MICROBIOLOGY LAB · OBJECTIVE ASSESSMENT A+ VERIFIED
BIOD 171 Lab Exams 1–9 | Essential Microbiology |
Portage Learning | Actual Questions & Verified
Answers (2026/2027) — Complete
Official Exam
A+ Verified Questions Full Rationales Verified Answers
A+ 9 100%
QUESTIONS SECTIONS RATIONALES
Complete coverage One per lab exam Every answer explained
WHAT THIS COVERS
01 Lab 1 — Lab Safety, Notebook & Equipment
02 Lab 2 — Light Microscopy & Optics
03 Lab 3 — Gram Staining & Bacterial Morphology
04 Lab 4 — Growth Media & Culture Techniques
05 Lab 5 — Kirby-Bauer Antibiotic Sensitivity
06 Lab 6 — Enzymatic Assays (Oxidase, Catalase, Coagulase, Lipase)
07 Lab 7 — Secondary Assays (Indole, TSI, API)
08 Lab 8 — Antigen Detection (ELISA, Western Blot, Agglutination)
09 Lab 9 — Unknown Pathogen Identification
ABOUT THIS ASSESSMENT
Build mastery in essential microbiology laboratory skills — from aseptic technique, microscopy, and staining to microbial culture,
biochemical testing, and identification of unknown organisms across nine lab modules. This bank targets application and analysis skills
required for the Portage Learning BIOD 171 Lab Exams 1–9, with full rationales for every answer.
PASSING SCORE LEVEL FORMAT
80% Advanced (Upper-Division Biology — Lab) Application / Analysis
STUVIA ACTUAL EXAM Page 1
, SECTION 1: Lab 1 — Lab Safety, Notebook & Equipment
Q1. A student prepares to autoclave a stack of contaminated agar plates. The autoclave is set to 121 °C but the pressure
gauge reads only 10 psi. After the cycle finishes the student notices residual moisture and viable colonies on a control
plate. What is the most likely reason sterility was not achieved?
A. Temperature alone is sufficient; the pressure reading is irrelevant.
B. The combination of heat, pressure and steam was incomplete, preventing effective sterilization.
C. Agar plates cannot be sterilized in an autoclave under any conditions.
D. The cycle time was too long, causing over-heating and media degradation.
Correct Answer: B
Rationale: Autoclaves rely on the synergistic action of heat, pressure and saturated steam to achieve sterilization. At only 10 psi the required steam
penetration and temperature equivalence are not reached, allowing residual viable organisms.
Q2. While recording results in a lab notebook a student notices that a reagent concentration was changed after the first
three trials. According to standard notebook protocol, how should this deviation be documented?
A. Erase the original concentration and write the new value in black ink.
B. Write the new concentration in the margin without any special marking.
C. Omit the change because only final successful results are recorded.
D. Record the change in red ink so it is immediately visible and leave the original entry intact.
Correct Answer: D
Rationale: Deviations must be written in red to draw immediate attention while preserving the original entry. This maintains the legal and scientific
integrity of the permanent record.
Q3. A laboratory supervisor observes a student working at an open bench with a culture of Staphylococcus aureus while
wearing only a lab coat and no gloves. Which primary safety rule is being violated?
A. Lab coats are unnecessary when working with BSL-2 organisms.
B. Open benches are preferred for all bacterial work to allow better airflow.
C. Gloves are required personal protective equipment when handling live bacterial cultures.
D. Only thermal gloves are needed when handling cultures.
Correct Answer: C
Rationale: Direct contact with live cultures requires gloves as part of standard PPE. Lab coats alone do not protect the hands from potential
contamination or infection.
Q4. An autoclave cycle reaches 121 °C and 15 psi for 15 minutes, yet a biological indicator still shows growth. The most
probable cause is:
A. The autoclave temperature was set too high.
B. The pressure was excessive and killed the indicator organisms too quickly.
C. Biological indicators are never reliable for verifying sterilization.
D. The indicator was placed outside the load and never exposed to steam.
Correct Answer: D
Rationale: Biological indicators must be placed within the densest part of the load to confirm steam penetration. Placement outside the load yields a
false-negative result for sterilization success.
STUVIA ACTUAL EXAM Page 2
, SECTION 1: Lab 1 — Lab Safety, Notebook & Equipment
Q5. A student needs to cool a freshly autoclaved bottle of liquid media before pouring plates. Which piece of equipment is
most appropriate for rapid, controlled cooling without contamination risk?
A. An open water bath on the bench top.
B. A laminar-flow hood with a sterile cooling rack.
C. A household refrigerator with the door left ajar.
D. A microwave oven set on low power.
Correct Answer: B
Rationale: A laminar-flow hood provides a sterile air stream that protects the open media while it cools, minimizing airborne contamination risk that
would occur on an open bench.
Q6. During a safety briefing the instructor emphasizes three rules that protect both the worker and others from
contamination. Which set correctly lists those rules?
A. Never eat in the lab, always wear open-toed shoes, and leave cultures on the open bench overnight.
B. Wear appropriate PPE, decontaminate work surfaces before and after use, and never mouth-pipette.
C. Only sterilize glassware, ignore spills, and store cultures at room temperature.
D. Use only latex gloves, work without a lab coat, and dispose of sharps in regular trash.
Correct Answer: B
Rationale: Standard laboratory safety requires PPE, surface decontamination, and prohibition of mouth-pipetting to prevent both personal exposure
and laboratory-acquired infections.
Q7. A fixed incubator is set at 37 °C. Why is this temperature chosen for most clinical bacterial cultures?
A. It is the only temperature at which agar remains solid.
B. It kills all non-pathogenic contaminants automatically.
C. It prevents any oxygen from entering the chamber.
D. It matches the average human body temperature, allowing optimal growth of human pathogens.
Correct Answer: D
Rationale: Human pathogens have evolved to grow optimally near 37 °C. Incubation at this temperature therefore selects for organisms relevant to
clinical specimens.
Q8. A student must transfer a pure culture from a slant to a sterile broth tube. After flaming the inoculating loop, the
student immediately inserts the hot loop into the culture. What is the consequence?
A. The loop is sterilized more thoroughly, improving the transfer.
B. The culture is killed by residual heat, and the transfer fails.
C. No effect occurs because the culture is heat-resistant.
D. The broth becomes over-inoculated and turbid within minutes.
Correct Answer: B
Rationale: A hot loop will kill the organisms it contacts. The loop must be allowed to cool for several seconds before touching the living culture.
Q9. Which of the following glove types is specifically designed to protect against extreme cold when handling frozen stock
cultures?
A. Nitrile examination gloves
B. Latex surgical gloves
C. Thermal cold-protective gloves
D. Standard vinyl gloves
Correct Answer: C
Rationale: Thermal cold gloves are engineered for cryogenic or freezer temperatures and prevent frostbite when retrieving frozen bacterial stocks.
STUVIA ACTUAL EXAM Page 3
, SECTION 1: Lab 1 — Lab Safety, Notebook & Equipment
Q10. A lab notebook entry must include the date, a clear objective, materials, procedure, results, and conclusions. A
student omits the results section and writes only a final conclusion. Why is this incomplete?
A. Conclusions alone are sufficient for grading.
B. Without recorded observations the conclusion cannot be independently verified or reproduced.
C. Results are optional when the experiment succeeds.
D. Only the procedure section is required by accreditation standards.
Correct Answer: B
Rationale: Scientific notebooks serve as permanent, verifiable records. Raw results must be present so that any later reader can evaluate the validity
of the stated conclusion.
Q11. An autoclave tape indicator turns black after a cycle, yet a spore strip still grows. The most accurate interpretation is:
A. Chemical indicators confirm exposure to heat but do not guarantee sterilization; biological indicators are definitive.
B. The tape proves sterilization; the spore strip must be defective.
C. Both indicators are unreliable and should be ignored.
D. The autoclave reached sterilizing temperature but the tape failed.
Correct Answer: A
Rationale: Chemical indicators (tape) change color with heat exposure only. Biological indicators containing resistant spores provide the only direct
proof of sterilization.
Q12. A student is about to dispose of a culture of E. coli that has been growing in liquid LB. The correct disposal method
is:
A. Pour the culture down the laboratory sink with running water.
B. Autoclave the culture before discarding it as biohazard waste.
C. Place the open tube in the regular trash after capping it.
D. Neutralize the culture with household bleach and then pour it outside.
Correct Answer: B
Rationale: All live bacterial cultures must be sterilized by autoclaving before disposal to eliminate any residual infectious risk.
Q13. When labeling a sterile agar plate that will be incubated inverted, where should the label be written and why?
A. On the lid so it is easily readable without opening the plate.
B. On the bottom (agar side) so the label remains with the culture if the lid is misplaced.
C. On both lid and bottom in different colors for cross-checking.
D. Labels are unnecessary if the plate is placed in a numbered rack.
Correct Answer: B
Rationale: Writing on the bottom ensures the identifying information stays with the agar even if lids are swapped or lost during handling.
Q14. A laminar-flow hood is running but the UV light is left on while a student works inside the cabinet. What is the
primary hazard?
A. UV light will sterilize the student’s gloves and is therefore beneficial.
B. UV light has no effect on living tissue at the wavelengths used.
C. The only risk is that the UV bulb will burn out prematurely.
D. Direct UV exposure can cause skin and eye damage to the operator.
Correct Answer: D
Rationale: Germicidal UV lamps emit wavelengths that damage human DNA and corneal tissue. The light must be turned off before any operator
works inside the cabinet.
STUVIA ACTUAL EXAM Page 4
BIOD 171 Lab Exams 1–9 | Essential Microbiology |
Portage Learning | Actual Questions & Verified
Answers (2026/2027) — Complete
Official Exam
A+ Verified Questions Full Rationales Verified Answers
A+ 9 100%
QUESTIONS SECTIONS RATIONALES
Complete coverage One per lab exam Every answer explained
WHAT THIS COVERS
01 Lab 1 — Lab Safety, Notebook & Equipment
02 Lab 2 — Light Microscopy & Optics
03 Lab 3 — Gram Staining & Bacterial Morphology
04 Lab 4 — Growth Media & Culture Techniques
05 Lab 5 — Kirby-Bauer Antibiotic Sensitivity
06 Lab 6 — Enzymatic Assays (Oxidase, Catalase, Coagulase, Lipase)
07 Lab 7 — Secondary Assays (Indole, TSI, API)
08 Lab 8 — Antigen Detection (ELISA, Western Blot, Agglutination)
09 Lab 9 — Unknown Pathogen Identification
ABOUT THIS ASSESSMENT
Build mastery in essential microbiology laboratory skills — from aseptic technique, microscopy, and staining to microbial culture,
biochemical testing, and identification of unknown organisms across nine lab modules. This bank targets application and analysis skills
required for the Portage Learning BIOD 171 Lab Exams 1–9, with full rationales for every answer.
PASSING SCORE LEVEL FORMAT
80% Advanced (Upper-Division Biology — Lab) Application / Analysis
STUVIA ACTUAL EXAM Page 1
, SECTION 1: Lab 1 — Lab Safety, Notebook & Equipment
Q1. A student prepares to autoclave a stack of contaminated agar plates. The autoclave is set to 121 °C but the pressure
gauge reads only 10 psi. After the cycle finishes the student notices residual moisture and viable colonies on a control
plate. What is the most likely reason sterility was not achieved?
A. Temperature alone is sufficient; the pressure reading is irrelevant.
B. The combination of heat, pressure and steam was incomplete, preventing effective sterilization.
C. Agar plates cannot be sterilized in an autoclave under any conditions.
D. The cycle time was too long, causing over-heating and media degradation.
Correct Answer: B
Rationale: Autoclaves rely on the synergistic action of heat, pressure and saturated steam to achieve sterilization. At only 10 psi the required steam
penetration and temperature equivalence are not reached, allowing residual viable organisms.
Q2. While recording results in a lab notebook a student notices that a reagent concentration was changed after the first
three trials. According to standard notebook protocol, how should this deviation be documented?
A. Erase the original concentration and write the new value in black ink.
B. Write the new concentration in the margin without any special marking.
C. Omit the change because only final successful results are recorded.
D. Record the change in red ink so it is immediately visible and leave the original entry intact.
Correct Answer: D
Rationale: Deviations must be written in red to draw immediate attention while preserving the original entry. This maintains the legal and scientific
integrity of the permanent record.
Q3. A laboratory supervisor observes a student working at an open bench with a culture of Staphylococcus aureus while
wearing only a lab coat and no gloves. Which primary safety rule is being violated?
A. Lab coats are unnecessary when working with BSL-2 organisms.
B. Open benches are preferred for all bacterial work to allow better airflow.
C. Gloves are required personal protective equipment when handling live bacterial cultures.
D. Only thermal gloves are needed when handling cultures.
Correct Answer: C
Rationale: Direct contact with live cultures requires gloves as part of standard PPE. Lab coats alone do not protect the hands from potential
contamination or infection.
Q4. An autoclave cycle reaches 121 °C and 15 psi for 15 minutes, yet a biological indicator still shows growth. The most
probable cause is:
A. The autoclave temperature was set too high.
B. The pressure was excessive and killed the indicator organisms too quickly.
C. Biological indicators are never reliable for verifying sterilization.
D. The indicator was placed outside the load and never exposed to steam.
Correct Answer: D
Rationale: Biological indicators must be placed within the densest part of the load to confirm steam penetration. Placement outside the load yields a
false-negative result for sterilization success.
STUVIA ACTUAL EXAM Page 2
, SECTION 1: Lab 1 — Lab Safety, Notebook & Equipment
Q5. A student needs to cool a freshly autoclaved bottle of liquid media before pouring plates. Which piece of equipment is
most appropriate for rapid, controlled cooling without contamination risk?
A. An open water bath on the bench top.
B. A laminar-flow hood with a sterile cooling rack.
C. A household refrigerator with the door left ajar.
D. A microwave oven set on low power.
Correct Answer: B
Rationale: A laminar-flow hood provides a sterile air stream that protects the open media while it cools, minimizing airborne contamination risk that
would occur on an open bench.
Q6. During a safety briefing the instructor emphasizes three rules that protect both the worker and others from
contamination. Which set correctly lists those rules?
A. Never eat in the lab, always wear open-toed shoes, and leave cultures on the open bench overnight.
B. Wear appropriate PPE, decontaminate work surfaces before and after use, and never mouth-pipette.
C. Only sterilize glassware, ignore spills, and store cultures at room temperature.
D. Use only latex gloves, work without a lab coat, and dispose of sharps in regular trash.
Correct Answer: B
Rationale: Standard laboratory safety requires PPE, surface decontamination, and prohibition of mouth-pipetting to prevent both personal exposure
and laboratory-acquired infections.
Q7. A fixed incubator is set at 37 °C. Why is this temperature chosen for most clinical bacterial cultures?
A. It is the only temperature at which agar remains solid.
B. It kills all non-pathogenic contaminants automatically.
C. It prevents any oxygen from entering the chamber.
D. It matches the average human body temperature, allowing optimal growth of human pathogens.
Correct Answer: D
Rationale: Human pathogens have evolved to grow optimally near 37 °C. Incubation at this temperature therefore selects for organisms relevant to
clinical specimens.
Q8. A student must transfer a pure culture from a slant to a sterile broth tube. After flaming the inoculating loop, the
student immediately inserts the hot loop into the culture. What is the consequence?
A. The loop is sterilized more thoroughly, improving the transfer.
B. The culture is killed by residual heat, and the transfer fails.
C. No effect occurs because the culture is heat-resistant.
D. The broth becomes over-inoculated and turbid within minutes.
Correct Answer: B
Rationale: A hot loop will kill the organisms it contacts. The loop must be allowed to cool for several seconds before touching the living culture.
Q9. Which of the following glove types is specifically designed to protect against extreme cold when handling frozen stock
cultures?
A. Nitrile examination gloves
B. Latex surgical gloves
C. Thermal cold-protective gloves
D. Standard vinyl gloves
Correct Answer: C
Rationale: Thermal cold gloves are engineered for cryogenic or freezer temperatures and prevent frostbite when retrieving frozen bacterial stocks.
STUVIA ACTUAL EXAM Page 3
, SECTION 1: Lab 1 — Lab Safety, Notebook & Equipment
Q10. A lab notebook entry must include the date, a clear objective, materials, procedure, results, and conclusions. A
student omits the results section and writes only a final conclusion. Why is this incomplete?
A. Conclusions alone are sufficient for grading.
B. Without recorded observations the conclusion cannot be independently verified or reproduced.
C. Results are optional when the experiment succeeds.
D. Only the procedure section is required by accreditation standards.
Correct Answer: B
Rationale: Scientific notebooks serve as permanent, verifiable records. Raw results must be present so that any later reader can evaluate the validity
of the stated conclusion.
Q11. An autoclave tape indicator turns black after a cycle, yet a spore strip still grows. The most accurate interpretation is:
A. Chemical indicators confirm exposure to heat but do not guarantee sterilization; biological indicators are definitive.
B. The tape proves sterilization; the spore strip must be defective.
C. Both indicators are unreliable and should be ignored.
D. The autoclave reached sterilizing temperature but the tape failed.
Correct Answer: A
Rationale: Chemical indicators (tape) change color with heat exposure only. Biological indicators containing resistant spores provide the only direct
proof of sterilization.
Q12. A student is about to dispose of a culture of E. coli that has been growing in liquid LB. The correct disposal method
is:
A. Pour the culture down the laboratory sink with running water.
B. Autoclave the culture before discarding it as biohazard waste.
C. Place the open tube in the regular trash after capping it.
D. Neutralize the culture with household bleach and then pour it outside.
Correct Answer: B
Rationale: All live bacterial cultures must be sterilized by autoclaving before disposal to eliminate any residual infectious risk.
Q13. When labeling a sterile agar plate that will be incubated inverted, where should the label be written and why?
A. On the lid so it is easily readable without opening the plate.
B. On the bottom (agar side) so the label remains with the culture if the lid is misplaced.
C. On both lid and bottom in different colors for cross-checking.
D. Labels are unnecessary if the plate is placed in a numbered rack.
Correct Answer: B
Rationale: Writing on the bottom ensures the identifying information stays with the agar even if lids are swapped or lost during handling.
Q14. A laminar-flow hood is running but the UV light is left on while a student works inside the cabinet. What is the
primary hazard?
A. UV light will sterilize the student’s gloves and is therefore beneficial.
B. UV light has no effect on living tissue at the wavelengths used.
C. The only risk is that the UV bulb will burn out prematurely.
D. Direct UV exposure can cause skin and eye damage to the operator.
Correct Answer: D
Rationale: Germicidal UV lamps emit wavelengths that damage human DNA and corneal tissue. The light must be turned off before any operator
works inside the cabinet.
STUVIA ACTUAL EXAM Page 4
