WGU D311 Microbiology with Lab: 100 Final Exam
Review Questions with Answers & Rationales (2026)
## Section 1: Microbial Structure and Function
**1. Which component is found specifically in bacterial cell walls but not in archaea or
eukaryotes?**
**Answer: Peptidoglycan**
Rationale: Peptidoglycan is a unique polymer of sugars and amino acids forming a mesh-like
layer outside the plasma membrane of most bacteria.
**2. Why are archaea considered prokaryotic organisms?**
**Answer: Their cells do not contain a nucleus**
Rationale: Prokaryotes are defined by the absence of a membrane-bound nucleus.
**3. What is the significance of phospholipids in the plasma membrane?**
**Answer: They maintain hydrophobic and hydrophilic environments**
Rationale: The phospholipid bilayer creates a barrier with hydrophilic heads facing outward and
hydrophobic tails facing inward.
**4. Which structure is unique to Gram-negative bacteria and contains lipid A?**
**Answer: Outer membrane**
Rationale: The outer membrane contains lipopolysaccharides (LPS), with lipid A being the toxic
endotoxin component.
**5. Which structure determines the different outcomes of the Gram stain?**
,**Answer: Peptidoglycan**
Rationale: Gram-positive bacteria have thick peptidoglycan that retains crystal violet; Gram-
negative have thin peptidoglycan.
**6. A bacterium with a capsule is more pathogenic because:**
**Answer: The capsule helps resist phagocytosis**
Rationale: The capsule's slippery nature makes it difficult for phagocytes to engulf the
bacterium.
**7. Which structure is responsible for bacterial motility and is composed of flagellin?**
**Answer: Flagella**
Rationale: Flagella are whip-like appendages made of flagellin that rotate to propel bacteria.
**8. Fimbriae and pili are primarily used for:**
**Answer: Adhering to host tissues**
Rationale: These short hair-like structures allow pathogens to attach to host cells and resist
being flushed away.
**9. Why are viruses considered acellular?**
**Answer: They lack a cell membrane and cannot reproduce independently**
Rationale: Viruses are not cells; they must hijack host cell machinery to replicate.
**10. Which class of cells most often contain plasmids?**
**Answer: Prokaryotic**
Rationale: Plasmids are extrachromosomal DNA found primarily in prokaryotes.
**11. What is the macromolecular network that makes up bacterial cell walls?**
, **Answer: Peptidoglycan**
Rationale: Peptidoglycan provides structural support and osmotic protection.
**12. Which type of bacterial cell wall contains an outer membrane?**
**Answer: Gram-negative**
Rationale: The outer membrane is a distinguishing feature of Gram-negative bacteria.
**13. What kind of ribosomes are found in prokaryotic cells?**
**Answer: 70S**
Rationale: Prokaryotic ribosomes are 70S, while eukaryotic ribosomes are 80S.
**14. A rigid spiral-shaped bacterium is called a:**
**Answer: Spirillum**
Rationale: Spirillum describes a rigid spiral shape.
**15. The slimy polysaccharide matrix outside a cell is called:**
**Answer: Glycocalyx**
Rationale: The glycocalyx protects and helps bacteria adhere to surfaces.
---
## Section 2: Microscopy and Staining
**16. What does a phase-contrast microscope use to visualize a specimen?**
**Answer: Light**
Review Questions with Answers & Rationales (2026)
## Section 1: Microbial Structure and Function
**1. Which component is found specifically in bacterial cell walls but not in archaea or
eukaryotes?**
**Answer: Peptidoglycan**
Rationale: Peptidoglycan is a unique polymer of sugars and amino acids forming a mesh-like
layer outside the plasma membrane of most bacteria.
**2. Why are archaea considered prokaryotic organisms?**
**Answer: Their cells do not contain a nucleus**
Rationale: Prokaryotes are defined by the absence of a membrane-bound nucleus.
**3. What is the significance of phospholipids in the plasma membrane?**
**Answer: They maintain hydrophobic and hydrophilic environments**
Rationale: The phospholipid bilayer creates a barrier with hydrophilic heads facing outward and
hydrophobic tails facing inward.
**4. Which structure is unique to Gram-negative bacteria and contains lipid A?**
**Answer: Outer membrane**
Rationale: The outer membrane contains lipopolysaccharides (LPS), with lipid A being the toxic
endotoxin component.
**5. Which structure determines the different outcomes of the Gram stain?**
,**Answer: Peptidoglycan**
Rationale: Gram-positive bacteria have thick peptidoglycan that retains crystal violet; Gram-
negative have thin peptidoglycan.
**6. A bacterium with a capsule is more pathogenic because:**
**Answer: The capsule helps resist phagocytosis**
Rationale: The capsule's slippery nature makes it difficult for phagocytes to engulf the
bacterium.
**7. Which structure is responsible for bacterial motility and is composed of flagellin?**
**Answer: Flagella**
Rationale: Flagella are whip-like appendages made of flagellin that rotate to propel bacteria.
**8. Fimbriae and pili are primarily used for:**
**Answer: Adhering to host tissues**
Rationale: These short hair-like structures allow pathogens to attach to host cells and resist
being flushed away.
**9. Why are viruses considered acellular?**
**Answer: They lack a cell membrane and cannot reproduce independently**
Rationale: Viruses are not cells; they must hijack host cell machinery to replicate.
**10. Which class of cells most often contain plasmids?**
**Answer: Prokaryotic**
Rationale: Plasmids are extrachromosomal DNA found primarily in prokaryotes.
**11. What is the macromolecular network that makes up bacterial cell walls?**
, **Answer: Peptidoglycan**
Rationale: Peptidoglycan provides structural support and osmotic protection.
**12. Which type of bacterial cell wall contains an outer membrane?**
**Answer: Gram-negative**
Rationale: The outer membrane is a distinguishing feature of Gram-negative bacteria.
**13. What kind of ribosomes are found in prokaryotic cells?**
**Answer: 70S**
Rationale: Prokaryotic ribosomes are 70S, while eukaryotic ribosomes are 80S.
**14. A rigid spiral-shaped bacterium is called a:**
**Answer: Spirillum**
Rationale: Spirillum describes a rigid spiral shape.
**15. The slimy polysaccharide matrix outside a cell is called:**
**Answer: Glycocalyx**
Rationale: The glycocalyx protects and helps bacteria adhere to surfaces.
---
## Section 2: Microscopy and Staining
**16. What does a phase-contrast microscope use to visualize a specimen?**
**Answer: Light**
