BIO 250 Final Exam V3 | BIO 250
Microbiology | Actual Q&A with Rationale
(BIO250 Final Exam) | StraighterLine
1. Which of the following is a primary characteristic of the domain Archaea that distinguishes
it from Bacteria?
A. The presence of a true nucleus.
B. The use of 70S ribosomes.
C. The lack of peptidoglycan in their cell walls.
D. The presence of membrane-bound organelles.
Answer: C
Rationale: Archaea are prokaryotic organisms that lack peptidoglycan in their cell walls,
which is a defining feature of Bacteria. While both domains have 70S ribosomes, their
chemical compositions and sequences are distinct. This fundamental difference in cell wall
structure is a major reason why they are categorized into separate domains in the three-
domain system.
2. In the Gram staining procedure, what is the specific role of Safranin?
A. To act as a primary stain for thick peptidoglycan.
B. To function as a mordant to stabilize crystal violet.
C. To dehydrate the cell wall of Gram-positive cells.
,D. To act as a counterstain for Gram-negative cells.
Answer: D
Rationale: Safranin is used as a counterstain to provide color to Gram-negative bacteria
after they have been decolorized by alcohol. Because Gram-negative cells have a thin
peptidoglycan layer, they lose the crystal violet-iodine complex. This allows the red or pink
safranin to be visible under a microscope, distinguishing them from the purple Gram-
positive cells.
3. Which of the following structures or features are typically associated with prokaryotic cell
morphology and physiology? (Select all that apply)
A. 70S Ribosomes
B. Nucleoid region
C. Endoplasmic Reticulum
D. Binary Fission
E. Circular Chromosome
F. 80S Ribosomes
Answer: A, B, D, E
Rationale: Prokaryotic cells are characterized by having a nucleoid region where genetic
material is located rather than a membrane-bound nucleus. They possess 70S ribosomes
for protein synthesis and typically have a single circular chromosome. Additionally, they
, reproduce primarily through binary fission, an asexual process that results in two identical
daughter cells.
4. A bacterial cell that requires organic molecules for both its carbon and energy source is
classified as a:
A. Photoautotroph
B. Chemoautotroph
C. Chemoheterotroph
D. Photoheterotroph
Answer: C
Rationale: Chemoheterotrophs are organisms that derive energy from chemical reactions
and carbon from organic compounds. This category includes most bacteria, as well as all
animals, fungi, and protozoa. Understanding these metabolic classifications is essential for
predicting the growth environment and ecological niche of a specific microbe.
5. What occurs during the ‘Lag Phase’ of a standard bacterial growth curve?
A. Rapid cellular division and metabolic activity.
B. Depletion of nutrients leading to spore formation.
C. Equilibrium between cell death and cell production.
D. Preparation for growth including synthesis of enzymes.
Answer: D
Microbiology | Actual Q&A with Rationale
(BIO250 Final Exam) | StraighterLine
1. Which of the following is a primary characteristic of the domain Archaea that distinguishes
it from Bacteria?
A. The presence of a true nucleus.
B. The use of 70S ribosomes.
C. The lack of peptidoglycan in their cell walls.
D. The presence of membrane-bound organelles.
Answer: C
Rationale: Archaea are prokaryotic organisms that lack peptidoglycan in their cell walls,
which is a defining feature of Bacteria. While both domains have 70S ribosomes, their
chemical compositions and sequences are distinct. This fundamental difference in cell wall
structure is a major reason why they are categorized into separate domains in the three-
domain system.
2. In the Gram staining procedure, what is the specific role of Safranin?
A. To act as a primary stain for thick peptidoglycan.
B. To function as a mordant to stabilize crystal violet.
C. To dehydrate the cell wall of Gram-positive cells.
,D. To act as a counterstain for Gram-negative cells.
Answer: D
Rationale: Safranin is used as a counterstain to provide color to Gram-negative bacteria
after they have been decolorized by alcohol. Because Gram-negative cells have a thin
peptidoglycan layer, they lose the crystal violet-iodine complex. This allows the red or pink
safranin to be visible under a microscope, distinguishing them from the purple Gram-
positive cells.
3. Which of the following structures or features are typically associated with prokaryotic cell
morphology and physiology? (Select all that apply)
A. 70S Ribosomes
B. Nucleoid region
C. Endoplasmic Reticulum
D. Binary Fission
E. Circular Chromosome
F. 80S Ribosomes
Answer: A, B, D, E
Rationale: Prokaryotic cells are characterized by having a nucleoid region where genetic
material is located rather than a membrane-bound nucleus. They possess 70S ribosomes
for protein synthesis and typically have a single circular chromosome. Additionally, they
, reproduce primarily through binary fission, an asexual process that results in two identical
daughter cells.
4. A bacterial cell that requires organic molecules for both its carbon and energy source is
classified as a:
A. Photoautotroph
B. Chemoautotroph
C. Chemoheterotroph
D. Photoheterotroph
Answer: C
Rationale: Chemoheterotrophs are organisms that derive energy from chemical reactions
and carbon from organic compounds. This category includes most bacteria, as well as all
animals, fungi, and protozoa. Understanding these metabolic classifications is essential for
predicting the growth environment and ecological niche of a specific microbe.
5. What occurs during the ‘Lag Phase’ of a standard bacterial growth curve?
A. Rapid cellular division and metabolic activity.
B. Depletion of nutrients leading to spore formation.
C. Equilibrium between cell death and cell production.
D. Preparation for growth including synthesis of enzymes.
Answer: D
