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Microbiology — Practice Questions flashcards

6 of 40 questions free to study here · 9 topics · the whole deck is built into Willys

Multiple-choice practice questions, one best answer each, on Gram and acid-fast stains, growth and media, sterilization, viruses, immunity, infection control and antibiotic action.

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Practice deck · part of Microbiology for Health Sciences · written against: Standard nursing/allied-health microbiology course; OpenStax Microbiology, consulted as a reference; no text copied. Updated 2026-10-10.

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  1. Under the electron microscope, a cell shows a rigid wall, 70S ribosomes and DNA lying in an unenclosed region of the cytoplasm. Which kind of organism is it most likely to be?

    A) A mold
    B) A protozoan
    C) A yeast
    D) A bacterium
    D) A bacterium

    DNA in an unenclosed nucleoid plus 70S ribosomes marks a prokaryote. Yeasts and molds also have cell walls, but as eukaryotes they keep their DNA in a true nucleus and have 80S cytoplasmic ribosomes.
    Cell Structure
  2. Under ideal conditions a bacterium divides by binary fission every 20 minutes. Starting from one cell in the log phase, how many cells are present after 2 hours?

    A) 32
    B) 12
    C) 64
    D) 128
    C) 64

    2 hours contains 6 doubling times, so the count is 262^{6} = 64. Multiplying 2 by 6 gives 12, which treats growth as linear instead of exponential.
    Growth & Culture
  3. A heat-tolerant metal instrument must be made free of all microbial life, including bacterial endospores. Which method achieves this?

    A) Boiling it in water for several minutes
    B) Wiping it down with 70% alcohol
    C) Dry heat at 100 °C for one hour
    D) Steam under pressure in an autoclave
    D) Steam under pressure in an autoclave

    Moist heat under pressure, typically 121 °C at about 15 psi for at least 15 minutes, denatures proteins and kills even endospores, so it is sterilization. Alcohol does not kill endospores, and dry heat needs roughly 160–170 °C for one to two hours.
    Microbial Control
  4. An antifungal drug binds ergosterol in the cell membrane. Why does it damage fungal cells while mostly sparing human cells?

    A) Fungal cells lack a membrane-bound nucleus
    B) Human cells have a chitin wall that blocks it
    C) Human cell membranes use cholesterol instead
    D) Fungal cells have 70S cytoplasmic ribosomes
    C) Human cell membranes use cholesterol instead

    Ergosterol is the fungal counterpart of cholesterol, so a drug that targets it damages fungal membranes with less effect on human cells. Fungi are eukaryotes with a true nucleus, and chitin is found in fungal walls, not human cells.
    Fungi & Parasites
  5. A patient's serum contains a high level of IgM specific for a virus but very little specific IgG. What does this pattern most likely indicate?

    A) An infection with the virus many years ago
    B) Protection left by an old inactivated vaccine
    C) A recent or current infection with the virus
    D) Antibodies passed from the mother before birth
    C) A recent or current infection with the virus

    IgM is the first antibody made in a new infection, so a high specific IgM suggests a recent or current infection. A past infection or old vaccination would leave mainly IgG memory responses.
    Immunity & Vaccines
  6. A beta-lactam drug kills bacteria by blocking the cross-linking of peptidoglycan. What makes it selectively toxic to bacteria?

    A) Human cells have no peptidoglycan to build
    B) Human cells destroy the drug with beta-lactamase
    C) Human cells have 80S instead of 70S ribosomes
    D) Human cell membranes contain cholesterol
    A) Human cells have no peptidoglycan to build

    Beta-lactams inhibit the penicillin-binding proteins that cross-link peptidoglycan, and human cells have no cell wall at all. The 80S ribosome difference is real but explains the selectivity of protein-synthesis inhibitors, not wall inhibitors.
    Antimicrobials & Resistance

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About these cards

Review status: Second-reader reviewed, with corrections applied.

Checked against:

  • OpenStax Microbiology, consulted as a reference; no text copied.
  • Infection-control points checked against CDC hand hygiene and C. difficile guidance for health care settings (reference only; all wording is original).
  • Original questions written for this deck in the style of an intro microbiology final exam; no official, textbook or question-bank items were copied. Medication amounts are deliberately omitted, and no treatment advice is given.

These are independent study notes written for Willys. They are not official exam material, may contain mistakes, and are no substitute for your course, your teacher or the exam owner's own publications. Found an error? Tell us — corrections ship as a new version of the deck.

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