Microbiology BIO 420 Exam 1| Contains
Questions with Verified Correct Answers|
Already Graded A+
1. Who is credited with first observing “animalcules” under a simple
microscope?
A. Robert Hooke
B. Louis Pasteur
C. Antonie van Leeuwenhoek
D. Francesco Redi
Correct ,,answer,,,: C. Antonie van Leeuwenhoek
Rationale: Leeuwenhoek (1632–1723) built simple microscopes and first
described bacteria and protozoa, calling them “animalcules.”
2. The theory that living organisms can arise from nonliving matter is called:
A. Biogenesis
B. Spontaneous generation
C. Germ theory
D. Cell theory
Correct ,,answer,,,: B. Spontaneous generation
Rationale: Spontaneous generation was the prevailing idea until Pasteur’s
experiments disproved it.
3. Which scientist’s swan-neck flask experiment definitively disproved
spontaneous generation?
A. John Tyndall
,B. Robert Koch
C. Louis Pasteur
D. Joseph Lister
Correct ,,answer,,,: C. Louis Pasteur
Rationale: Pasteur’s swan-neck flasks showed that broth remained sterile unless
dust (with microbes) entered.
4. Koch’s postulates are used to:
A. Classify bacteria by shape
B. Identify the causative agent of a disease
C. Stain bacterial endospores
D. Isolate viruses
Correct ,,answer,,,: B. Identify the causative agent of a disease
Rationale: Koch’s postulates link a specific microorganism to a specific disease.
5. Which of the following is a limitation of Koch’s postulates?
A. Cannot be used for bacteria
B. Requires the use of an electron microscope
C. Some pathogens cannot be cultured in artificial media
D. They only apply to fungal infections
Correct ,,answer,,,: C. Some pathogens cannot be cultured in artificial media
Rationale: Many pathogens (e.g., Treponema pallidum) cannot be grown on
artificial media, making Koch’s postulates impractical.
6. The resolution of a microscope is defined as:
A. The ability to magnify an object
B. The ability to distinguish two adjacent objects as separate
C. The ability to increase contrast
D. The product of ocular and objective lens powers
,Correct ,,answer,,,: B. The ability to distinguish two adjacent objects as separate
Rationale: Resolution (resolving power) is the minimum distance between two
points that can be seen as distinct.
7. Which type of microscopy uses ultraviolet light to excite fluorescent
molecules?
A. Phase-contrast
B. Dark-field
C. Fluorescence microscopy
D. Bright-field
Correct ,,answer,,,: C. Fluorescence microscopy
Rationale: Fluorescence microscopy uses UV or blue light to excite fluorophores,
which then emit visible light.
8. The total magnification of a compound light microscope with a 10x ocular
and a 40x objective is:
A. 50x
B. 400x
C. 1000x
D. 40x
Correct ,,answer,,,: B. 400x
Rationale: Total magnification = ocular × objective = 10 × 40 = 400.
9. Which structure is present in all bacteria?
A. Nucleus
B. Mitochondria
C. Cell membrane
D. Endoplasmic reticulum
, Correct ,,answer,,,: C. Cell membrane
Rationale: All bacteria have a cell membrane (plasma membrane). They lack
membrane-bound organelles.
10. The bacterial cell wall is primarily composed of:
A. Cellulose
B. Chitin
C. Peptidoglycan
D. Lipopolysaccharide
Correct ,,answer,,,: C. Peptidoglycan
Rationale: Peptidoglycan (murein) is a polymer of sugars and amino acids unique
to bacteria.
11. Gram-positive bacteria stain purple because:
A. They have a thin peptidoglycan layer and lose the crystal violet-iodine complex
B. They have a thick peptidoglycan layer that retains the crystal violet-iodine
complex
C. They take up the safranin counterstain
D. They lack a cell wall
Correct ,,answer,,,: B. They have a thick peptidoglycan layer that retains the
crystal violet-iodine complex
Rationale: The thick peptidoglycan traps the crystal violet after alcohol
decolorization.
12. Gram-negative bacteria appear pink after Gram staining because:
A. Their thick peptidoglycan retains crystal violet
B. Their outer membrane is disrupted by alcohol, allowing crystal violet to wash
out, and they take up safranin
C. They contain no peptidoglycan
D. They have a capsule that binds safranin
Questions with Verified Correct Answers|
Already Graded A+
1. Who is credited with first observing “animalcules” under a simple
microscope?
A. Robert Hooke
B. Louis Pasteur
C. Antonie van Leeuwenhoek
D. Francesco Redi
Correct ,,answer,,,: C. Antonie van Leeuwenhoek
Rationale: Leeuwenhoek (1632–1723) built simple microscopes and first
described bacteria and protozoa, calling them “animalcules.”
2. The theory that living organisms can arise from nonliving matter is called:
A. Biogenesis
B. Spontaneous generation
C. Germ theory
D. Cell theory
Correct ,,answer,,,: B. Spontaneous generation
Rationale: Spontaneous generation was the prevailing idea until Pasteur’s
experiments disproved it.
3. Which scientist’s swan-neck flask experiment definitively disproved
spontaneous generation?
A. John Tyndall
,B. Robert Koch
C. Louis Pasteur
D. Joseph Lister
Correct ,,answer,,,: C. Louis Pasteur
Rationale: Pasteur’s swan-neck flasks showed that broth remained sterile unless
dust (with microbes) entered.
4. Koch’s postulates are used to:
A. Classify bacteria by shape
B. Identify the causative agent of a disease
C. Stain bacterial endospores
D. Isolate viruses
Correct ,,answer,,,: B. Identify the causative agent of a disease
Rationale: Koch’s postulates link a specific microorganism to a specific disease.
5. Which of the following is a limitation of Koch’s postulates?
A. Cannot be used for bacteria
B. Requires the use of an electron microscope
C. Some pathogens cannot be cultured in artificial media
D. They only apply to fungal infections
Correct ,,answer,,,: C. Some pathogens cannot be cultured in artificial media
Rationale: Many pathogens (e.g., Treponema pallidum) cannot be grown on
artificial media, making Koch’s postulates impractical.
6. The resolution of a microscope is defined as:
A. The ability to magnify an object
B. The ability to distinguish two adjacent objects as separate
C. The ability to increase contrast
D. The product of ocular and objective lens powers
,Correct ,,answer,,,: B. The ability to distinguish two adjacent objects as separate
Rationale: Resolution (resolving power) is the minimum distance between two
points that can be seen as distinct.
7. Which type of microscopy uses ultraviolet light to excite fluorescent
molecules?
A. Phase-contrast
B. Dark-field
C. Fluorescence microscopy
D. Bright-field
Correct ,,answer,,,: C. Fluorescence microscopy
Rationale: Fluorescence microscopy uses UV or blue light to excite fluorophores,
which then emit visible light.
8. The total magnification of a compound light microscope with a 10x ocular
and a 40x objective is:
A. 50x
B. 400x
C. 1000x
D. 40x
Correct ,,answer,,,: B. 400x
Rationale: Total magnification = ocular × objective = 10 × 40 = 400.
9. Which structure is present in all bacteria?
A. Nucleus
B. Mitochondria
C. Cell membrane
D. Endoplasmic reticulum
, Correct ,,answer,,,: C. Cell membrane
Rationale: All bacteria have a cell membrane (plasma membrane). They lack
membrane-bound organelles.
10. The bacterial cell wall is primarily composed of:
A. Cellulose
B. Chitin
C. Peptidoglycan
D. Lipopolysaccharide
Correct ,,answer,,,: C. Peptidoglycan
Rationale: Peptidoglycan (murein) is a polymer of sugars and amino acids unique
to bacteria.
11. Gram-positive bacteria stain purple because:
A. They have a thin peptidoglycan layer and lose the crystal violet-iodine complex
B. They have a thick peptidoglycan layer that retains the crystal violet-iodine
complex
C. They take up the safranin counterstain
D. They lack a cell wall
Correct ,,answer,,,: B. They have a thick peptidoglycan layer that retains the
crystal violet-iodine complex
Rationale: The thick peptidoglycan traps the crystal violet after alcohol
decolorization.
12. Gram-negative bacteria appear pink after Gram staining because:
A. Their thick peptidoglycan retains crystal violet
B. Their outer membrane is disrupted by alcohol, allowing crystal violet to wash
out, and they take up safranin
C. They contain no peptidoglycan
D. They have a capsule that binds safranin
