Free Acellular Life MCQs with Answers

31. Rabies is transmitted to humans mainly through

• 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 hydrophobia. Prompt vaccination after a bite prevents the disease once symptoms appear, when it is almost always fatal.

32. Which hepatitis virus is transmitted mainly through contaminated food and water?

• 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. Hepatitis B and C travel in blood and body fluids and can cause chronic liver disease, so the route matters for prevention.

33. Viroids differ from viruses in that viroids

• 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. Viruses at least carry a protein capsid, so viroids are simpler still.

34. The correct sequence of the steps of the lytic cycle is

• 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 and finally releases them by lysing the cell. Any sequence that starts later in the list reverses cause and effect.

35. The enzyme HIV carries inside its capsid to make a DNA copy of its RNA genome is

• 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. The direction is the reverse of normal transcription, which is exactly what the name means, and it is this enzyme that drugs like AZT target.

36. HIV attaches to its target cell by binding to the

• 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. Destroying helper T cells collapses both arms of specific immunity, producing AIDS.

37. The interval between HIV infection and the appearance of detectable antibodies in the blood is called the

• 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 infectious. This is why blood banks also use nucleic acid tests to shorten the risk.

38. Which of the following body fluids is NOT normally an effective vehicle for transmitting HIV?

• 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. This is why sharing meals or kissing does not spread HIV, an important fact for removing stigma.

39. The provirus stage of HIV refers to

• 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 production of new virus. Integration is what makes the infection permanent and hard to cure.

40. No effective vaccine against HIV has yet been produced mainly because

• 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. Antibodies do form in infection, but they keep chasing a moving target, which is the real obstacle.