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Microbiology: Microbial Metabolism Flashcards

7 cards from real AP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Which metabolic product of mixed acid fermentation is detected by the methyl red (MR) test?

    Answer: Strong organic acids (lactic, acetic, formic)

    The MR test detects a significant drop in pH caused by the strong mixed acids (lactic, acetic, formic, succinic) produced by organisms like E. coli.

  2. During oxidative phosphorylation, what directly drives the synthesis of ATP by ATP synthase?

    Answer: Flow of protons down their electrochemical gradient through ATP synthase

    The proton motive force drives protons through the Fo subunit of ATP synthase, causing conformational changes in the F1 subunit that synthesize ATP from ADP and Pi.

  3. Methanogenesis, carried out by archaea, is best described as:

    Answer: Anaerobic respiration using CO2 as an electron acceptor to produce CH4

    Methanogens use CO2 (or other one-carbon compounds) as terminal electron acceptors in anaerobic respiration, reducing them to methane (CH4) using H2 or other electron donors.

  4. A researcher inhibits the F0 subunit of ATP synthase with oligomycin. What will happen to the proton gradient across the membrane?

    Answer: The gradient will increase as protons can no longer flow back through ATP synthase

    Blocking ATP synthase prevents protons from re-entering via this channel, so the proton motive force increases as the ETC continues pumping protons outward.

  5. The Voges-Proskauer (VP) test distinguishes bacteria that produce which fermentation end product?

    Answer: Acetoin (acetylmethylcarbinol)

    The VP test detects acetoin, which is oxidized to diacetyl in the presence of KOH and a catalyst, producing a red color when positive.

  6. Why do obligate anaerobes die in the presence of oxygen?

    Answer: They lack enzymes like superoxide dismutase and catalase to detoxify reactive oxygen species

    Obligate anaerobes lack superoxide dismutase and/or catalase, so toxic reactive oxygen species like superoxide (O2⁻) and H2O2 accumulate and damage cellular components.

  7. Which statement correctly describes the role of ubiquinone (coenzyme Q) in the electron transport chain?

    Answer: It is a mobile lipid-soluble electron carrier that shuttles electrons between Complexes I/II and Complex III

    Ubiquinone is a small, lipid-soluble molecule that diffuses within the inner membrane, collecting electrons from Complexes I and II and delivering them to Complex III.