BIOD 171 Microbiology Final Exam Actual Exam
2026/2027 – Portage Learning – Verified
Answers with Detailed Rationales – Pass
Guaranteed – A+ Graded
======================================================
========== SECTION 1: MICROBIAL STRUCTURE & FUNCTION (12
Questions)
Q1: Which of the following structures is found in Gram-negative bacteria but NOT in
Gram-positive bacteria?
A. Peptidoglycan
B. Plasma membrane
C. Lipopolysaccharide (LPS) [CORRECT]
D. Ribosomes
Correct Answer: C
Rationale: Key concept: Gram-negative cell wall structure includes an outer membrane
containing LPS. Correct answer: LPS (endotoxin) is unique to Gram-negative bacteria
and is not present in Gram-positive bacteria. A is wrong: Both Gram-positive and
Gram-negative bacteria have peptidoglycan (Gram-positive has a thick layer;
Gram-negative has a thin layer). B is wrong: Both have a plasma membrane
(cytoplasmic membrane). D is wrong: Both have 70S ribosomes.
Q2: A microbiologist performs a Gram stain on an unknown bacterial sample. After
completing the procedure, she observes purple, spherical cells arranged in clusters
under the microscope. What is the correct description of this organism?
A. Gram-negative bacilli
B. Gram-positive cocci [CORRECT]
C. Gram-negative cocci
,D. Gram-positive bacilli
Correct Answer: B
Rationale: Key concept: Gram stain results (purple = Gram-positive; pink =
Gram-negative) and morphology (spherical = cocci; rod-shaped = bacilli). Correct
answer: Purple = Gram-positive; spherical = cocci; clusters = staphylo- arrangement. A is
wrong: Gram-negative would appear pink, not purple. C is wrong: Gram-negative cocci
would be pink. D is wrong: Gram-positive bacilli would be purple rods.
Q3: Mycobacterium tuberculosis has an acid-fast cell wall containing mycolic acid. This
property makes the organism resistant to:
A. Gram staining
B. Decolorization by acid-alcohol after staining with carbolfuchsin [CORRECT]
C. All forms of disinfection
D. Phagocytosis by macrophages
Correct Answer: B
Rationale: Key concept: Acid-fast staining property due to mycolic acid in cell wall.
Correct answer: The waxy mycolic acid retains carbolfuchsin dye despite acid-alcohol
decolorization, appearing red. A is wrong: Acid-fast bacteria can be Gram stained
(poorly), but acid-fast staining is different. C is wrong: While resistant, they are not
resistant to all disinfection (e.g., autoclaving kills them). D is wrong: While mycolic acid
provides some protection, macrophages can phagocytose M. tuberculosis.
Q4: Which cellular structure provides bacteria with resistance to desiccation (drying)
and helps evade phagocytosis?
A. Flagella
B. Capsule [CORRECT]
C. Pili
D. Plasmid
Correct Answer: B
Rationale: Key concept: Bacterial capsule structure and function. Correct answer: The
polysaccharide capsule prevents drying and inhibits phagocytosis by masking bacterial
antigens. A is wrong: Flagella provide motility, not desiccation resistance. C is wrong:
,Pili are for attachment and conjugation. D is wrong: Plasmids are extrachromosomal
DNA for genetic traits, not physical protection.
Q5: A bacterial cell with peritrichous flagella exhibits which type of motility?
A. Tumbling motion in one place
B. "Run and tumble" movement with flagella distributed over the entire cell surface
[CORRECT]
C. Movement in a single direction only
D. Gliding motility without flagellar rotation
Correct Answer: B
Rationale: Key concept: Flagellar arrangement and motility patterns. Correct answer:
Peritrichous flagella project in all directions, allowing counterclockwise rotation for
"runs" and clockwise for "tumbles." A is wrong: Tumbling alone describes partial
flagellar action. C is wrong: Unidirectional movement occurs with polar flagella in
monotrichous or lophotrichous arrangements. D is wrong: Gliding motility occurs
without flagella in certain bacteria.
Q6: Which statement correctly distinguishes prokaryotic from eukaryotic ribosomes?
A. Prokaryotic ribosomes are 80S; eukaryotic ribosomes are 70S
B. Prokaryotic ribosomes are 70S; eukaryotic ribosomes are 80S [CORRECT]
C. Both have 70S ribosomes
D. Both have 80S ribosomes
Correct Answer: B
Rationale: Key concept: Ribosome sedimentation coefficients (Svedberg units). Correct
answer: Prokaryotes have 70S ribosomes (50S + 30S subunits); eukaryotes have 80S
ribosomes (60S + 40S subunits). A is wrong: It reverses the values. C is wrong: Only
prokaryotes and organelles have 70S. D is wrong: Only eukaryotic cytoplasmic
ribosomes are 80S.
Q7: A spherical bacterium arranged in chains resembling a string of pearls is described
as:
A. Staphylococci
B. Streptococci [CORRECT]
C. Diplococci
, D. Sarcinae
Correct Answer: B
Rationale: Key concept: Bacterial arrangement terminology. Correct answer: Strepto-
indicates chain formation; cocci indicates spherical shape. A is wrong: Staphylo-
indicates cluster formation (like grapes). C is wrong: Diplo- indicates pairs. D is wrong:
Sarcinae indicates cubical packets of eight cells.
Q8: The periplasmic space in Gram-negative bacteria:
A. Contains the peptidoglycan layer and various degradative enzymes [CORRECT]
B. Is found between the plasma membrane and the inner membrane
C. Contains teichoic acids
D. Is absent in all bacteria
Correct Answer: A
Rationale: Key concept: Gram-negative cell wall architecture. Correct answer: The
periplasm is the space between the outer membrane and plasma membrane containing
thin peptidoglycan and enzymes. B is wrong: The outer membrane is the outermost
structure; there is no "inner membrane" in this context. C is wrong: Teichoic acids are
found in Gram-positive cell walls, not the periplasmic space. D is wrong: While absent in
Gram-positives, it is a defining feature of Gram-negatives.
Q9: Which structure allows bacteria to attach to surfaces and to other bacteria for the
exchange of genetic material?
A. Capsule
B. Fimbriae
C. Sex pili [CORRECT]
D. Flagella
Correct Answer: C
Rationale: Key concept: Pili types and functions. Correct answer: Sex pili (conjugation
pili) facilitate attachment for conjugation and DNA transfer. A is wrong: Capsules
provide protection, not genetic exchange. B is wrong: Fimbriae are for attachment to
surfaces but not specifically for DNA exchange. D is wrong: Flagella are for motility.
Q10: Endospores are significant in microbiology because they:
A. Are reproductive structures produced in large numbers
2026/2027 – Portage Learning – Verified
Answers with Detailed Rationales – Pass
Guaranteed – A+ Graded
======================================================
========== SECTION 1: MICROBIAL STRUCTURE & FUNCTION (12
Questions)
Q1: Which of the following structures is found in Gram-negative bacteria but NOT in
Gram-positive bacteria?
A. Peptidoglycan
B. Plasma membrane
C. Lipopolysaccharide (LPS) [CORRECT]
D. Ribosomes
Correct Answer: C
Rationale: Key concept: Gram-negative cell wall structure includes an outer membrane
containing LPS. Correct answer: LPS (endotoxin) is unique to Gram-negative bacteria
and is not present in Gram-positive bacteria. A is wrong: Both Gram-positive and
Gram-negative bacteria have peptidoglycan (Gram-positive has a thick layer;
Gram-negative has a thin layer). B is wrong: Both have a plasma membrane
(cytoplasmic membrane). D is wrong: Both have 70S ribosomes.
Q2: A microbiologist performs a Gram stain on an unknown bacterial sample. After
completing the procedure, she observes purple, spherical cells arranged in clusters
under the microscope. What is the correct description of this organism?
A. Gram-negative bacilli
B. Gram-positive cocci [CORRECT]
C. Gram-negative cocci
,D. Gram-positive bacilli
Correct Answer: B
Rationale: Key concept: Gram stain results (purple = Gram-positive; pink =
Gram-negative) and morphology (spherical = cocci; rod-shaped = bacilli). Correct
answer: Purple = Gram-positive; spherical = cocci; clusters = staphylo- arrangement. A is
wrong: Gram-negative would appear pink, not purple. C is wrong: Gram-negative cocci
would be pink. D is wrong: Gram-positive bacilli would be purple rods.
Q3: Mycobacterium tuberculosis has an acid-fast cell wall containing mycolic acid. This
property makes the organism resistant to:
A. Gram staining
B. Decolorization by acid-alcohol after staining with carbolfuchsin [CORRECT]
C. All forms of disinfection
D. Phagocytosis by macrophages
Correct Answer: B
Rationale: Key concept: Acid-fast staining property due to mycolic acid in cell wall.
Correct answer: The waxy mycolic acid retains carbolfuchsin dye despite acid-alcohol
decolorization, appearing red. A is wrong: Acid-fast bacteria can be Gram stained
(poorly), but acid-fast staining is different. C is wrong: While resistant, they are not
resistant to all disinfection (e.g., autoclaving kills them). D is wrong: While mycolic acid
provides some protection, macrophages can phagocytose M. tuberculosis.
Q4: Which cellular structure provides bacteria with resistance to desiccation (drying)
and helps evade phagocytosis?
A. Flagella
B. Capsule [CORRECT]
C. Pili
D. Plasmid
Correct Answer: B
Rationale: Key concept: Bacterial capsule structure and function. Correct answer: The
polysaccharide capsule prevents drying and inhibits phagocytosis by masking bacterial
antigens. A is wrong: Flagella provide motility, not desiccation resistance. C is wrong:
,Pili are for attachment and conjugation. D is wrong: Plasmids are extrachromosomal
DNA for genetic traits, not physical protection.
Q5: A bacterial cell with peritrichous flagella exhibits which type of motility?
A. Tumbling motion in one place
B. "Run and tumble" movement with flagella distributed over the entire cell surface
[CORRECT]
C. Movement in a single direction only
D. Gliding motility without flagellar rotation
Correct Answer: B
Rationale: Key concept: Flagellar arrangement and motility patterns. Correct answer:
Peritrichous flagella project in all directions, allowing counterclockwise rotation for
"runs" and clockwise for "tumbles." A is wrong: Tumbling alone describes partial
flagellar action. C is wrong: Unidirectional movement occurs with polar flagella in
monotrichous or lophotrichous arrangements. D is wrong: Gliding motility occurs
without flagella in certain bacteria.
Q6: Which statement correctly distinguishes prokaryotic from eukaryotic ribosomes?
A. Prokaryotic ribosomes are 80S; eukaryotic ribosomes are 70S
B. Prokaryotic ribosomes are 70S; eukaryotic ribosomes are 80S [CORRECT]
C. Both have 70S ribosomes
D. Both have 80S ribosomes
Correct Answer: B
Rationale: Key concept: Ribosome sedimentation coefficients (Svedberg units). Correct
answer: Prokaryotes have 70S ribosomes (50S + 30S subunits); eukaryotes have 80S
ribosomes (60S + 40S subunits). A is wrong: It reverses the values. C is wrong: Only
prokaryotes and organelles have 70S. D is wrong: Only eukaryotic cytoplasmic
ribosomes are 80S.
Q7: A spherical bacterium arranged in chains resembling a string of pearls is described
as:
A. Staphylococci
B. Streptococci [CORRECT]
C. Diplococci
, D. Sarcinae
Correct Answer: B
Rationale: Key concept: Bacterial arrangement terminology. Correct answer: Strepto-
indicates chain formation; cocci indicates spherical shape. A is wrong: Staphylo-
indicates cluster formation (like grapes). C is wrong: Diplo- indicates pairs. D is wrong:
Sarcinae indicates cubical packets of eight cells.
Q8: The periplasmic space in Gram-negative bacteria:
A. Contains the peptidoglycan layer and various degradative enzymes [CORRECT]
B. Is found between the plasma membrane and the inner membrane
C. Contains teichoic acids
D. Is absent in all bacteria
Correct Answer: A
Rationale: Key concept: Gram-negative cell wall architecture. Correct answer: The
periplasm is the space between the outer membrane and plasma membrane containing
thin peptidoglycan and enzymes. B is wrong: The outer membrane is the outermost
structure; there is no "inner membrane" in this context. C is wrong: Teichoic acids are
found in Gram-positive cell walls, not the periplasmic space. D is wrong: While absent in
Gram-positives, it is a defining feature of Gram-negatives.
Q9: Which structure allows bacteria to attach to surfaces and to other bacteria for the
exchange of genetic material?
A. Capsule
B. Fimbriae
C. Sex pili [CORRECT]
D. Flagella
Correct Answer: C
Rationale: Key concept: Pili types and functions. Correct answer: Sex pili (conjugation
pili) facilitate attachment for conjugation and DNA transfer. A is wrong: Capsules
provide protection, not genetic exchange. B is wrong: Fimbriae are for attachment to
surfaces but not specifically for DNA exchange. D is wrong: Flagella are for motility.
Q10: Endospores are significant in microbiology because they:
A. Are reproductive structures produced in large numbers
