Question 1

Which of the following statements best explains why Louis Pasteur's swan-neck flask experiment was critical in disproving spontaneous generation?

Accepted Answer

It allowed air to enter the flask but prevented microbes from reaching the broth, showing that microbes come from the environment, not spontaneous generation.

Question 2

A scientist isolates a unicellular organism with no nucleus, a cell wall lacking peptidoglycan, and membrane lipids with ether bonds. To which domain does this organism most likely belong?

Accepted Answer

Domain Archaea

Question 3

Which of the following best describes the function of teichoic acids in Gram-positive bacteria?

Accepted Answer

They help anchor the peptidoglycan layer to the plasma membrane and contribute to cell wall stability.

Question 4

A patient is diagnosed with tuberculosis. Which staining technique would be most appropriate to confirm the presence of Mycobacterium tuberculosis in a sputum sample, and why?

Accepted Answer

Acid-fast stain, because Mycobacterium has mycolic acid in its cell wall that retains carbolfuchsin after acid-alcohol decolorization.

Question 5

Which of the following best explains why immersion oil is used with the 100X objective lens in light microscopy?

Accepted Answer

It has the same refractive index as glass, reducing light refraction and increasing resolution.

Question 6

Which of the following is a correct example of binomial nomenclature for a yeast used in baking and brewing?

Accepted Answer

Saccharomyces cerevisiae

Question 7

A solution is made by dissolving 5 g of NaCl in 100 mL of water. Which component is the solute and which is the solvent?

Accepted Answer

NaCl is the solute; water is the solvent.

Question 8

Which of the following best describes the chemical reaction of hydrolysis?

Accepted Answer

A water molecule is used to break a covalent bond in a polymer.

Question 9

Which of the following statements about the pH scale is correct?

Accepted Answer

A solution with pH 7 has equal concentrations of $$\mathrm{H^+}$$ and $$\mathrm{OH^-}$$ ions.

Question 10

Which of the following best explains why proteins denature at high temperatures?

Accepted Answer

High temperatures disrupt hydrogen bonds and other interactions, causing the protein to lose its three-dimensional structure.

Question 11

A bacterial cell is observed to have a thick peptidoglycan layer, teichoic acids, and no outer membrane. Which Gram stain result would you expect, and what color would the cell appear after staining?

Accepted Answer

Gram-positive; purple

Question 12

Which of the following best describes the arrangement of phospholipids in the plasma membrane of bacteria?

Accepted Answer

Hydrophilic heads face the cytoplasm and the external environment, while hydrophobic tails are in the center.

Question 13

Which of the following is a correct description of the function of bacterial fimbriae?

Accepted Answer

They are used for attachment to surfaces, including human tissues.

Question 14

Which of the following best explains why antibiotics that target peptidoglycan are ineffective against Archaea?

Accepted Answer

Archaea lack peptidoglycan in their cell walls, so antibiotics targeting peptidoglycan have no effect.

Question 15

A microbiologist observes a chain of round bacterial cells under the microscope. Which term best describes this arrangement?

Accepted Answer

Streptococcus

Question 16

Which of the following best describes the process of germination in bacterial endospores?

Accepted Answer

An endospore returns to a vegetative state when conditions become favorable.

Question 17

Which of the following best explains why viruses are not classified within the three domains of life?

Accepted Answer

They are subcellular parasites that require host cells for reproduction and lack cellular structure.

Question 18

Which of the following is a correct statement about the relationship between DNA, RNA, and proteins in gene expression?

Accepted Answer

DNA is transcribed into RNA, which is then translated into protein.

Question 19

A sample contains a mixture of bacteria, some of which have a thick peptidoglycan layer and others with a thin peptidoglycan layer and an outer membrane. After performing a Gram stain, what would you expect to observe under the microscope?

Accepted Answer

Cells with thick peptidoglycan appear purple; cells with thin peptidoglycan and an outer membrane appear pink.

Microbiology Study Guide: Chapters 1–4 (BIO 255, Spring 2026)

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