,BIOD 171 Essential Microbiology Lab 3: Exam Questions & Answers
1. What is the primary purpose of aseptic technique?
A. To speed up bacterial growth
B. To prevent contamination of cultures and environment ✓
C. To make media more nutritious
D. To sterilize loops without a flame
2. Which of the following is the correct sequence for Gram staining?
A. Crystal violet → Iodine → Decolorizer → Safranin ✓
B. Safranin → Iodine → Decolorizer → Crystal violet
C. Crystal violet → Decolorizer → Iodine → Safranin
D. Iodine → Crystal violet → Safranin → Decolorizer
3. What is the mordant in the Gram stain?
A. Crystal violet
B. Safranin
C. Iodine ✓
D. Alcohol
4. After decolorization in the Gram stain, Gram-negative bacteria appear:
A. Purple
B. Colorless ✓
C. Pink/Red
D. Blue
5. The counterstain in the Gram stain is:
A. Crystal violet
B. Iodine
C. Decolorizer
D. Safranin ✓
6. A pure culture is best defined as:
A. A culture containing multiple species
B. A culture containing only one species of microorganism ✓
C. A culture on solid media
D. A culture in liquid media
,7. What is the purpose of heat fixation during smear preparation?
A. To kill the bacteria and adhere them to the slide ✓
B. To stain the bacteria
C. To increase motility
D. To sterilize the slide
8. Which objective lens provides the highest total magnification on a standard light
microscope (with 10x oculars)?
A. 4x (40x total)
B. 10x (100x total)
C. 40x (400x total)
D. 100x oil immersion (1000x total) ✓
9. Acid-fast bacteria retain which primary stain?
A. Methylene blue
B. Crystal violet
C. Carbol fuchsin ✓
D. Safranin
10. Which reagent is used to decolorize acid-fast stains?
A. Water
B. Acid-alcohol ✓
C. Iodine
D. Ethanol only
11. In the Kinyoun acid-fast stain, what is the role of phenol?
A. Counterstain
B. Decolorizer
C. Mordant
D. Helps the primary stain penetrate the waxy cell wall ✓
12. After acid-fast staining, non-acid-fast bacteria appear:
A. Red
B. Blue ✓
C. Purple
D. Green
13. What is the shape and Gram reaction of Bacillus subtilis?
A. Gram-positive cocci
B. Gram-negative rods
, C. Gram-positive rods ✓
D. Gram-negative cocci
14. What is the shape and Gram reaction of Escherichia coli?
A. Gram-positive cocci
B. Gram-negative rods ✓
C. Gram-positive rods
D. Gram-negative cocci
15. Staphylococcus aureus appears as:
A. Gram-negative rods
B. Gram-positive cocci in clusters ✓
C. Gram-positive rods in chains
D. Gram-negative diplococci
16. The term "colony morphology" refers to:
A. Genetic makeup of bacteria
B. Physical characteristics of a bacterial colony on agar ✓
C. Staining properties
D. Motility patterns
17. Which of the following is NOT a typical colony morphology characteristic?
A. Color
B. Size
C. Shape
D. Gram stain reaction ✓
18. A bacterial colony that is smooth, moist, and entire at the margin is described as:
A. Filamentous
B. Rhizoid
C. Circular and smooth ✓
D. Irregular and dry
19. What is the purpose of the quadrant streak method?
A. To increase bacterial growth rate
B. To isolate individual colonies from a mixed culture ✓
C. To stain bacteria directly on the plate
D. To preserve bacterial stocks
20. In the quadrant streak, the loop is flamed:
A. Only at the start
1. What is the primary purpose of aseptic technique?
A. To speed up bacterial growth
B. To prevent contamination of cultures and environment ✓
C. To make media more nutritious
D. To sterilize loops without a flame
2. Which of the following is the correct sequence for Gram staining?
A. Crystal violet → Iodine → Decolorizer → Safranin ✓
B. Safranin → Iodine → Decolorizer → Crystal violet
C. Crystal violet → Decolorizer → Iodine → Safranin
D. Iodine → Crystal violet → Safranin → Decolorizer
3. What is the mordant in the Gram stain?
A. Crystal violet
B. Safranin
C. Iodine ✓
D. Alcohol
4. After decolorization in the Gram stain, Gram-negative bacteria appear:
A. Purple
B. Colorless ✓
C. Pink/Red
D. Blue
5. The counterstain in the Gram stain is:
A. Crystal violet
B. Iodine
C. Decolorizer
D. Safranin ✓
6. A pure culture is best defined as:
A. A culture containing multiple species
B. A culture containing only one species of microorganism ✓
C. A culture on solid media
D. A culture in liquid media
,7. What is the purpose of heat fixation during smear preparation?
A. To kill the bacteria and adhere them to the slide ✓
B. To stain the bacteria
C. To increase motility
D. To sterilize the slide
8. Which objective lens provides the highest total magnification on a standard light
microscope (with 10x oculars)?
A. 4x (40x total)
B. 10x (100x total)
C. 40x (400x total)
D. 100x oil immersion (1000x total) ✓
9. Acid-fast bacteria retain which primary stain?
A. Methylene blue
B. Crystal violet
C. Carbol fuchsin ✓
D. Safranin
10. Which reagent is used to decolorize acid-fast stains?
A. Water
B. Acid-alcohol ✓
C. Iodine
D. Ethanol only
11. In the Kinyoun acid-fast stain, what is the role of phenol?
A. Counterstain
B. Decolorizer
C. Mordant
D. Helps the primary stain penetrate the waxy cell wall ✓
12. After acid-fast staining, non-acid-fast bacteria appear:
A. Red
B. Blue ✓
C. Purple
D. Green
13. What is the shape and Gram reaction of Bacillus subtilis?
A. Gram-positive cocci
B. Gram-negative rods
, C. Gram-positive rods ✓
D. Gram-negative cocci
14. What is the shape and Gram reaction of Escherichia coli?
A. Gram-positive cocci
B. Gram-negative rods ✓
C. Gram-positive rods
D. Gram-negative cocci
15. Staphylococcus aureus appears as:
A. Gram-negative rods
B. Gram-positive cocci in clusters ✓
C. Gram-positive rods in chains
D. Gram-negative diplococci
16. The term "colony morphology" refers to:
A. Genetic makeup of bacteria
B. Physical characteristics of a bacterial colony on agar ✓
C. Staining properties
D. Motility patterns
17. Which of the following is NOT a typical colony morphology characteristic?
A. Color
B. Size
C. Shape
D. Gram stain reaction ✓
18. A bacterial colony that is smooth, moist, and entire at the margin is described as:
A. Filamentous
B. Rhizoid
C. Circular and smooth ✓
D. Irregular and dry
19. What is the purpose of the quadrant streak method?
A. To increase bacterial growth rate
B. To isolate individual colonies from a mixed culture ✓
C. To stain bacteria directly on the plate
D. To preserve bacterial stocks
20. In the quadrant streak, the loop is flamed:
A. Only at the start
