4+ T-cell counts and clinical symptoms.
Q.17
Correct Option: B) RNA
Explanation: Retroviruses like HIV have single-stranded RNA as their genetic material, which is reverse-transcribed into DNA upon host cell entry. This DNA then integrates into the host genome. The term “retro” refers to this reverse flow of genetic information.
Q.18
Correct Option: C) DNA not bound to protein
Explanation: Bacterial genetic material consists of circular, double-stranded DNA that isn’t bound to histones (unlike eukaryotic DNA). It’s packaged in the nucleoid region but lacks the chromatin structure of eukaryotes. Bacterial DNA is “naked” compared to eukaryotic DNA.
Q.19
Correct Option: D) All the above
Explanation: Mycoplasmas, spirochetes, and rickettsiae are all prokaryotes that contain DNA (genetic material), RNA (for protein synthesis), and ribosomes (for translation). Despite their structural differences, they share these fundamental cellular components.
Q.20
Correct Option: D) Mycoplasma
Explanation: Mycoplasmas are the smallest known free-living organisms (150-250 nm) and uniquely lack a cell wall. Their only boundary is the plasma membrane. This makes them resistant to antibiotics that target cell wall synthesis (like penicillin). They can cause pneumonia and other infections.
Q.21
Correct Option: D) Either a or b
Explanation: Viruses can contain either DNA or RNA as their genetic material, but never both simultaneously. DNA viruses include smallpox and herpes, while RNA viruses include HIV and influenza. The nucleic acid can be single- or double-stranded.
Q.22
Correct Option: B) Proteins and nucleic acid
Explanation: All viruses minimally consist of nucleic acid (DNA or RNA) enclosed in a protein capsid. Not all viruses have envelopes (A), carbohydrates/lipids (D), or both DNA and RNA (C). This is the most fundamental viral structure.
Q.23
Correct Option: D) Cold
Explanation: Over 200 distinct viruses (mainly rhinoviruses) cause the common cold, making it the most diverse viral illness. In contrast, AIDS is caused by HIV, hepatitis by a few specific viruses (A-E), and smallpox by variola virus alone.
Q.24
Correct Option: A) Haploid
Explanation: HIV is haploid because it carries a single copy of its RNA genome (two identical RNA strands are present but represent one genome). This differs from diploid organisms with two sets of chromosomes.
Q.25
Correct Option: D) All
Explanation: HIV carries three key enzymes: reverse transcriptase (RNA→DNA), integrase (inserts viral DNA into host genome), and protease (cleaves viral polyproteins into functional units). These are targets for antiretroviral drugs.
Q.26
Correct Option: A) Proteins
Explanation: Viruses lack ribosomes and metabolic enzymes, making them dependent on host cells for protein synthesis. While they also can’t synthesize carbohydrates or lipids independently, protein production is their most critical deficit.
Q.27
Correct Option: C) RNA instead of DNA
Explanation: HIV is a retrovirus because it uses RNA as its genetic material (unlike cellular organisms that use DNA). The “retro” refers to its reverse transcription of RNA into DNA, contrary to the central dogma (DNA→RNA→protein).
Q.28
Correct Option: B) Reovirus
Explanation: Reoviruses (including rotaviruses) are unique among animal viruses for having double-stranded RNA genomes. Most RNA viruses are single-stranded. TMV (A) has ssRNA, ΦX174 (C) has ssDNA, and cauliflower mosaic virus (D) has dsDNA.
Q.29
Correct Option: D) All the above
Explanation: Prokaryotes (bacteria/archaea) lack membrane-bound organelles like nuclei (A), Golgi (B), and mitochondria (C). Their DNA is in the nucleoid region, and metabolic functions occur in the cytoplasm or plasma membrane.
Q.30
Correct Option: C) Vibrio
Explanation: Vibrio bacteria (e.g., V. cholerae) are comma-shaped. Bacilli (A) are rod-shaped, spirilla (B) are spiral-shaped, and cocci (D) are spherical. Shape is a key characteristic in bacterial classification.
Q.31
Correct Option: A) Spherical
Explanation: Staphylococcus bacteria are cocci (spherical) that form grape-like clusters. Their name derives from Greek “staphyle” (grape) + “kokkos” (berry). This distinguishes them from rod-shaped (B/C) or cubical (D) bacteria.
Q.32
Correct Option: B) ss RNA
Explanation: HIV has a single-stranded RNA genome that is reverse-transcribed into DNA. This ssRNA is positive-sense (can serve directly as mRNA) and diploid (two copies per virion).
Q.33
Correct Option: C) Mitochondria
Explanation: Bacteria lack mitochondria; their respiratory enzymes are embedded in the plasma membrane. They do have cell walls (A), mesosomes (B – invaginations of the membrane), and RNA (D – for protein synthesis).
Q.34
Correct Option: B) Prophage
Explanation: A prophage is bacteriophage DNA integrated into a bacterial chromosome during the lysogenic cycle. This dormant viral DNA replicates with the host until it enters the lytic cycle. It’s a key mechanism of horizontal gene transfer.
Q.35
Correct Option: B) Cocci
Explanation: Cocci (spherical bacteria) are generally the smallest (0.5-1.0 μm), while bacilli (rods) and spirilla are larger. Mycoplasmas are even smaller but lack cell walls.
Q.36
Correct Option: A) Cell membrane
Explanation: Bacterial respiratory enzymes are located in the cell membrane (or mesosomes in some gram-positive bacteria). They lack mitochondria, so the membrane serves as the site for ATP production via oxidative phosphorylation.
Q.37
Correct Option: C) Nostoc
Explanation: Nostoc is a cyanobacterium (prokaryote), while Rhizopus (A – fungus), Spirogyra (B – alga), and Saccharomyces (D – yeast) are eukaryotes. Prokaryotes lack membrane-bound organelles.
Q.38
Correct Option: C) A-head, B-sheath, C-collar, D-tail fibers
Explanation: Bacteriophages have an icosahedral head (contains DNA), sheath (contractile tube for DNA injection), collar (connects head and tail), and tail fibers (for host attachment). This structure is adapted for bacterial infection.
Q.39
Correct Option: B) Viroids
Explanation: Viroids are small, circular RNA molecules that infect plants and lack protein coats. They differ from viruses (A/C) which have protein capsids, and mycoplasma (D) which are bacteria.
Q.40
Correct Option: D) Nucleoid
Explanation: The nucleoid is the irregularly shaped region in prokaryotes where chromosomal DNA is localized. It’s not membrane-bound like a nucleus (A) and lacks nucleoli (B). Plasmids (C) are extrachromosomal DNA.
Q.41
Correct Option: D) Monotrichous
Explanation: Monotrichous bacteria have a single flagellum at one pole (e.g., Vibrio cholerae). Peritrichous (A) means flagella all over; amphitrichous (B) means flagella at both ends; lophotrichous (C) means tufts of flagella at one/both poles.
Q.42
Correct Option: D) Pneumococcus
Explanation: Teichoic acids are found in gram-positive bacterial cell walls (e.g., Streptococcus pneumoniae). They stabilize the wall and bind cations. Mycoplasma (B) lacks a cell wall, and Nostoc (C) is gram-negative.
Q.43
Correct Option: A) RNA enveloped
Explanation: Mumps and measles viruses are paramyxoviruses with single-stranded RNA genomes and lipid envelopes derived from host membranes. Their envelopes contain fusion proteins that facilitate cell entry.
Q.44
Correct Option: C) Bacteriophage
Explanation: The description matches a bacteriophage’s complex structure (head, tail, fibers). Animal/plant viruses are typically simpler (icosahedral/helical), and viroids lack any protein structure.
Q.45
Correct Option: A) Biosonous fluid
Explanation: “Virus” comes from Latin “virus” meaning venom or poisonous liquid, reflecting early observations of infectious fluids. This term was later applied to filterable infectious agents smaller than bacteria.
Q.46
Correct Option: D) None
Explanation: HIV is highly host-specific to humans and doesn’t naturally infect pigs (A) or monkeys (B). SIV (simian immunodeficiency virus) infects monkeys but is distinct from HIV.
Q.47
Correct Option: A) Reverse transcriptase
Explanation: Reverse transcriptase is the enzyme that converts ssRNA into DNA in retroviruses like HIV. This is a unique process not found in cellular organisms.
Q.48
Correct Option: A) Prion
Explanation: Prions are infectious proteins (e.g., in mad cow disease) that lack nucleic acid. Viroids (B) have RNA, viruses (C) have DNA/RNA, and mycoplasma (D) are bacteria with both DNA and RNA.
Q.49
Correct Option: C) DNA and protein in prokaryotes
Explanation: The nucleoid (sometimes called gonophore) contains bacterial chromosomal DNA associated with proteins (not histones). These proteins help compact the DNA but differ from eukaryotic chromatin.
Q.50
Correct Option: A) RNA with protein
Explanation: HIV is an RNA virus with two ssRNA molecules packaged in a protein capsid. It’s not a DNA virus (B/C/D), though it forms DNA during its replication cycle.
