Question 1

Which of the following best explains why Gram-positive bacteria retain the crystal violet stain during the Gram staining procedure?

Accepted Answer

Their thick peptidoglycan layer traps the crystal violet-iodine complex, preventing it from being washed out by alcohol.

Question 2

A clinical sample is stained using the acid-fast method. Rod-shaped bacteria appear red, while other cells are blue. What is the most likely identity of the red rods?

Accepted Answer

Mycobacterium species

Question 3

Which structure is responsible for the motility of bacteria and is visualized using a mordant and carbolfuchsin stain?

Accepted Answer

Flagella

Question 4

Why are drugs that target cell wall synthesis, such as penicillin, generally effective against bacteria but not human cells?

Accepted Answer

Bacterial cell walls contain peptidoglycan, which is absent in human cells.

Question 5

A bacterium is observed to have a thick, organized, and firmly attached glycocalyx. Which of the following is a likely consequence of this structure?

Accepted Answer

Increased resistance to phagocytosis by host immune cells

Question 6

Which of the following statements correctly differentiates prokaryotic and eukaryotic cells?

Accepted Answer

Prokaryotes have a single circular chromosome not enclosed in a membrane, while eukaryotes have paired chromosomes within a nuclear membrane.

Question 7

Which of the following best describes the arrangement and shape of Streptococcus bacteria?

Accepted Answer

Chains of spherical cells

Question 8

A patient is infected with a bacterium that is resistant to penicillin due to the absence of a cell wall. Which genus is most likely responsible?

Accepted Answer

Mycoplasma

Question 9

Which of the following is a function of bacterial fimbriae?

Accepted Answer

Attachment to surfaces

Question 10

During Gram staining, what is the primary function of the iodine step?

Accepted Answer

To act as a mordant and form a complex with crystal violet

Question 11

Which of the following best explains why Gram-negative bacteria are more resistant to certain antibiotics than Gram-positive bacteria?

Accepted Answer

They possess an outer membrane that restricts entry of many drugs.

Question 12

Which of the following is true regarding endospore staining?

Accepted Answer

Endospores appear green within red or pink cells after staining with malachite green and safranin.

Question 13

Which of the following cell wall components is unique to Gram-negative bacteria and contributes to their toxicity?

Accepted Answer

Lipopolysaccharide (LPS)

Question 14

A scientist observes a bacterium with a single flagellum at one end. What is the correct term for this flagellar arrangement?

Accepted Answer

Monotrichous

Question 15

Which of the following best describes the effect of lysozyme on bacterial cells?

Accepted Answer

It hydrolyzes bonds in peptidoglycan, leading to cell lysis.

Question 16

Which of the following is a distinguishing feature of Archaea cell walls compared to Bacteria?

Accepted Answer

Archaea cell walls contain pseudomurein and lack NAM and D-amino acids.

Question 17

Which of the following best explains why protoplasts and spheroplasts are susceptible to osmotic lysis?

Accepted Answer

They lack a cell wall, so they cannot withstand changes in osmotic pressure.

Question 18

Which of the following is a correct sequence of steps in the Gram staining procedure?

Accepted Answer

Crystal violet, iodine, alcohol, safranin

Question 19

Which of the following is a function of the extracellular polymeric substance (EPS) in bacterial biofilms?

Accepted Answer

It helps bacteria adhere to surfaces and protects them from environmental stress.

Question 20

A bacterium is observed to have multiple flagella distributed over its entire surface. What is the correct term for this arrangement?

Accepted Answer

Peritrichous

Microscopy, Staining, and Cell Structure in Microbiology

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