BIOD
,171 – Essential Microbiology
Lab 4 Exam Questions & Answers (Latest 2025/2026)
Correct answer is marked
1. What is the main purpose of aseptic technique in microbiology?
A. Speed up bacterial growth
B. Prevent contamination of cultures
C. Kill all microorganisms
D. Improve microscope resolution
2. Which piece of equipment is used to sterilize media and instruments using pressure and
heat?
A. Incubator
B. Hot plate
C. Autoclave
D. Water bath
3. What temperature is commonly used in an autoclave for sterilization?
A. 80°C
B. 100°C
C. 121°C
D. 150°C
4. The flame of a Bunsen burner is used in aseptic technique primarily to:
A. Heat media
B. Create an updraft to reduce contamination
C. Kill all airborne bacteria
D. Dry glassware
5. Which microscope lens provides the greatest magnification?
,A. Scanning
B. Low power
C. High power
D. Oil immersion
6. What is the total magnification when using a 10× ocular lens and a 40× objective lens?
A. 40×
B. 100×
C. 400×
D. 1000×
7. Why is immersion oil used with the 100× objective lens?
A. To clean the lens
B. To reduce light refraction
C. To kill bacteria
D. To stain specimens
8. What type of microscope is most commonly used in microbiology labs?
A. Electron microscope
B. Stereo microscope
C. Bright-field microscope
D. Phase-contrast microscope
9. What is the correct order of focusing a microscope?
A. High power → low power
B. Low power → high power
C. Oil immersion → scanning
D. Ocular → condenser
10. What stain is used first in a Gram stain procedure?
, A. Safranin
B. Alcohol
C. Iodine
D. Crystal violet
11. Which reagent acts as a mordant in the Gram stain?
A. Crystal violet
B. Iodine
C. Safranin
D. Alcohol
12. What color do Gram-positive bacteria appear after staining?
A. Pink
B. Red
C. Purple
D. Colorless
13. What color do Gram-negative bacteria appear after staining?
A. Blue
B. Green
C. Purple
D. Pink
14. The alcohol step in Gram staining serves to:
A. Kill bacteria
B. Fix the cells
C. Decolorize the cells
D. Counterstain the cells
15. Which bacterial structure retains the crystal violet-iodine complex?
,171 – Essential Microbiology
Lab 4 Exam Questions & Answers (Latest 2025/2026)
Correct answer is marked
1. What is the main purpose of aseptic technique in microbiology?
A. Speed up bacterial growth
B. Prevent contamination of cultures
C. Kill all microorganisms
D. Improve microscope resolution
2. Which piece of equipment is used to sterilize media and instruments using pressure and
heat?
A. Incubator
B. Hot plate
C. Autoclave
D. Water bath
3. What temperature is commonly used in an autoclave for sterilization?
A. 80°C
B. 100°C
C. 121°C
D. 150°C
4. The flame of a Bunsen burner is used in aseptic technique primarily to:
A. Heat media
B. Create an updraft to reduce contamination
C. Kill all airborne bacteria
D. Dry glassware
5. Which microscope lens provides the greatest magnification?
,A. Scanning
B. Low power
C. High power
D. Oil immersion
6. What is the total magnification when using a 10× ocular lens and a 40× objective lens?
A. 40×
B. 100×
C. 400×
D. 1000×
7. Why is immersion oil used with the 100× objective lens?
A. To clean the lens
B. To reduce light refraction
C. To kill bacteria
D. To stain specimens
8. What type of microscope is most commonly used in microbiology labs?
A. Electron microscope
B. Stereo microscope
C. Bright-field microscope
D. Phase-contrast microscope
9. What is the correct order of focusing a microscope?
A. High power → low power
B. Low power → high power
C. Oil immersion → scanning
D. Ocular → condenser
10. What stain is used first in a Gram stain procedure?
, A. Safranin
B. Alcohol
C. Iodine
D. Crystal violet
11. Which reagent acts as a mordant in the Gram stain?
A. Crystal violet
B. Iodine
C. Safranin
D. Alcohol
12. What color do Gram-positive bacteria appear after staining?
A. Pink
B. Red
C. Purple
D. Colorless
13. What color do Gram-negative bacteria appear after staining?
A. Blue
B. Green
C. Purple
D. Pink
14. The alcohol step in Gram staining serves to:
A. Kill bacteria
B. Fix the cells
C. Decolorize the cells
D. Counterstain the cells
15. Which bacterial structure retains the crystal violet-iodine complex?
