32 practice MCQs on viruses, bacteriophages, viroids and prions, their structure, replication cycles and the diseases they cause. Every question has the correct answer and an explanation.
Start free — 20 questionsAcellular Life is part of the MDCAT Biology syllabus. This page collects Acellular Life MCQs in the style of past MDCAT papers — below are 12 of them with answers and explanations, and the full set of 32 questions is in the HighYield MDCAT QBank.
This chapter covers: viruses, bacteriophages, viroids and prions, their structure, replication cycles and the diseases they cause.
Correct answer: A. Blood transfusion
Hepatitis B is chiefly transmitted through blood transfusion and other exposure to infected blood, not through clotting defects or soil.
Correct answer: A. Influenza
Influenza is caused by an enveloped RNA virus and characteristically spreads in seasonal epidemic (and occasional pandemic) waves.
Correct answer: A. Landing > Tall contraction > Penetration > DNA Injection
A bacteriophage infects a bacterium in sequence: landing on the cell surface, penetration of the tail, tail sheath contraction, then DNA injection.
Correct answer: C. Obligative Intracellular Parasites
Viruses can only reproduce within a living host cell, making them obligate intracellular parasites.
Correct answer: A. A virus that infects bacteria
A bacteriophage is a type of virus that specifically infects bacteria. It attaches to the surface of bacterial cells and injects its genetic material into the host, taking over the bacterial machinery to replicate itself.
Correct answer: C. 6
Bacteriophages typically have tail fibers attached to the end plate. These tail fibers help the phage attach to specific receptors on the surface of the bacterial host cell. There are six long tail fibers attached to the end plate of a bacteriophage.
Correct answer: A. Interferons
Interferons are proteins that play a key role in controlling viral infections. They boost the body’s immune defenses and help limit the spread of viruses within the body. The other options listed (antigen, histone, and serum) are not molecules specifically used to control viruses during infection but may have other roles in immune responses or cellular processes.
Correct answer: C. Virion
A virion is the fully assembled, infectious form of a virus when it’s outside a host cell. It includes the genetic material along with its protective protein coat, and sometimes an envelope, allowing it to survive in the environment and infect new cells.
Correct answer: A. Retrovirus
HIV belongs to a special class of virus known as retrovirus. Retroviruses are a type of virus that uses RNA as its genetic material. They are also unique in that they use an enzyme called reverse transcriptase to convert their RNA genome into DNA. This DNA is then integrated into the host cell's genome, where it can be transcribed and translated into viral proteins. Retroviruses are responsible for a number of diseases in humans and animals, including HIV/AIDS, leukemia, and lymphoma. HIV is a retrovirus that attacks the immune system, making it difficult for the body to fight off infection.
Correct answer: C. RNA
HIV is a retrovirus with a genome made of two single-stranded RNA molecules, about 9,700 nucleotides long. It carries genes that code for its essential proteins. After entering a host cell, its RNA is converted into DNA by reverse transcriptase and then integrated into the host genome so the virus can replicate.
Correct answer: A. Capsid
The capsule is an additional covering that surrounds the cell wall of some bacteria, providing protection against phagocytosis (engulfment by host cells), desiccation (drying out), Antibiotics and other antimicrobial agentsThe capsule is composed of polysaccharides (complex sugars) and can be found in both Gram-positive and Gram-negative bacteria.
Correct answer: B. Viroid
Viroids are small, circular RNA molecules that can infect plants. They lack a protein coat and do not encode proteins, relying on the host's cellular machinery for replication. Viroids are responsible for various plant diseases, disrupting normal growth and development
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