BIO 201 Microbiology Midterm Exam:
The Ultimate -Question
Question&Answers Review with
Rationales
1. Who is credited with first observing and describing microorganisms,
which he called "animalcules," using a simple microscope?
A. Robert Hooke
B. Antonie van Leeuwenhoek
C. Louis Pasteur
D. Robert Koch
Answer: B
Rationale: Antonie van Leeuwenhoek was a Dutch scientist who crafted
powerful single-lens microscopes and was the first to observe bacteria and
protozoa. Robert Hooke first described cells, but from a cork tree. Pasteur
and Koch are known for their work on germ theory and disease.
2. The theory of spontaneous generation, which posits that life arises
from non-living matter, was definitively disproved by which scientist?
A. John Tyndall
B. Louis Pasteur
C. Robert Koch
D. Francesco Redi
Answer: B
Rationale: Louis Pasteur's famous swan-neck flask experiment
demonstrated that sterile broth remained sterile unless exposed to dust
,and microbes from the air, thus disproving spontaneous generation. Redi
disproved it for maggots, but Pasteur's work was more definitive for
microbes.
3. What is the resolution limit of a standard compound light
microscope using visible light?
A. 0.2 nm
B. 0.2 µm
C. 2.0 µm
D. 2.0 nm
Answer: B
Rationale: The resolution of a light microscope is approximately 0.2
micrometers (µm), limited by the wavelength of visible light. This allows for
the visualization of bacteria but not viruses or internal cellular details at the
molecular level.
4. Which type of microscopy uses a beam of electrons to illuminate the
specimen, providing much higher resolution than a light microscope?
A. Fluorescence microscopy
B. Phase-contrast microscopy
C. Electron microscopy
D. Dark-field microscopy
Answer: C
Rationale: Electron microscopes use electrons, which have a much shorter
wavelength than visible light, allowing for a resolution of about 0.1 nm. This
is essential for visualizing viruses and the internal ultrastructure of cells.
5. What is the primary purpose of using an oil immersion objective
lens (100x)?
A. To prevent the slide from drying out
B. To increase the numerical aperture and resolution
C. To stain the specimen
,D. To cool the lens
Answer: B
Rationale: Oil immersion oil has the same refractive index as glass. Using it
prevents light from bending as it passes from the glass slide through the air
into the lens. This increases the numerical aperture, allowing for the capture
of more light and significantly improving resolution.
6. Which staining technique is used to differentiate bacteria based on
differences in their cell wall structure?
A. Gram stain
B. Acid-fast stain
C. Capsule stain
D. Endospore stain
Answer: A
Rationale: The Gram stain is a differential stain. It differentiates bacteria
into Gram-positive (thick peptidoglycan layer) and Gram-negative (thin
peptidoglycan and outer membrane) based on their ability to retain the
crystal violet-iodine complex.
7. In the Gram staining procedure, what is the role of the mordant,
iodine?
A. To decolorize the cells
B. To add a primary color to the cells
C. To form a crystal violet-iodine complex that is insoluble in water
D. To counterstain the cells
Answer: C
Rationale: Iodine acts as a mordant, forming a large, insoluble crystal
violet-iodine (CV-I) complex within the cell. This complex is trapped in
Gram-positive cells due to their thick peptidoglycan but is easily washed
out of Gram-negative cells during the decolorization step.
, 8. A microbiologist is examining a specimen and suspects it contains
bacteria with mycolic acid in their cell walls. Which stain should they
use?
A. Simple stain
B. Gram stain
C. Acid-fast stain
D. Negative stain
Answer: C
Rationale: The acid-fast stain is used for bacteria like Mycobacterium, which
have waxy mycolic acids in their cell walls. This lipid layer resists standard
staining and requires heating with carbolfuchsin to penetrate the cell.
9. Which type of microscopy uses fluorescent dyes to illuminate
specific structures within a cell?
A. Bright-field microscopy
B. Dark-field microscopy
C. Fluorescence microscopy
D. Transmission electron microscopy
Answer: C
Rationale: Fluorescence microscopy uses fluorochromes (fluorescent dyes)
that absorb light at one wavelength and emit it at a longer wavelength. This
can be used to tag specific antibodies or cellular structures, making them
visible against a dark background.
10. Robert Koch established a set of postulates to prove that a specific
microorganism causes a specific disease. What is the FIRST step in
these postulates?
A. Re-isolate the microorganism from the diseased host.
B. Introduce the microorganism into a healthy host.
C. Observe the microorganism in a diseased host and not in a healthy one.
D. Cultivate the microorganism in pure culture.
The Ultimate -Question
Question&Answers Review with
Rationales
1. Who is credited with first observing and describing microorganisms,
which he called "animalcules," using a simple microscope?
A. Robert Hooke
B. Antonie van Leeuwenhoek
C. Louis Pasteur
D. Robert Koch
Answer: B
Rationale: Antonie van Leeuwenhoek was a Dutch scientist who crafted
powerful single-lens microscopes and was the first to observe bacteria and
protozoa. Robert Hooke first described cells, but from a cork tree. Pasteur
and Koch are known for their work on germ theory and disease.
2. The theory of spontaneous generation, which posits that life arises
from non-living matter, was definitively disproved by which scientist?
A. John Tyndall
B. Louis Pasteur
C. Robert Koch
D. Francesco Redi
Answer: B
Rationale: Louis Pasteur's famous swan-neck flask experiment
demonstrated that sterile broth remained sterile unless exposed to dust
,and microbes from the air, thus disproving spontaneous generation. Redi
disproved it for maggots, but Pasteur's work was more definitive for
microbes.
3. What is the resolution limit of a standard compound light
microscope using visible light?
A. 0.2 nm
B. 0.2 µm
C. 2.0 µm
D. 2.0 nm
Answer: B
Rationale: The resolution of a light microscope is approximately 0.2
micrometers (µm), limited by the wavelength of visible light. This allows for
the visualization of bacteria but not viruses or internal cellular details at the
molecular level.
4. Which type of microscopy uses a beam of electrons to illuminate the
specimen, providing much higher resolution than a light microscope?
A. Fluorescence microscopy
B. Phase-contrast microscopy
C. Electron microscopy
D. Dark-field microscopy
Answer: C
Rationale: Electron microscopes use electrons, which have a much shorter
wavelength than visible light, allowing for a resolution of about 0.1 nm. This
is essential for visualizing viruses and the internal ultrastructure of cells.
5. What is the primary purpose of using an oil immersion objective
lens (100x)?
A. To prevent the slide from drying out
B. To increase the numerical aperture and resolution
C. To stain the specimen
,D. To cool the lens
Answer: B
Rationale: Oil immersion oil has the same refractive index as glass. Using it
prevents light from bending as it passes from the glass slide through the air
into the lens. This increases the numerical aperture, allowing for the capture
of more light and significantly improving resolution.
6. Which staining technique is used to differentiate bacteria based on
differences in their cell wall structure?
A. Gram stain
B. Acid-fast stain
C. Capsule stain
D. Endospore stain
Answer: A
Rationale: The Gram stain is a differential stain. It differentiates bacteria
into Gram-positive (thick peptidoglycan layer) and Gram-negative (thin
peptidoglycan and outer membrane) based on their ability to retain the
crystal violet-iodine complex.
7. In the Gram staining procedure, what is the role of the mordant,
iodine?
A. To decolorize the cells
B. To add a primary color to the cells
C. To form a crystal violet-iodine complex that is insoluble in water
D. To counterstain the cells
Answer: C
Rationale: Iodine acts as a mordant, forming a large, insoluble crystal
violet-iodine (CV-I) complex within the cell. This complex is trapped in
Gram-positive cells due to their thick peptidoglycan but is easily washed
out of Gram-negative cells during the decolorization step.
, 8. A microbiologist is examining a specimen and suspects it contains
bacteria with mycolic acid in their cell walls. Which stain should they
use?
A. Simple stain
B. Gram stain
C. Acid-fast stain
D. Negative stain
Answer: C
Rationale: The acid-fast stain is used for bacteria like Mycobacterium, which
have waxy mycolic acids in their cell walls. This lipid layer resists standard
staining and requires heating with carbolfuchsin to penetrate the cell.
9. Which type of microscopy uses fluorescent dyes to illuminate
specific structures within a cell?
A. Bright-field microscopy
B. Dark-field microscopy
C. Fluorescence microscopy
D. Transmission electron microscopy
Answer: C
Rationale: Fluorescence microscopy uses fluorochromes (fluorescent dyes)
that absorb light at one wavelength and emit it at a longer wavelength. This
can be used to tag specific antibodies or cellular structures, making them
visible against a dark background.
10. Robert Koch established a set of postulates to prove that a specific
microorganism causes a specific disease. What is the FIRST step in
these postulates?
A. Re-isolate the microorganism from the diseased host.
B. Introduce the microorganism into a healthy host.
C. Observe the microorganism in a diseased host and not in a healthy one.
D. Cultivate the microorganism in pure culture.
