Microbiology BIO 420 Exam 1 |
Contains Questions with Verified
Correct Answers | Already Graded A+
1. Who is credited with first observing “animalcules” under a microscope?
A. Robert Hooke
B. Louis Pasteur
C. Antonie van Leeuwenhoek
D. Francesco Redi
Correct answer: C. Antonie van Leeuwenhoek
Rationale: Leeuwenhoek 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. Cell theory
D. Germ theory
Correct answer: B. Spontaneous generation
Rationale: Spontaneous generation was the prevailing idea until Pasteur’s
experiments disproved it.
3. Which statement is most accurate regarding viruses?
A. “This is a new species of bacteria.”
B. “This is a new species of protozoa.”
C. “This is a new species of virus.”
D. “This is a new species of fungus.”
Correct answer: C. “This is a new species of virus.”
Rationale: Viruses are not considered living organisms because they lack
metabolism and independent reproduction, but they are still classified as “species”
in virology.
,4. Who disproved spontaneous generation using swan-neck flasks?
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.
5. 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.
6. 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, some viruses) cannot be
grown on artificial media, limiting Koch’s postulates.
7. 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.
8. Which type of microscopy uses ultraviolet light to excite fluorophores?
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.
9. 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 = 400x.
10. Which of the following is present in ALL bacteria?
A. Cell wall
B. Nucleus
C. Cell membrane
D. Endospore
Correct answer: C. Cell membrane
Rationale: All bacteria have a cell membrane (plasma membrane). They lack
membrane-bound organelles. Some bacteria lack a cell wall (Mycoplasma).
11. 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 (NAG/NAM) and amino
acids, unique to bacteria.
12. 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: Gram-positive cells have multiple layers of peptidoglycan that trap the
crystal violet-iodine complex after decolorization.
13. Gram-negative bacteria appear pink because:
A. They lack a cell wall.
B. Their thin peptidoglycan cannot retain the crystal violet-iodine complex and
they take up safranin.
C. They have a thick layer of lipopolysaccharide.
D. They are stained only by the primary stain.
Correct answer: B. Their thin peptidoglycan cannot retain the crystal violet-
iodine complex and they take up safranin.
Rationale: Alcohol dissolves the outer membrane and washes out crystal violet;
safranin counterstains the now colorless cells.
14. The outer membrane of Gram-negative bacteria contains:
A. Teichoic acid
B. Lipopolysaccharide (LPS)
C. Peptidoglycan only
D. Mycolic acid
Correct answer: B. Lipopolysaccharide (LPS)
Rationale: LPS is the major component of the outer membrane and acts as an
endotoxin.
15. Which bacterial structure is responsible for attachment to surfaces and is
involved in biofilm formation?
A. Flagella
B. Pili (fimbriae)
C. Ribosomes
D. Endospores
Correct answer: B. Pili (fimbriae)
Rationale: Fimbriae are short, hair-like structures that mediate adherence to
surfaces and host cells.
Contains Questions with Verified
Correct Answers | Already Graded A+
1. Who is credited with first observing “animalcules” under a microscope?
A. Robert Hooke
B. Louis Pasteur
C. Antonie van Leeuwenhoek
D. Francesco Redi
Correct answer: C. Antonie van Leeuwenhoek
Rationale: Leeuwenhoek 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. Cell theory
D. Germ theory
Correct answer: B. Spontaneous generation
Rationale: Spontaneous generation was the prevailing idea until Pasteur’s
experiments disproved it.
3. Which statement is most accurate regarding viruses?
A. “This is a new species of bacteria.”
B. “This is a new species of protozoa.”
C. “This is a new species of virus.”
D. “This is a new species of fungus.”
Correct answer: C. “This is a new species of virus.”
Rationale: Viruses are not considered living organisms because they lack
metabolism and independent reproduction, but they are still classified as “species”
in virology.
,4. Who disproved spontaneous generation using swan-neck flasks?
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.
5. 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.
6. 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, some viruses) cannot be
grown on artificial media, limiting Koch’s postulates.
7. 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.
8. Which type of microscopy uses ultraviolet light to excite fluorophores?
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.
9. 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 = 400x.
10. Which of the following is present in ALL bacteria?
A. Cell wall
B. Nucleus
C. Cell membrane
D. Endospore
Correct answer: C. Cell membrane
Rationale: All bacteria have a cell membrane (plasma membrane). They lack
membrane-bound organelles. Some bacteria lack a cell wall (Mycoplasma).
11. 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 (NAG/NAM) and amino
acids, unique to bacteria.
12. 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: Gram-positive cells have multiple layers of peptidoglycan that trap the
crystal violet-iodine complex after decolorization.
13. Gram-negative bacteria appear pink because:
A. They lack a cell wall.
B. Their thin peptidoglycan cannot retain the crystal violet-iodine complex and
they take up safranin.
C. They have a thick layer of lipopolysaccharide.
D. They are stained only by the primary stain.
Correct answer: B. Their thin peptidoglycan cannot retain the crystal violet-
iodine complex and they take up safranin.
Rationale: Alcohol dissolves the outer membrane and washes out crystal violet;
safranin counterstains the now colorless cells.
14. The outer membrane of Gram-negative bacteria contains:
A. Teichoic acid
B. Lipopolysaccharide (LPS)
C. Peptidoglycan only
D. Mycolic acid
Correct answer: B. Lipopolysaccharide (LPS)
Rationale: LPS is the major component of the outer membrane and acts as an
endotoxin.
15. Which bacterial structure is responsible for attachment to surfaces and is
involved in biofilm formation?
A. Flagella
B. Pili (fimbriae)
C. Ribosomes
D. Endospores
Correct answer: B. Pili (fimbriae)
Rationale: Fimbriae are short, hair-like structures that mediate adherence to
surfaces and host cells.
