Question 1

Which of the following best describes the main structural difference between Gram-positive and Gram-negative bacterial cell walls?

Accepted Answer

Gram-positive bacteria have a thick peptidoglycan layer and no outer membrane, while Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharide.

Question 2

A patient is diagnosed with a bacterial infection caused by a species that forms endospores. Which of the following statements about endospores is correct?

Accepted Answer

Endospores are highly resistant to heat, drying, and chemicals, allowing bacteria to survive harsh conditions for extended periods.

Question 3

Which of the following best explains why negative staining is useful for visualizing bacterial capsules?

Accepted Answer

Negative stains do not bind to the capsule, creating a clear halo around the cell against a dark background.

Question 4

A microbiologist is using a phase-contrast microscope to observe a living bacterial culture. What is the main advantage of this technique?

Accepted Answer

It allows observation of living cells in their natural state without staining, preserving their motility and behavior.

Question 5

Which of the following is a function of the bacterial glycocalyx?

Accepted Answer

It aids in attachment to surfaces and formation of biofilms, and can protect bacteria from phagocytosis.

Question 6

A bacterium is observed to move toward a chemical attractant. Which structure is primarily responsible for this movement, and what is the mechanism?

Accepted Answer

Flagella, which rotate using an ion gradient to propel the cell in runs and tumbles.

Question 7

Which of the following statements about bacterial ribosomes is correct?

Accepted Answer

Bacterial ribosomes are 70S, composed of a 50S large subunit and a 30S small subunit.

Question 8

Which of the following best describes the composition and function of peptidoglycan in bacterial cell walls?

Accepted Answer

Peptidoglycan is composed of repeating disaccharide units (NAG and NAM) cross-linked by peptide chains, providing structural support and shape.

Question 9

A Gram-negative bacterium is more resistant to certain antibiotics than a Gram-positive bacterium. Which feature contributes most to this resistance?

Accepted Answer

The presence of an outer membrane containing lipopolysaccharide and porin proteins, which act as a barrier to many antibiotics.

Question 10

Which of the following is true regarding the genetic material of bacteria and archaea?

Accepted Answer

Their genetic material is typically a single, circular DNA molecule located in the nucleoid region of the cytoplasm.

Question 11

Which of the following best explains why mycoplasmas are resistant to antibiotics that target cell wall synthesis?

Accepted Answer

Mycoplasmas lack a cell wall and instead have sterols in their cell membrane for stability.

Question 12

Which of the following is a unique feature of archaeal cell walls compared to bacterial cell walls?

Accepted Answer

Archaeal cell walls lack peptidoglycan and may contain pseudopeptidoglycan or protein.

Question 13

A clinical sample is stained with crystal violet and safranin. The cells appear pink under the microscope. What can you conclude about the cell wall structure?

Accepted Answer

The cells are Gram-negative, with a thin peptidoglycan layer and an outer membrane.

Question 14

Which of the following best describes the function of bacterial inclusion bodies?

Accepted Answer

They store nutrients or other materials for later use by the cell.

Question 15

A bacterium is observed to have periplasmic flagella (axial filaments). Which type of bacterium is this most likely to be, and what is the significance of this structure?

Accepted Answer

A spirochete; the periplasmic flagella allow the cell to move in a corkscrew motion through viscous environments.

Question 16

Which of the following best explains why biofilms are difficult to eradicate from medical devices?

Accepted Answer

Biofilms are complex communities of bacteria encased in a protective glycocalyx, making them resistant to antibiotics and immune responses.

Question 17

Which of the following equations best represents the relationship between total magnification ($$M_{total}$$), objective lens magnification ($$M_{obj}$$), and ocular lens magnification ($$M_{ocular}) in $$light microscopy?

Accepted Answer

$$M_{total} = M_{obj} 	imes M_{ocular}$$

Question 18

A researcher is studying a bacterium that survives in extremely high salt concentrations. Which group is this organism most likely to belong to?

Accepted Answer

Archaea, specifically halophiles.

Question 19

Which of the following best describes the role of porin proteins in the outer membrane of Gram-negative bacteria?

Accepted Answer

They form channels that allow the passive diffusion of small molecules across the outer membrane.

Bacteria and Archaea: Structure, Classification, and Microscopy

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