Page 1 of 122
BIOD171 (Latest ) Microbiology
Lab 1-9 Exams Portage Learning, 100 %
Guaranteed Pass ||Complete A+ Guide
1. Which objective lens requires oil immersion?
A) 4x
B) 10x
C) 40x
D) 100x
Answer: D) 100x
Rationale: The 100x objective has a very short working
distance; oil prevents light refraction, improving resolution.
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2. What is the total magnification when using a 10x ocular
and a 40x objective?
A) 40x
B) 100x
C) 400x
D) 4000x
Answer: C) 400x
Rationale: Total magnification = ocular × objective = 10 × 40
= 400x.
3. Which stain is used in the Gram stain to counterstain
Gramnegative bacteria?
A) Crystal violet
B) Iodine
C) Safranin
D) Methylene blue
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Answer: C) Safranin
Rationale: Safranin stains Gram-negative cells pink after
alcohol decolorization.
4. The purpose of heat-fixing a smear is to:
A) Stain the bacteria
B) Kill bacteria and adhere them to the slide
C) Enhance motility
D) Decolorize the cells
Answer: B) Kill bacteria and adhere them to the slide
Rationale: Heat fixation kills cells and fixes them to the slide
without distorting morphology.
5. Which of the following is a simple stain?
A) Gram stain
B) Acid-fast stain
, Page 4 of 122
C) Methylene blue
D) Endospore stain
Answer: C) Methylene blue
Rationale: Simple stains use a single dye to highlight cell
shape and arrangement.
True/False
6. (True/False) The resolving power of a microscope
improves as the wavelength of light increases.
Answer: False
Rationale: Shorter wavelengths give better resolution.
7. (True/False) Gram-positive bacteria retain crystal violet
after alcohol wash because of their thick peptidoglycan
layer.
Answer: True
BIOD171 (Latest ) Microbiology
Lab 1-9 Exams Portage Learning, 100 %
Guaranteed Pass ||Complete A+ Guide
1. Which objective lens requires oil immersion?
A) 4x
B) 10x
C) 40x
D) 100x
Answer: D) 100x
Rationale: The 100x objective has a very short working
distance; oil prevents light refraction, improving resolution.
,Page 2 of 122
2. What is the total magnification when using a 10x ocular
and a 40x objective?
A) 40x
B) 100x
C) 400x
D) 4000x
Answer: C) 400x
Rationale: Total magnification = ocular × objective = 10 × 40
= 400x.
3. Which stain is used in the Gram stain to counterstain
Gramnegative bacteria?
A) Crystal violet
B) Iodine
C) Safranin
D) Methylene blue
,Page 3 of 122
Answer: C) Safranin
Rationale: Safranin stains Gram-negative cells pink after
alcohol decolorization.
4. The purpose of heat-fixing a smear is to:
A) Stain the bacteria
B) Kill bacteria and adhere them to the slide
C) Enhance motility
D) Decolorize the cells
Answer: B) Kill bacteria and adhere them to the slide
Rationale: Heat fixation kills cells and fixes them to the slide
without distorting morphology.
5. Which of the following is a simple stain?
A) Gram stain
B) Acid-fast stain
, Page 4 of 122
C) Methylene blue
D) Endospore stain
Answer: C) Methylene blue
Rationale: Simple stains use a single dye to highlight cell
shape and arrangement.
True/False
6. (True/False) The resolving power of a microscope
improves as the wavelength of light increases.
Answer: False
Rationale: Shorter wavelengths give better resolution.
7. (True/False) Gram-positive bacteria retain crystal violet
after alcohol wash because of their thick peptidoglycan
layer.
Answer: True
