BIO 171 M5 Module 5 Review Essential
Microbiology Lab Exam Actual 2026/2027 –
Complete 40-Question Review with Detailed
Rationales | 100% Verified | Pass Guaranteed –
A+ Graded
Section A: Microbial Ecology & Environmental Microbiology
Q1: A Pseudomonas aeruginosa contamination is identified on the surface of a hospital
catheter. Microscopic examination reveals the bacteria encased in a self-produced
matrix of polysaccharides, proteins, and extracellular DNA adhered to the device
surface. This structured microbial community is BEST described as:
A. A planktonic population in logarithmic growth
B. A biofilm [CORRECT]
C. A mutualistic lichen symbiosis
D. A transient microbiota colonization
Correct Answer: B
Rationale: A biofilm is a surface-attached microbial community encased in an
extracellular polymeric substance (EPS) matrix that provides protection, facilitates
nutrient exchange, and increases resistance to antimicrobials. Planktonic bacteria are
free-floating, lichens are fungal-algal mutualisms, and transient microbiota do not form
structured matrices.
,Q2: Root nodules of leguminous plants contain nitrogen-fixing bacteria that convert
atmospheric N₂ into ammonia, providing usable nitrogen to the plant while receiving
carbohydrates and shelter from the plant. This relationship is classified as:
A. Commensalism
B. Mutualism [CORRECT]
C. Parasitism
D. Competition
Correct Answer: B
Rationale: Mutualism is a symbiotic relationship in which both organisms benefit. The
bacterium (Rhizobium or Bradyrhizobium) receives nutrients and protection, while the
plant receives biologically available nitrogen. Commensalism benefits only one
organism, parasism harms the host, and competition is antagonistic.
Q3: In a municipal wastewater treatment facility, aerobic bacteria are used to degrade
organic matter in large aeration tanks. This biological treatment stage is known as:
A. Primary treatment (sedimentation)
B. Secondary treatment (activated sludge process) [CORRECT]
C. Tertiary treatment (nutrient removal)
D. Anaerobic digestion
Correct Answer: B
, Rationale: Secondary treatment utilizes microbial metabolism in the activated sludge
process to aerobically degrade dissolved and suspended organic material. Primary
treatment removes solids physically, tertiary treatment removes nutrients, and
anaerobic digestion occurs without oxygen.
Q4: A water quality technician tests a river sample for fecal contamination using the
most probable number (MPN) method with lactose broth tubes. Gas production in the
tubes indicates the presence of:
A. Cyanobacteria
B. Coliforms [CORRECT]
C. Sulfur-oxidizing bacteria
D. Denitrifying bacteria
Correct Answer: B
Rationale: The MPN method detects coliforms (indicator organisms of fecal
contamination) by their ability to ferment lactose, producing gas and acid.
Cyanobacteria, sulfur-oxidizers, and denitrifiers do not produce gas from lactose
fermentation.
Q5: Fungal hyphae form symbiotic associations with plant roots, increasing the surface
area for water and mineral absorption while receiving photosynthetic products from the
plant. This association is known as:
A. Lichenization
B. Mycorrhizae [CORRECT]
Microbiology Lab Exam Actual 2026/2027 –
Complete 40-Question Review with Detailed
Rationales | 100% Verified | Pass Guaranteed –
A+ Graded
Section A: Microbial Ecology & Environmental Microbiology
Q1: A Pseudomonas aeruginosa contamination is identified on the surface of a hospital
catheter. Microscopic examination reveals the bacteria encased in a self-produced
matrix of polysaccharides, proteins, and extracellular DNA adhered to the device
surface. This structured microbial community is BEST described as:
A. A planktonic population in logarithmic growth
B. A biofilm [CORRECT]
C. A mutualistic lichen symbiosis
D. A transient microbiota colonization
Correct Answer: B
Rationale: A biofilm is a surface-attached microbial community encased in an
extracellular polymeric substance (EPS) matrix that provides protection, facilitates
nutrient exchange, and increases resistance to antimicrobials. Planktonic bacteria are
free-floating, lichens are fungal-algal mutualisms, and transient microbiota do not form
structured matrices.
,Q2: Root nodules of leguminous plants contain nitrogen-fixing bacteria that convert
atmospheric N₂ into ammonia, providing usable nitrogen to the plant while receiving
carbohydrates and shelter from the plant. This relationship is classified as:
A. Commensalism
B. Mutualism [CORRECT]
C. Parasitism
D. Competition
Correct Answer: B
Rationale: Mutualism is a symbiotic relationship in which both organisms benefit. The
bacterium (Rhizobium or Bradyrhizobium) receives nutrients and protection, while the
plant receives biologically available nitrogen. Commensalism benefits only one
organism, parasism harms the host, and competition is antagonistic.
Q3: In a municipal wastewater treatment facility, aerobic bacteria are used to degrade
organic matter in large aeration tanks. This biological treatment stage is known as:
A. Primary treatment (sedimentation)
B. Secondary treatment (activated sludge process) [CORRECT]
C. Tertiary treatment (nutrient removal)
D. Anaerobic digestion
Correct Answer: B
, Rationale: Secondary treatment utilizes microbial metabolism in the activated sludge
process to aerobically degrade dissolved and suspended organic material. Primary
treatment removes solids physically, tertiary treatment removes nutrients, and
anaerobic digestion occurs without oxygen.
Q4: A water quality technician tests a river sample for fecal contamination using the
most probable number (MPN) method with lactose broth tubes. Gas production in the
tubes indicates the presence of:
A. Cyanobacteria
B. Coliforms [CORRECT]
C. Sulfur-oxidizing bacteria
D. Denitrifying bacteria
Correct Answer: B
Rationale: The MPN method detects coliforms (indicator organisms of fecal
contamination) by their ability to ferment lactose, producing gas and acid.
Cyanobacteria, sulfur-oxidizers, and denitrifiers do not produce gas from lactose
fermentation.
Q5: Fungal hyphae form symbiotic associations with plant roots, increasing the surface
area for water and mineral absorption while receiving photosynthetic products from the
plant. This association is known as:
A. Lichenization
B. Mycorrhizae [CORRECT]
