,Sample General Microbiology Lab 2 Practice Questions & Topics
Format: Each question uses a ✓ to mark the correct answer.
Section 1: Aseptic Technique & Culturing
1. The primary goal of aseptic technique is to:
a) Speed up the growth of bacteria
b) Prevent contamination of pure cultures and the environment ✓
c) Make media plates easier to pour
d) Sterilize all tools using soap and water
2. When performing a quadrant streak for isolation, the inoculating loop is sterilized:
a) Only at the beginning of the procedure
b) After streaking each of the four quadrants ✓
c) Only if you touch the bench
d) It does not need to be re-sterilized during the procedure
3. A pure culture is best defined as:
a) A culture containing multiple species of microbes
b) A culture containing a single species of microbe ✓
c) A culture grown on general purpose media
d) A culture that appears cloudy in a broth tube
Section 2: Staining Techniques
4. The primary stain used in the Gram stain procedure is:
a) Safranin
b) Iodine (mordant)
c) Crystal Violet ✓
d) Ethanol (decolorizer)
5. In a properly executed Gram stain, Gram-positive bacteria will appear:
a) Pink/Red
b) Purple/Violet ✓
c) Colorless
d) Green
6. The critical step that differentiates Gram-positive from Gram-negative cells is the:
a) Application of the mordant
, b) Application of the primary stain
c) Decolorization step ✓
d) Application of the counterstain
7. Acid-fast stains (like Ziehl-Neelsen) are used primarily to identify bacteria with:
a) Thick peptidoglycan layers
b) Waxy mycolic acid in their cell walls ✓
c) Large capsules
d) Numerous flagella
Section 3: Microscopy
8. The objective lens that provides the highest total magnification on a standard compound
light microscope is:
a) 4x (scanning)
b) 10x (low power)
c) 40x (high dry)
d) 100x (oil immersion) ✓
9. Immersion oil is used with the 100x objective to:
a) Clean the lens
b) Increase the light refraction, improving resolution ✓
c) Slow down fast-moving bacteria
d) Sterilize the slide
10. Parfocal means:
a) The microscope has two ocular lenses
b) The specimen remains in approximate focus when switching between objective lenses
✓
c) The microscope uses a single focus knob
d) The stage can be moved horizontally
Section 4: Metabolic & Biochemical Tests
11. A catalase test is performed by adding hydrogen peroxide to a bacterial sample. The
production of bubbles indicates:
a) The presence of the enzyme cytochrome oxidase
b) The fermentation of lactose
c) The breakdown of hydrogen peroxide into water and oxygen gas ✓
d) The production of mixed acids
, 12. In a SIM deep, bacterial motility is evidenced by:
a) A black precipitate along the stab line
b) A red color change after adding reagents
c) Cloudiness throughout the tube
d) Growth radiating outward from the central stab line ✓
13. A bacterium that can ferment lactose in MacConkey Agar will typically produce:
a) Colorless colonies and no change in the medium
b) Pink/red colonies and a pink halo in the medium ✓
c) A blue-green pigment
d) A black precipitate
Section 5: Media Types & Purpose
14. Mannitol Salt Agar (MSA) is both selective and differential. It is selective for:
a) Gram-negative bacteria
b) Bacteria that ferment mannitol
c) Bacteria that can tolerate high salt concentrations (halophiles) ✓
d) Bacteria that produce hydrogen sulfide
15. Blood Agar is used primarily to observe:
a) Lactose fermentation
b) Hemolytic patterns (alpha, beta, gamma) ✓
c) Indole production
d) Motility
How to Use This for Effective Study:
1. Review Your Lab Manual & Notes: This is your primary resource. The actual exam will be
derived directly from your specific lab exercises and objectives.
2. Focus on "Why": Don't just memorize answers. Understand why Gram-positive cells
retain the stain, why we use immersion oil, why a medium is selective.
3. Make Your Own Flashcards: Create cards for key terms, stain steps, media components,
and test interpretations.
4. Redraw Procedures: From memory, draw the steps of the Gram stain or the pattern of a
quadrant streak.
Format: Each question uses a ✓ to mark the correct answer.
Section 1: Aseptic Technique & Culturing
1. The primary goal of aseptic technique is to:
a) Speed up the growth of bacteria
b) Prevent contamination of pure cultures and the environment ✓
c) Make media plates easier to pour
d) Sterilize all tools using soap and water
2. When performing a quadrant streak for isolation, the inoculating loop is sterilized:
a) Only at the beginning of the procedure
b) After streaking each of the four quadrants ✓
c) Only if you touch the bench
d) It does not need to be re-sterilized during the procedure
3. A pure culture is best defined as:
a) A culture containing multiple species of microbes
b) A culture containing a single species of microbe ✓
c) A culture grown on general purpose media
d) A culture that appears cloudy in a broth tube
Section 2: Staining Techniques
4. The primary stain used in the Gram stain procedure is:
a) Safranin
b) Iodine (mordant)
c) Crystal Violet ✓
d) Ethanol (decolorizer)
5. In a properly executed Gram stain, Gram-positive bacteria will appear:
a) Pink/Red
b) Purple/Violet ✓
c) Colorless
d) Green
6. The critical step that differentiates Gram-positive from Gram-negative cells is the:
a) Application of the mordant
, b) Application of the primary stain
c) Decolorization step ✓
d) Application of the counterstain
7. Acid-fast stains (like Ziehl-Neelsen) are used primarily to identify bacteria with:
a) Thick peptidoglycan layers
b) Waxy mycolic acid in their cell walls ✓
c) Large capsules
d) Numerous flagella
Section 3: Microscopy
8. The objective lens that provides the highest total magnification on a standard compound
light microscope is:
a) 4x (scanning)
b) 10x (low power)
c) 40x (high dry)
d) 100x (oil immersion) ✓
9. Immersion oil is used with the 100x objective to:
a) Clean the lens
b) Increase the light refraction, improving resolution ✓
c) Slow down fast-moving bacteria
d) Sterilize the slide
10. Parfocal means:
a) The microscope has two ocular lenses
b) The specimen remains in approximate focus when switching between objective lenses
✓
c) The microscope uses a single focus knob
d) The stage can be moved horizontally
Section 4: Metabolic & Biochemical Tests
11. A catalase test is performed by adding hydrogen peroxide to a bacterial sample. The
production of bubbles indicates:
a) The presence of the enzyme cytochrome oxidase
b) The fermentation of lactose
c) The breakdown of hydrogen peroxide into water and oxygen gas ✓
d) The production of mixed acids
, 12. In a SIM deep, bacterial motility is evidenced by:
a) A black precipitate along the stab line
b) A red color change after adding reagents
c) Cloudiness throughout the tube
d) Growth radiating outward from the central stab line ✓
13. A bacterium that can ferment lactose in MacConkey Agar will typically produce:
a) Colorless colonies and no change in the medium
b) Pink/red colonies and a pink halo in the medium ✓
c) A blue-green pigment
d) A black precipitate
Section 5: Media Types & Purpose
14. Mannitol Salt Agar (MSA) is both selective and differential. It is selective for:
a) Gram-negative bacteria
b) Bacteria that ferment mannitol
c) Bacteria that can tolerate high salt concentrations (halophiles) ✓
d) Bacteria that produce hydrogen sulfide
15. Blood Agar is used primarily to observe:
a) Lactose fermentation
b) Hemolytic patterns (alpha, beta, gamma) ✓
c) Indole production
d) Motility
How to Use This for Effective Study:
1. Review Your Lab Manual & Notes: This is your primary resource. The actual exam will be
derived directly from your specific lab exercises and objectives.
2. Focus on "Why": Don't just memorize answers. Understand why Gram-positive cells
retain the stain, why we use immersion oil, why a medium is selective.
3. Make Your Own Flashcards: Create cards for key terms, stain steps, media components,
and test interpretations.
4. Redraw Procedures: From memory, draw the steps of the Gram stain or the pattern of a
quadrant streak.
