Q: What is the total magnification when using a compound microscope with a 40x objective lens and a 10x ocular lens?

Total magnification = $$40 \times 10 = 400x$$

Question 1

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

Accepted Answer

Their cell wall is composed of a thick layer of peptidoglycan, which acts as a sponge for the dye.

Question 2

A student prepares a bacterial smear that is too thick. What is the most likely consequence when viewing the slide under a microscope after staining?

Accepted Answer

The bacteria will appear in clumps, making it difficult to observe their true morphology.

Question 3

During the Gram stain procedure, which step is responsible for differentiating Gram-positive from Gram-negative bacteria?

Accepted Answer

Applying the decolorizing agent (95% ethyl alcohol).

Question 4

What is the total magnification when using a compound microscope with a 40x objective lens and a 10x ocular lens?

Accepted Answer

Total magnification = $$40 	imes 10 = 400x$$

Question 5

Why must the inoculating loop be cooled for 15 seconds after sterilization before transferring bacteria?

Accepted Answer

To avoid killing the bacteria during transfer.

Question 6

Which of the following is a distinguishing feature of Gram-negative bacterial cell walls?

Accepted Answer

An outer lipid bilayer membrane containing lipopolysaccharides.

Question 7

A microbiologist observes a colony with a spreading edge and a shiny surface. Which characteristics are most likely responsible for these features?

Accepted Answer

Motility and presence of a capsule or slime layer.

Question 8

What is the primary purpose of using bibulous paper after staining a bacterial smear?

Accepted Answer

To remove excess stain without detaching bacteria from the slide.

Question 9

Which step in the preparation of a thin smear is essential for maintaining the native shape and arrangement of bacteria?

Accepted Answer

Allowing the smear to air dry before heat fixation.

Question 10

A colony of Proteus mirabilis is identified by its smooth, grey, large, and circular ring appearance. What real-world application does this identification have?

Accepted Answer

Diagnosing urinary tract infections in patients.

Question 11

Why is it important to sterilize both the inoculating loop and media before transferring bacteria in a laboratory setting?

Accepted Answer

To prevent cross-contamination and ensure only the desired bacteria are cultured.

Question 12

Which of the following best describes the function of the condenser in a compound microscope?

Accepted Answer

It concentrates light from the source into a narrow beam focused on the specimen.

Question 13

A student is using the coarse focus knob with the high power objective lens. What is the most likely risk?

Accepted Answer

The slide could collide with the objective lens, potentially damaging both.

Question 14

Which of the following media types would show growth as cloudiness or turbidity?

Accepted Answer

Liquid broth

Question 15

What is the main reason for performing a three-way streak plate technique on a mixed culture?

Accepted Answer

To isolate individual colonies of each species for identification.

Question 16

Which of the following statements about colony morphology is correct?

Accepted Answer

Colony morphology is determined by genetics but can be influenced by environmental conditions.

Question 17

In the Gram stain procedure, what is the role of the mordant iodine?

Accepted Answer

It crystalizes the crystal violet dye, trapping it in the peptidoglycan layer of Gram-positive cells.

Question 18

Which of the following best describes a pure culture in microbiology?

Accepted Answer

A culture containing only one bacterial species.

Question 19

A microbiologist observes a colony with a red pigment. Which species is most likely responsible for this coloration?

Accepted Answer

Serratia marcescens

Question 20

Which of the following best explains why all cells in a bacterial colony are genetically identical?

Accepted Answer

They originate from a single progenitor cell and divide by binary fission.

Bacterial Cell Structure, Staining, and Laboratory Techniques

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