Question 1

Which part of the compound microscope is primarily responsible for adjusting the amount of light that reaches the specimen?

Accepted Answer

The iris diaphragm

Question 2

If you are using a 40x objective lens and a 10x ocular lens, what is the total magnification?

Accepted Answer

$$40 	imes 10 = 400$$

Question 3

Which of the following is NOT a reason for using oil immersion with the 100x objective lens?

Accepted Answer

To prevent the lens from touching the slide

Question 4

Why is turbidity used as an indicator of microbial growth in liquid media?

Accepted Answer

Turbidity is caused by the scattering of light by microbial cells

Question 5

During aseptic technique, which step is most critical to prevent contamination of sterile media?

Accepted Answer

Flaming the loop before and after use

Question 6

What is the main difference between a simple stain and a differential stain?

Accepted Answer

Differential stains distinguish between different types of bacteria

Question 7

Which of the following best describes the principle of a negative stain?

Accepted Answer

The stain colors the background, leaving cells unstained

Question 8

Why do Gram-positive bacteria retain the crystal violet stain during the Gram stain procedure?

Accepted Answer

They have a thick peptidoglycan layer that traps the stain

Question 9

Which step in the Gram stain procedure is responsible for differentiating Gram-positive from Gram-negative bacteria?

Accepted Answer

Decolorization with alcohol or acetone

Question 10

A patient sample is stained using the acid-fast technique. The cells appear red under the microscope. What does this indicate?

Accepted Answer

The cells are acid-fast positive, likely Mycobacterium species

Question 11

Which chemical is used as a decolorizer in the acid-fast stain procedure?

Accepted Answer

Acid-alcohol

Question 12

What is the primary function of a bacterial capsule?

Accepted Answer

To protect the cell from phagocytosis

Question 13

Which staining technique would you use to visualize bacterial endospores?

Accepted Answer

Schaeffer-Fulton stain

Question 14

A microbiologist observes rod-shaped bacteria with a thick capsule under the microscope. Which staining method would best highlight the capsule?

Accepted Answer

Capsule stain

Question 15

Which of the following best explains why endospores are resistant to harsh environmental conditions?

Accepted Answer

Endospores contain dipicolinic acid and a tough spore coat

Question 16

A sample contains both motile and non-motile bacteria. Which method would best determine motility?

Accepted Answer

Wet mount preparation

Question 17

Which of the following equations correctly represents the calculation for resolving power ($$R) of a $$microscope?

Accepted Answer

$$R = \frac{0.61 	imes \lambda}{NA}$$

Question 18

During a Gram stain, a student forgets to add iodine. What is the most likely result?

Accepted Answer

Gram-positive cells may lose the crystal violet and appear pink

Question 19

Which of the following is a common error that can lead to false acid-fast negative results?

Accepted Answer

Insufficient staining time with carbol fuchsin

Question 20

A clinical sample is suspected to contain Mycobacterium tuberculosis. Which staining technique should be used to confirm its presence?

Accepted Answer

Acid-fast stain

BIOL 2117L Microbiology Midterm Exam Study Guide: Microscopy, Staining, and Microbial Techniques

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