Question 1

Which of the following statements best describes the basis for the three-domain system of classification introduced by Carl Woese in 1978?

Accepted Answer

It is based on the sequence of ribosomal RNA (rRNA) genes.

Question 2

A microbiologist is trying to identify an unknown bacterial sample. She observes the cell's shape and arrangement under a microscope, performs a Gram stain, and tests for catalase activity. Which identification methods is she using?

Accepted Answer

Morphological, differential staining, and biochemical tests

Question 3

Which of the following is the correct order of taxonomic hierarchy from the most inclusive to the least inclusive?

Accepted Answer

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Question 4

A scientist is using ELISA to detect the presence of a specific bacterial antigen in a patient's serum. Which of the following best explains the principle behind ELISA?

Accepted Answer

It uses antibodies linked to an enzyme that produces a color change when the antigen is present.

Question 5

Which method would be most appropriate for distinguishing between two strains of the same bacterial species in a hospital outbreak investigation?

Accepted Answer

Phage typing

Question 6

A new microorganism is discovered that has a nucleus, mitochondria, and is multicellular. According to the three-domain system, to which domain does it belong?

Accepted Answer

Eukarya

Question 7

Which of the following best describes a phylogenetic tree?

Accepted Answer

A diagram showing the evolutionary relationships among various biological species based on similarities and differences in their genetic or physical characteristics.

Question 8

Which of the following is NOT a characteristic used to classify prokaryotes?

Accepted Answer

Ability to interbreed and produce fertile offspring

Question 9

A clinical laboratory is using Western blotting to confirm the presence of antibodies against HIV in a patient's serum. What is the main principle of this technique?

Accepted Answer

It detects specific proteins separated by gel electrophoresis using labeled antibodies.

Question 10

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

Accepted Answer

They do not have ribosomal RNA and are not composed of cells.

Question 11

A bacterial species is defined as a population of cells with similar characteristics. Which of the following methods would best help determine if two bacterial isolates belong to the same species?

Accepted Answer

Comparing their 16S rRNA gene sequences

Question 12

Which of the following is a correct example of scientific nomenclature for a bacterium?

Accepted Answer

$$Escherichia coli$$

Question 13

A hospital is experiencing an outbreak of a bacterial infection. The infection control team wants to determine if the strains isolated from different patients are genetically identical. Which method would be most appropriate?

Accepted Answer

DNA sequencing

Question 14

Which of the following best describes the use of fatty acid profiles in microbial identification?

Accepted Answer

They analyze the unique patterns of fatty acids in the cell membranes of microorganisms.

Question 15

A patient’s serum is mixed with a known bacterial antigen, and visible clumping is observed. Which serological technique is being used?

Accepted Answer

Agglutination test

Question 16

Which of the following statements about flow cytometry in microbiology is correct?

Accepted Answer

It is used to analyze the physical and chemical characteristics of cells as they flow in a fluid stream through a beam of light.

Question 17

Which of the following is a key difference between classification and identification of microorganisms?

Accepted Answer

Classification groups organisms based on evolutionary relationships, while identification determines the identity of an unknown organism.

Question 18

A laboratory is using PCR (polymerase chain reaction) to amplify a segment of bacterial DNA for identification. Which equation best represents the theoretical number of DNA copies after $$n$$ cycles, starting from a single DNA molecule?

Accepted Answer

$$N = 2^n$$

Question 19

Which of the following scenarios best illustrates the use of serological testing in distinguishing between bacterial species?

Accepted Answer

Using antibodies to detect specific surface antigens unique to each species

Question 20

A researcher is comparing the DNA sequences of two bacterial isolates. She finds that the 16S rRNA gene sequences are 99% identical. What does this suggest about the relationship between the two isolates?

Accepted Answer

They are likely to be the same species.

Classification and Identification of Microorganisms

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