Practice MDCAT Biology Easy MCQs with explanations — PMC, ETEA, NUMS entry test preparation.
Q1. A researcher extracts sap from an infected tobacco plant and passes it through a porcelain filter. Which organism would still be present in the filtrate?
Answer: Tobacco Mosaic Virus
Explanation: Viruses pass through filters that retain bacteria. Tobacco Mosaic Virus is the correct answer; bacteria like E. coli are trapped by such filters.
Q2. During the assembly of an Adenovirus particle, how many individual protein subunits or capsomeres are required to form its icosahedral capsid?
Answer: 252 capsomeres
Explanation: Adenovirus has 252 capsomeres. 162 is the count for Herpes virus, which is a common point of confusion for students.
Q3. Microscopic examination of a specific virus reveals a complex, brick-shaped symmetry. To which viral group does this pathogen most likely belong?
Answer: Brick-shaped
Explanation: Poxviruses like Smallpox are brick-shaped. Parvoviruses and Adenoviruses are icosahedral, representing different structural symmetries in virology.
Q4. A child presents with symptoms of infantile paralysis. The causative agent is an RNA virus characterized by which specific morphology?
Answer: Spherical RNA virus
Explanation: Polio virus is a spherical RNA virus. Paramyxoviruses are also RNA viruses but cause mumps/measles, not infantile paralysis.
Q5. Scientists discover an infectious agent that causes scrapie in sheep but lacks any detectable nucleic acids. What is the nature of this agent?
Answer: Protein only
Explanation: Prions are purely proteinaceous infectious particles. Viroids consist only of naked RNA, lacking the protein component found in prions.
Q6. In 1980, the World Health Organization declared the global eradication of a specific viral disease. Which virus was the target of this successful campaign?
Answer: Smallpox virus
Explanation: Smallpox was officially eradicated in 1980. Polio and Measles are still present globally, though vaccination efforts are extensive.
Q7. When comparing the size of different pathogens, which range correctly describes the typical diameter of most known viruses?
Answer: 20nm to 250nm
Explanation: Viruses range from 20nm to 250nm. Options in micrometers (µm) are incorrect as that is the size range for bacteria.
Q8. Analysis of a Herpes virus capsid reveals a specific number of capsomeres. How many capsomeres are present in this icosahedral virus?
Answer: 162 capsomeres
Explanation: Herpes virus has 162 capsomeres. 252 is the count for Adenovirus, which is the most frequent distractor for this fact.
Q9. During an experiment, a T4 bacteriophage fails to attach to an E. coli cell. Which structure is likely defective or missing?
Answer: Tail fibers
Explanation: Tail fibers are responsible for attachment to specific receptor sites; tail pins fail because they only assist in penetration.
Q10. In 1796, a young boy was inoculated with pus from a cowpox lesion to provide immunity. Which scientist performed this?
Answer: Edward Jenner
Explanation: Edward Jenner used cowpox to create the first vaccine; Louis Pasteur fails because he developed vaccines for rabies much later.
Q11. A botanist observes that tobacco leaf extract remains infectious even after passing through a Porcelain filter. Who first discovered this filterable nature?
Answer: Iwanowski
Explanation: Iwanowski demonstrated that TMV could pass through bacteria-proof filters; Stanley fails because he was the first to crystallize the virus.
Q12. A child in a rural area develops paralysis. The virus was likely ingested through contaminated water. What is the transmission route?
Answer: Fecal-oral route
Explanation: Poliovirus is primarily transmitted via the fecal-oral route; Hepatitis B fails because it is transmitted through blood or body fluids.
Q13. During the penetration phase of the lytic cycle, which enzyme is released by the phage to dissolve the bacterial cell wall?
Answer: Lysozyme
Explanation: Lysozyme is used by phages to digest the bacterial cell wall; Endonuclease fails because it cuts DNA inside the cell.
Q14. An electron micrograph reveals an icosahedral virus causing a respiratory infection. If it is an Adenovirus, how many capsomeres are present?
Answer: 252
Explanation: Adenoviruses have 252 capsomeres in their capsid; Herpesvirus is a tempting wrong choice as it has exactly 162 capsomeres.
Q15. A 5-year-old child develops swelling of the parotid glands and a generalized rash. These diseases are caused by which group?
Answer: Paramyxoviruses
Explanation: Mumps and Measles are both caused by paramyxoviruses; Rhinovirus fails because it is the primary cause of the common cold.
Q16. Which term best describes the stage of the viral life cycle where the phage tail fibers land on the E. coli surface?
Answer: Adsorption
Explanation: Adsorption is the first step where the virus attaches to the host; penetration fails because it involves the entry of DNA.
Q17. A scientist aims to prove that viruses are not merely small bacteria but chemical entities. Which researcher first successfully crystallized the Tobacco Mosaic Virus?
Answer: Wendell Stanley
Explanation: Stanley first crystallized TMV in 1935, proving viruses have a chemical nature. Iwanowski is tempting but he only demonstrated filterability.
Q18. A patient is diagnosed with a serum-borne viral infection of the liver. Laboratory tests confirm the virus has a DNA genome. Which virus is it?
Answer: Hepatitis B
Explanation: Hepatitis B is the only DNA virus among common hepatitis types. Hepatitis C is a tempting choice but it contains an RNA genome.
Q19. Microscopic examination of a virus reveals a tadpole-like structure with an icosahedral head and a contractile tail. Which virus is this?
Answer: T4 Bacteriophage
Explanation: T4 phages exhibit complex symmetry with a head and tail. TMV is tempting but it has simple helical symmetry without a tail.
Q20. A neurological condition in sheep called Scrapie is found to be caused by an agent containing no DNA or RNA. Identify the agent.
Answer: Prions
Explanation: Prions are purely proteinaceous and lack nucleic acids. Viroids are tempting but they are made of RNA and lack protein.
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