Free Acellular Life MCQs with Answers

• A. Dmitri Ivanovsky
• B. Louis Pasteur
• C. Alexander Fleming
• D. Edward Jenner

Explanation: In 1892 Ivanovsky filtered sap from diseased tobacco plants and found the filtrate still infectious, proving the agent was smaller than…

• A. sterile nutrient agar plates
• B. living cells, such as chick embryos or cell cultures
• C. rich broth shaken with oxygen
• D. extracts of sterile soil

Explanation: Because viruses have no metabolism of their own, they multiply only inside living host cells, so laboratories use cell cultures, chick…

• A. viroids
• B. plasmids
• C. bacteriophages
• D. prions

Explanation: Bacteriophages attach to specific receptors on the bacterial surface and inject their nucleic acid, making them powerful tools of genetics…

• A. influenza virus
• B. poliovirus
• C. HIV
• D. tobacco mosaic virus

Explanation: Wendell Stanley crystallised tobacco mosaic virus in 1935 and the crystals remained infectious, blurring the line between living and non…

• A. a head containing nucleic acid attached to a protein tail with tail fibres
• B. an RNA core surrounded by a lipid envelope only
• C. a single infectious protein molecule
• D. DNA enclosed in a polysaccharide capsule

Explanation: The phage's icosahedral head packs the DNA, and the hollow tail with base plate and fibres anchors to the bacterium and injects the…

• A. integration of viral DNA into the host chromosome
• B. bursting of the bacterium and release of new phage particles
• C. the virus becoming permanently dormant
• D. the bacterium turning into a virus

Explanation: After multiplication and assembly, lysozyme made by the phage dissolves the bacterial wall and the progeny escape to infect fresh cells.

• A. Cholera
• B. Tuberculosis
• C. Poliomyelitis
• D. Typhoid

Explanation: Polio is caused by the poliovirus, which attacks motor neurones and can cause paralysis.

• A. immunity produced by the vaccine lasts only days
• B. influenza virus infects only elderly people
• C. antibiotics destroy the vaccine
• D. the surface antigens of the virus mutate frequently

Explanation: Influenza's RNA genome mutates rapidly and its haemagglutinin and neuraminidase surface proteins keep changing, so last year's antibodies…

• A. contaminated drinking water
• B. the bite of Aedes mosquitoes
• C. coughing and sneezing
• D. eating contaminated food

Explanation: Aedes aegypti and Aedes albopictus mosquitoes carry the dengue virus between people, which is why outbreaks follow the mosquito season and…

• A. lack their own metabolism and the structures that antibiotics target
• B. are too small for drugs to reach
• C. live only in the soil
• D. are destroyed by stomach acid

Explanation: Antibiotics attack bacterial machinery such as cell walls and 70S ribosomes, and viruses possess neither, borrowing the host's instead.

• A. mosquito bites
• B. contaminated milk
• C. airborne droplets
• D. the bite of an infected animal such as a dog

Explanation: The rabies virus travels in the saliva of infected mammals and enters through a bite, then moves along nerves to the brain, causing…

• A. Hepatitis B
• B. Hepatitis C
• C. Hepatitis A
• D. Hepatitis D

Explanation: Hepatitis A, like hepatitis E, spreads by the faecal oral route through polluted food and water and usually resolves on its own.

• A. consist only of short circular RNA with no protein coat
• B. contain DNA genomes
• C. are larger than any virus
• D. infect only animals

Explanation: Viroids are the smallest known infectious agents, naked circles of RNA that cause plant diseases such as potato spindle tuber.

• A. release, assembly, biosynthesis, penetration, attachment
• B. attachment, penetration, biosynthesis, assembly, release
• C. biosynthesis, attachment, release, penetration, assembly
• D. penetration, release, attachment, assembly, biosynthesis

Explanation: The phage first attaches by its tail fibres, injects its DNA, then commandeers the host to make viral parts, assembles complete particles…

• A. DNA ligase
• B. RNA polymerase
• C. reverse transcriptase
• D. restriction endonuclease

Explanation: Reverse transcriptase copies the viral RNA into DNA, which then integrates into the host chromosome.

• A. antibodies on the cell surface
• B. MHC class one molecules
• C. antigen receptors of B lymphocytes
• D. CD4 receptors on helper T lymphocytes

Explanation: The viral glycoprotein gp120 fits the CD4 receptor, which is why helper T cells and macrophages, the CD4 bearing cells, are the targets.

• A. window period
• B. latent phase of AIDS
• C. incubation of tuberculosis
• D. vaccination period

Explanation: During the window period, which may last weeks to a few months, antibody tests can miss the infection even though the person is already…

• A. Blood
• B. Saliva
• C. Semen
• D. Vaginal secretions

Explanation: Blood, semen and vaginal secretions carry enough virus to transmit infection, but saliva contains too little and is even mildly antiviral.

• A. free virus particles circulating in the plasma
• B. virus crystals stored in lymph nodes
• C. viral DNA integrated into the chromosome of the host cell
• D. the inactive form of the virus outside the body

Explanation: Once reverse transcriptase makes the DNA copy, integrase inserts it into the host genome, where it can stay silent for years or direct the…

• A. the virus is too large for the immune system
• B. HIV infects only animals
• C. antibodies can never form against HIV
• D. the virus mutates its envelope proteins very rapidly

Explanation: The envelope glycoproteins change faster than a vaccine can be designed, and the virus hides inside cells as a provirus.