Q: Which equation correctly calculates the total magnification power of a compound light microscope?

Total magnification $$= \text{Objective lens power} \times \text{Eyepiece power}$$

Q: Which formula is used to calculate colony-forming units (CFUs) per 1 mL of sample in a standard plate count?

CFUs per 1 mL $$= \frac{\text{Number of colonies}}{\text{Volume plated (mL)} \times \text{Dilution factor}}$$

Question 1

Which of the following best describes the purpose of using oil immersion with the 1000X objective lens on a compound light microscope?

Accepted Answer

To reduce light refraction and improve resolution by matching the refractive index between the lens and the slide.

Question 2

A student is preparing a bacterial smear for staining but forgets to heat-fix the slide. Which outcome is most likely?

Accepted Answer

The bacteria will wash off during staining, resulting in little to no cells visible.

Question 3

Which equation correctly calculates the total magnification power of a compound light microscope?

Accepted Answer

Total magnification $$= 	ext{Objective lens power} 	imes 	ext{Eyepiece power}$$

Question 4

During a streak-plate technique, which step is critical for diluting the number of cells between each section to achieve isolated colonies?

Accepted Answer

Flaming the loop between streaking each section.

Question 5

Which of the following best distinguishes a differential stain from a simple stain?

Accepted Answer

A differential stain differentiates between types of bacteria based on cellular components, while a simple stain colors all cells the same.

Question 6

A Gram stain is performed in the following order: crystal violet, iodine, alcohol, safranin. What is the function of the alcohol step?

Accepted Answer

It decolorizes Gram-negative cells by dissolving the outer membrane.

Question 7

Which formula is used to calculate colony-forming units (CFUs) per 1 mL of sample in a standard plate count?

Accepted Answer

CFUs per 1 mL $$= \frac{	ext{Number of colonies}}{	ext{Volume plated (mL)} 	imes 	ext{Dilution factor}}$$

Question 8

A microbiologist is testing the effectiveness of an antiseptic and a disinfectant against Gram-positive and Gram-negative bacteria. Which statement is most accurate?

Accepted Answer

Disinfectants tend to be more effective against Gram-positive bacteria because Gram-negative bacteria have an outer membrane that can block many agents.

Question 9

Which of the following best describes selective toxicity in antimicrobial agents?

Accepted Answer

The agent targets microbial cells without harming host cells.

Question 10

A catalase test is performed on two unknown Gram-positive bacteria. One produces bubbles when hydrogen peroxide is added, the other does not. What does this indicate?

Accepted Answer

The bubble-producing bacterium is likely a staphylococcus, while the other is likely a streptococcus.

Question 11

Which of the following is the correct formula for calculating the dilution factor when mixing a sample with a diluent?

Accepted Answer

Dilution factor $$= \frac{	ext{Total volume (sample + diluent)}}{	ext{Volume of sample}}$$

Question 12

Which of the following best describes the mechanism of action for a sterilant?

Accepted Answer

It kills all forms of microbial life, including spores.

Question 13

A student observes a slide under 1000X magnification and sees rod-shaped bacteria arranged in chains. Which term best describes this morphology?

Accepted Answer

Streptobacillus

Question 14

Which of the following is a common mistake that can lead to a false negative result in the oxidase test?

Accepted Answer

Reading the test result after more than 60 seconds.

Question 15

Which of the following best explains why acid-fast staining is medically significant?

Accepted Answer

It detects mycobacteria, such as those causing tuberculosis, which have waxy cell walls.

Question 16

Which of the following is true regarding the interpretation of plates in a standard plate count?

Accepted Answer

A plate with 300 colonies is countable.

Question 17

Which of the following best describes the function of a bacterial capsule?

Accepted Answer

It increases virulence by protecting bacteria from phagocytosis.

Question 18

Which of the following statements about the oxidase test is correct?

Accepted Answer

It detects the presence of cytochrome c oxidase in Gram-negative bacteria.

Question 19

A student is asked to identify the correct labeling procedure for microbiology media. Which of the following is best practice?

Accepted Answer

Label the bottom of the plate with the organism name, date, and your initials.

Microbiology Lab Exam 1: Comprehensive Study Guide (Labs 1-12, 14-16, 20, 25)

Study Guide - Practice Questions

Study Guide - Flashcards