A+ VERIFIED
MICROBIOLOGY · OBJECTIVE ASSESSMENT
BIOD 171 Essential Microbiology – Modules 1–6 Exam
& Final Exam (2026/2027) Portage learning/Geneva College — Complete
Official Exam
A+ Verified Questions Full Rationales Verified Answers
A+ 5 100%
QUESTIONS SECTIONS RATIONALES
Complete coverage Core exam domains Every answer explained
WHAT THIS COVERS
01 Microbial Cell Structure, Microscopy & Classification
02 Microbial Growth, Metabolism & Nutrition
03 Microbial Genetics & Molecular Biology
04 Control of Microbial Growth & Antimicrobials
05 Host Defenses, Pathogenesis & Selected Pathogens
ABOUT THIS ASSESSMENT
Build mastery in essential microbiology — from microbial cell structure
and classification to microbial growth, metabolism, genetics, control
methods, host-pathogen interactions, and the immune response. This
assessment targets application and analysis skills required for the
Portage Learning BIOD 171 Modules 1–6 and Final Exam, with full rationales.
PASSING SCORE LEVEL FORMAT
80% Advanced (Upper-Division Biology) Application / Analysis
STUVIA ACTUAL EXAM Page 1
, SECTION 1: Microbial Cell Structure, Microscopy & Classification
Q1. A technician examines a bacterial smear and notes retention of crystal violet after decolorization. The organism most likely possesses:
A. A thick peptidoglycan layer typical of Gram-positive cells
B. A thin peptidoglycan layer and an outer membrane
C. Mycolic acids requiring acid-fast staining
D. No cell wall at all
Correct Answer: A
Rationale:
Gram-positive bacteria retain crystal violet because of their thick peptidoglycan. Gram-negative organisms decolorize; acid-fast and cell-wall-deficient organisms require
different staining approaches.
Q2. Increasing the numerical aperture of a microscope objective primarily improves:
A. Magnification of the ocular only
B. Resolving power (resolution) of the system
C. Contrast without changing resolution
D. Working distance from the slide
Correct Answer: B
Rationale:
Resolution depends on wavelength and numerical aperture. Higher NA improves the ability to distinguish closely spaced points.
Q3. A bacterial capsule that inhibits phagocytosis is composed primarily of:
A. Polysaccharide or polypeptide external to the cell wall
B. Peptidoglycan cross-links
C. Lipopolysaccharide unique to Gram-negatives
D. Mycolic acids of the acid-fast envelope
Correct Answer: A
Rationale:
Capsules are typically polysaccharide (or polypeptide) layers outside the wall that impede phagocytosis.
Q4. An organism lacks a nucleus and membrane-bound organelles but has 70S ribosomes and a circular chromosome. It belongs to:
A. Eukarya
B. Viruses
C. Bacteria or Archaea
D. Fungi
Correct Answer: C
Rationale:
Prokaryotes (Bacteria and Archaea) lack nuclei and membrane-bound organelles and possess 70S ribosomes and circular chromosomes.
Q5. In an endospore stain, green structures inside pink vegetative cells represent:
A. Endospores that are highly resistant to stress
B. Capsules
C. Flagella
D. Nucleoids
Correct Answer: A
Rationale:
Malachite green stains endospores; safranin counterstains vegetative cells pink/red.
Q6. Pili that mediate attachment to host cells are composed of:
A. Flagellin
B. Peptidoglycan subunits
C. Pilin protein subunits
D. Lipid A
Correct Answer: C
Rationale:
Pili (fimbriae) are built from pilin subunits and function mainly in adhesion.
STUVIA ACTUAL EXAM · Page 2
, SECTION 1: Microbial Cell Structure, Microscopy & Classification
Q7. A bacterial cell placed in a hypertonic solution undergoes plasmolysis because:
A. Water leaves and the cytoplasm shrinks from the wall
B. Water enters and the cell lyses
C. The wall dissolves completely
D. Active transport pumps solutes inward
Correct Answer: A
Rationale:
Hypertonic conditions cause water efflux and plasmolysis.
Q8. EDTA is required with lysozyme to produce spheroplasts from Gram-negative cells because it:
A. Destabilizes the outer membrane so lysozyme can reach peptidoglycan
B. Digests thick peptidoglycan
C. Inhibits 70S ribosomes
D. Cross-links peptide side chains
Correct Answer: A
Rationale:
EDTA chelates cations that stabilize the outer membrane, allowing lysozyme access.
Q9. The difference between bacterial 70S and eukaryotic 80S ribosomes is clinically important because it:
A. Makes all antibiotics equally toxic to host cells
B. Means bacteria lack ribosomes
C. Means eukaryotic cells have no protein synthesis
D. Allows selective antibiotic toxicity against bacterial protein synthesis
Correct Answer: D
Rationale:
Structural differences between 70S and 80S ribosomes permit selective inhibition by many antibiotics.
Q10. Acid-fast organisms resist acid-alcohol decolorization because of:
A. Thick peptidoglycan alone
B. Mycolic acids that create a waxy impermeable barrier
C. An outer membrane of LPS
D. Absence of any cell wall
Correct Answer: B
Rationale:
Mycolic acids confer the acid-fast property.
Q11. Corkscrew motility of spirochetes is produced by:
A. Peritrichous flagella
B. Pili that twitch
C. Eukaryotic-style cilia
D. Axial filaments (endoflagella) in the periplasm
Correct Answer: D
Rationale:
Spirochetes use periplasmic axial filaments for characteristic motility.
Q12. Isolation of pure colonies on solid medium is achieved by the:
A. Broth dilution method
B. Streak-plate method that progressively dilutes the inoculum
C. Direct microscopic count
D. Turbidimetric OD measurement
Correct Answer: B
Rationale:
Streak plating spatially dilutes cells so individual colonies arise from single CFUs.
STUVIA ACTUAL EXAM · Page 3
MICROBIOLOGY · OBJECTIVE ASSESSMENT
BIOD 171 Essential Microbiology – Modules 1–6 Exam
& Final Exam (2026/2027) Portage learning/Geneva College — Complete
Official Exam
A+ Verified Questions Full Rationales Verified Answers
A+ 5 100%
QUESTIONS SECTIONS RATIONALES
Complete coverage Core exam domains Every answer explained
WHAT THIS COVERS
01 Microbial Cell Structure, Microscopy & Classification
02 Microbial Growth, Metabolism & Nutrition
03 Microbial Genetics & Molecular Biology
04 Control of Microbial Growth & Antimicrobials
05 Host Defenses, Pathogenesis & Selected Pathogens
ABOUT THIS ASSESSMENT
Build mastery in essential microbiology — from microbial cell structure
and classification to microbial growth, metabolism, genetics, control
methods, host-pathogen interactions, and the immune response. This
assessment targets application and analysis skills required for the
Portage Learning BIOD 171 Modules 1–6 and Final Exam, with full rationales.
PASSING SCORE LEVEL FORMAT
80% Advanced (Upper-Division Biology) Application / Analysis
STUVIA ACTUAL EXAM Page 1
, SECTION 1: Microbial Cell Structure, Microscopy & Classification
Q1. A technician examines a bacterial smear and notes retention of crystal violet after decolorization. The organism most likely possesses:
A. A thick peptidoglycan layer typical of Gram-positive cells
B. A thin peptidoglycan layer and an outer membrane
C. Mycolic acids requiring acid-fast staining
D. No cell wall at all
Correct Answer: A
Rationale:
Gram-positive bacteria retain crystal violet because of their thick peptidoglycan. Gram-negative organisms decolorize; acid-fast and cell-wall-deficient organisms require
different staining approaches.
Q2. Increasing the numerical aperture of a microscope objective primarily improves:
A. Magnification of the ocular only
B. Resolving power (resolution) of the system
C. Contrast without changing resolution
D. Working distance from the slide
Correct Answer: B
Rationale:
Resolution depends on wavelength and numerical aperture. Higher NA improves the ability to distinguish closely spaced points.
Q3. A bacterial capsule that inhibits phagocytosis is composed primarily of:
A. Polysaccharide or polypeptide external to the cell wall
B. Peptidoglycan cross-links
C. Lipopolysaccharide unique to Gram-negatives
D. Mycolic acids of the acid-fast envelope
Correct Answer: A
Rationale:
Capsules are typically polysaccharide (or polypeptide) layers outside the wall that impede phagocytosis.
Q4. An organism lacks a nucleus and membrane-bound organelles but has 70S ribosomes and a circular chromosome. It belongs to:
A. Eukarya
B. Viruses
C. Bacteria or Archaea
D. Fungi
Correct Answer: C
Rationale:
Prokaryotes (Bacteria and Archaea) lack nuclei and membrane-bound organelles and possess 70S ribosomes and circular chromosomes.
Q5. In an endospore stain, green structures inside pink vegetative cells represent:
A. Endospores that are highly resistant to stress
B. Capsules
C. Flagella
D. Nucleoids
Correct Answer: A
Rationale:
Malachite green stains endospores; safranin counterstains vegetative cells pink/red.
Q6. Pili that mediate attachment to host cells are composed of:
A. Flagellin
B. Peptidoglycan subunits
C. Pilin protein subunits
D. Lipid A
Correct Answer: C
Rationale:
Pili (fimbriae) are built from pilin subunits and function mainly in adhesion.
STUVIA ACTUAL EXAM · Page 2
, SECTION 1: Microbial Cell Structure, Microscopy & Classification
Q7. A bacterial cell placed in a hypertonic solution undergoes plasmolysis because:
A. Water leaves and the cytoplasm shrinks from the wall
B. Water enters and the cell lyses
C. The wall dissolves completely
D. Active transport pumps solutes inward
Correct Answer: A
Rationale:
Hypertonic conditions cause water efflux and plasmolysis.
Q8. EDTA is required with lysozyme to produce spheroplasts from Gram-negative cells because it:
A. Destabilizes the outer membrane so lysozyme can reach peptidoglycan
B. Digests thick peptidoglycan
C. Inhibits 70S ribosomes
D. Cross-links peptide side chains
Correct Answer: A
Rationale:
EDTA chelates cations that stabilize the outer membrane, allowing lysozyme access.
Q9. The difference between bacterial 70S and eukaryotic 80S ribosomes is clinically important because it:
A. Makes all antibiotics equally toxic to host cells
B. Means bacteria lack ribosomes
C. Means eukaryotic cells have no protein synthesis
D. Allows selective antibiotic toxicity against bacterial protein synthesis
Correct Answer: D
Rationale:
Structural differences between 70S and 80S ribosomes permit selective inhibition by many antibiotics.
Q10. Acid-fast organisms resist acid-alcohol decolorization because of:
A. Thick peptidoglycan alone
B. Mycolic acids that create a waxy impermeable barrier
C. An outer membrane of LPS
D. Absence of any cell wall
Correct Answer: B
Rationale:
Mycolic acids confer the acid-fast property.
Q11. Corkscrew motility of spirochetes is produced by:
A. Peritrichous flagella
B. Pili that twitch
C. Eukaryotic-style cilia
D. Axial filaments (endoflagella) in the periplasm
Correct Answer: D
Rationale:
Spirochetes use periplasmic axial filaments for characteristic motility.
Q12. Isolation of pure colonies on solid medium is achieved by the:
A. Broth dilution method
B. Streak-plate method that progressively dilutes the inoculum
C. Direct microscopic count
D. Turbidimetric OD measurement
Correct Answer: B
Rationale:
Streak plating spatially dilutes cells so individual colonies arise from single CFUs.
STUVIA ACTUAL EXAM · Page 3
