UNE MICRO LAB FINAL EXAM QUESTIONS AND ANSWERS
WITH COMPLETE SOLUTIONS VERIFIED GRADED A++ LATEST
UPDATE 2025/2026
Microbiology Lab Final Exam: 100 Questions & Answers
1. What is the primary purpose of aseptic technique?
A) To make the lab work faster
B) To prevent contamination of cultures and the environment
C) To sterilize all equipment
D) To grow bacteria more efficiently
2. The lens of a microscope that is closest to the specimen is called
the:
A) Ocular lens
B) Objective lens
C) Condenser lens
D) Iris diaphragm
3. What is the total magnification when using the 100X oil immersion
objective with a standard 10X ocular lens?
A) 100X
B) 1000X
C) 400X
D) 2000X
4. Immersion oil is used with the 100X objective to:
A) Sterilize the lens
B) Increase the light refraction, improving resolution
C) Clean the slide
D) Decrease the magnification
,5. A medium whose exact chemical composition is known is called a:
A) Complex medium
B) Selective medium
C) Defined (Synthetic) medium
D) Differential medium
6. Mannitol Salt Agar (MSA) is both selective and differential. It is
selective for:
A) Gram-negative bacteria
B) Gram-positive bacteria, specifically Staphylococci
C) Lactose fermenters
D) Anaerobic bacteria
7. A bacterial colony that appears with a green, metallic sheen on
Eosin Methylene Blue (EMB) agar is indicative of:
A) Staphylococcus aureus
B) Pseudomonas aeruginosa
C) Escherichia coli
D) Proteus vulgaris
8. The process of killing all microorganisms, including bacterial
endospores, is called:
A) Disinfection
B) Antisepsis
C) Sanitization
D) Sterilization
9. Which of the following is the most resistant form of life?
A) Fungal spores
B) Protozoan cysts
,C) Bacterial endospores
D) Enveloped viruses
10. The standard autoclaving conditions for sterilization are:
A) 121°C at 15 psi for 15-20 minutes
B) 100°C for 10 minutes
C) 160°C for 2 hours
D) 71°C for 15 seconds
11. The method that provides a countable number of separate
colonies on an agar plate from a liquid culture is the:
A) Streak plate method
B) Pour plate method
C) Spread plate method
D) Broth dilution method
12. The purpose of the quadrant streak method is to:
A) Determine oxygen requirements
B) Observe colony pigmentation
C) Isolate pure cultures
D) Increase bacterial growth
13. A cloudy appearance in a liquid broth culture indicates:
A) Contamination
B) Bacterial growth
C) Sterility
D) A lack of nutrients
14. In a Gram stain, what is the function of the decolorizer (usually
alcohol/acetone)?
A) To fix the bacteria to the slide
, B) To stain Gram-negative cells
C) To remove the primary stain from Gram-negative cells
D) To stain Gram-positive cells
15. Gram-positive bacteria stain purple because:
A) They have a thin peptidoglycan layer
B) They have an outer membrane
C) Their thick peptidoglycan layer retains the crystal violet-iodine
complex
D) The safranin is more strongly attracted
16. The counterstain in the Gram stain procedure is:
A) Crystal violet
B) Iodine
C) Safranin
D) Methylene blue
17. A student over-decolorizes a Gram stain. What is the most likely
result?
A) Gram-positive cells will appear pink
B) Gram-negative cells will appear purple
C) All cells will appear colorless
D) The result will be unaffected
18. An acid-fast stain is used to identify bacteria in the genus:
A) Bacillus
B) Mycobacterium
C) Escherichia
D) Staphylococcus
WITH COMPLETE SOLUTIONS VERIFIED GRADED A++ LATEST
UPDATE 2025/2026
Microbiology Lab Final Exam: 100 Questions & Answers
1. What is the primary purpose of aseptic technique?
A) To make the lab work faster
B) To prevent contamination of cultures and the environment
C) To sterilize all equipment
D) To grow bacteria more efficiently
2. The lens of a microscope that is closest to the specimen is called
the:
A) Ocular lens
B) Objective lens
C) Condenser lens
D) Iris diaphragm
3. What is the total magnification when using the 100X oil immersion
objective with a standard 10X ocular lens?
A) 100X
B) 1000X
C) 400X
D) 2000X
4. Immersion oil is used with the 100X objective to:
A) Sterilize the lens
B) Increase the light refraction, improving resolution
C) Clean the slide
D) Decrease the magnification
,5. A medium whose exact chemical composition is known is called a:
A) Complex medium
B) Selective medium
C) Defined (Synthetic) medium
D) Differential medium
6. Mannitol Salt Agar (MSA) is both selective and differential. It is
selective for:
A) Gram-negative bacteria
B) Gram-positive bacteria, specifically Staphylococci
C) Lactose fermenters
D) Anaerobic bacteria
7. A bacterial colony that appears with a green, metallic sheen on
Eosin Methylene Blue (EMB) agar is indicative of:
A) Staphylococcus aureus
B) Pseudomonas aeruginosa
C) Escherichia coli
D) Proteus vulgaris
8. The process of killing all microorganisms, including bacterial
endospores, is called:
A) Disinfection
B) Antisepsis
C) Sanitization
D) Sterilization
9. Which of the following is the most resistant form of life?
A) Fungal spores
B) Protozoan cysts
,C) Bacterial endospores
D) Enveloped viruses
10. The standard autoclaving conditions for sterilization are:
A) 121°C at 15 psi for 15-20 minutes
B) 100°C for 10 minutes
C) 160°C for 2 hours
D) 71°C for 15 seconds
11. The method that provides a countable number of separate
colonies on an agar plate from a liquid culture is the:
A) Streak plate method
B) Pour plate method
C) Spread plate method
D) Broth dilution method
12. The purpose of the quadrant streak method is to:
A) Determine oxygen requirements
B) Observe colony pigmentation
C) Isolate pure cultures
D) Increase bacterial growth
13. A cloudy appearance in a liquid broth culture indicates:
A) Contamination
B) Bacterial growth
C) Sterility
D) A lack of nutrients
14. In a Gram stain, what is the function of the decolorizer (usually
alcohol/acetone)?
A) To fix the bacteria to the slide
, B) To stain Gram-negative cells
C) To remove the primary stain from Gram-negative cells
D) To stain Gram-positive cells
15. Gram-positive bacteria stain purple because:
A) They have a thin peptidoglycan layer
B) They have an outer membrane
C) Their thick peptidoglycan layer retains the crystal violet-iodine
complex
D) The safranin is more strongly attracted
16. The counterstain in the Gram stain procedure is:
A) Crystal violet
B) Iodine
C) Safranin
D) Methylene blue
17. A student over-decolorizes a Gram stain. What is the most likely
result?
A) Gram-positive cells will appear pink
B) Gram-negative cells will appear purple
C) All cells will appear colorless
D) The result will be unaffected
18. An acid-fast stain is used to identify bacteria in the genus:
A) Bacillus
B) Mycobacterium
C) Escherichia
D) Staphylococcus
