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NMCN Professional Exam Microbiology — practice by topic

Browse 38 questions across 1 Microbiology topics. Choose what you want to revise, then open a question to check its answer and worked solution.

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Microbiology topics

Bacteriology (38)

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Which material forms the cell wall of a bacterium?Read the answer and worked solution →In a Gram-positive bacterium, peptidoglycan accounts for what share of the cell wall?Read the answer and worked solution →What lies immediately outside the thin peptidoglycan wall of a Gram-negative bacterium?Read the answer and worked solution →How does an archaean cell wall differ from a bacterial one?Read the answer and worked solution →

Worked practice questions

Which material forms the cell wall of a bacterium?

  1. Peptidoglycan, a cross-linked polymer
  2. Cellulose, a plant-type wall polymer
  3. Chitin, the wall polymer of fungi
  4. Cholesterol, a membrane sterol lipid
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Correct answer: A. Peptidoglycan, a cross-linked polymer

1. The bacterial wall is built from peptidoglycan, polysaccharide chains cross-linked by unusual peptides. 2. Those peptides carry both L- and D-amino acids, which is what makes the wall a drug target. 3. Cellulose walls belong to plants, and chitin walls belong to fungi and insects, not to bacteria. 4. Cholesterol is a lipid, so it could never give the wall its rigid cross-linked mesh. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 22 "Prokaryotes: Bacteria and Archaea", section 22.2 Structure of Prokaryotes_

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In a Gram-positive bacterium, peptidoglycan accounts for what share of the cell wall?

  1. About 10 percent of the total wall
  2. Up to 90 percent of the total wall
  3. About 50 percent of the total wall
  4. Under 5 percent of the total wall
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Correct answer: B. Up to 90 percent of the total wall

1. Gram-positive organisms build a thick wall, and up to 90 percent of it is peptidoglycan. 2. Most of the remainder is made of acidic substances called teichoic acids. 3. The 10 percent figure belongs to Gram-negative bacteria, whose wall is only a few peptidoglycan layers thick. 4. That thickness difference is why the two groups respond differently to Gram staining. 5. Values of 50 percent and 5 percent match neither group. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 22 "Prokaryotes: Bacteria and Archaea", section 22.2 Structure of Prokaryotes_

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What lies immediately outside the thin peptidoglycan wall of a Gram-negative bacterium?

  1. A thick sheath of teichoic acids
  2. A capsule made of pure protein
  3. An envelope of lipopolysaccharides
  4. A second wall of pseudopeptidoglycan
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Correct answer: C. An envelope of lipopolysaccharides

1. A Gram-negative wall is only a few layers of peptidoglycan, about 10 percent of the total wall. 2. Surrounding it is an outer envelope containing lipopolysaccharides and lipoproteins. 3. That envelope is sometimes called a second lipid bilayer, although its chemistry differs from a plasma membrane. 4. Teichoic acids are a Gram-positive feature, so they cannot be the outer layer here. 5. Pseudopeptidoglycan is one of the four archaean wall types, not a bacterial layer. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 22 "Prokaryotes: Bacteria and Archaea", section 22.2 Structure of Prokaryotes_

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