BIO 250 Exam 1 V3 | BIO 250 Microbiology
| Actual Q&A with Rationale (BIO250 Exam
1) | StraighterLine
1. Who is credited with being the first person to observe and describe live microorganisms,
which he called ‘animalcules’?
A. Antonie van Leeuwenhoek
B. Louis Pasteur
C. Robert Hooke
D. Robert Koch
Answer: A
Rationale: Antonie van Leeuwenhoek used high-quality simple lenses he ground himself to
observe single-celled organisms in water and on teeth. His detailed drawings provided the
first evidence of the microscopic world’s diversity. While Hooke observed cells in cork,
Leeuwenhoek was the first to see living motile bacteria.
2. Which scientist successfully disproved the theory of spontaneous generation using an S-
shaped flask?
A. Francesco Redi
B. Louis Pasteur
C. John Needham
,D. Lazzaro Spallanzani
Answer: B
Rationale: Louis Pasteur’s experiment demonstrated that microbes are present in the air
and do not arise from non-living matter. The S-shaped neck allowed air to enter but
trapped dust and microbes in the curve. This experiment provided the foundation for the
theory of biogenesis, which states that living cells arise only from preexisting living cells.
3. In the Gram stain procedure, what is the specific role of iodine?
A. Primary stain
B. Mordant
C. Decolorizer
D. Counterstain
Answer: B
Rationale: Iodine acts as a mordant by forming a complex with the crystal violet dye inside
the bacterial cell. This large crystal violet-iodine complex is harder to wash out of the thick
peptidoglycan layer of Gram-positive cells. Without this step, the primary stain would
easily wash away during the decolorization phase.
4. Which of the following are characteristics commonly associated with prokaryotic
organisms? (Select all that apply)
A. DNA is not enclosed within a membrane-bound nucleus
, B. Contain membrane-bound organelles such as mitochondria
C. DNA is typically a single, circular chromosome
D. Cell walls usually contain complex chitin
E. Usually divide by binary fission
F. Contain 70S ribosomes
Answer: A, C, E, F
Rationale: Prokaryotes are defined by their lack of a membrane-enclosed nucleus and
membrane-bound organelles. They typically possess a single circular chromosome and
smaller 70S ribosomes compared to the 80S ribosomes found in eukaryotes. Reproduction
occurs through binary fission, a simpler process than mitosis.
5. The primary chemically defined component of the bacterial cell wall that provides
structural rigidity is:
A. Cellulose
B. Chitin
C. Glycogen
D. Peptidoglycan
Answer: D
Rationale: Peptidoglycan consists of repeating units of NAG and NAM sugars cross-linked
by short peptides. This mesh-like layer protects the bacterium from osmotic lysis in various
| Actual Q&A with Rationale (BIO250 Exam
1) | StraighterLine
1. Who is credited with being the first person to observe and describe live microorganisms,
which he called ‘animalcules’?
A. Antonie van Leeuwenhoek
B. Louis Pasteur
C. Robert Hooke
D. Robert Koch
Answer: A
Rationale: Antonie van Leeuwenhoek used high-quality simple lenses he ground himself to
observe single-celled organisms in water and on teeth. His detailed drawings provided the
first evidence of the microscopic world’s diversity. While Hooke observed cells in cork,
Leeuwenhoek was the first to see living motile bacteria.
2. Which scientist successfully disproved the theory of spontaneous generation using an S-
shaped flask?
A. Francesco Redi
B. Louis Pasteur
C. John Needham
,D. Lazzaro Spallanzani
Answer: B
Rationale: Louis Pasteur’s experiment demonstrated that microbes are present in the air
and do not arise from non-living matter. The S-shaped neck allowed air to enter but
trapped dust and microbes in the curve. This experiment provided the foundation for the
theory of biogenesis, which states that living cells arise only from preexisting living cells.
3. In the Gram stain procedure, what is the specific role of iodine?
A. Primary stain
B. Mordant
C. Decolorizer
D. Counterstain
Answer: B
Rationale: Iodine acts as a mordant by forming a complex with the crystal violet dye inside
the bacterial cell. This large crystal violet-iodine complex is harder to wash out of the thick
peptidoglycan layer of Gram-positive cells. Without this step, the primary stain would
easily wash away during the decolorization phase.
4. Which of the following are characteristics commonly associated with prokaryotic
organisms? (Select all that apply)
A. DNA is not enclosed within a membrane-bound nucleus
, B. Contain membrane-bound organelles such as mitochondria
C. DNA is typically a single, circular chromosome
D. Cell walls usually contain complex chitin
E. Usually divide by binary fission
F. Contain 70S ribosomes
Answer: A, C, E, F
Rationale: Prokaryotes are defined by their lack of a membrane-enclosed nucleus and
membrane-bound organelles. They typically possess a single circular chromosome and
smaller 70S ribosomes compared to the 80S ribosomes found in eukaryotes. Reproduction
occurs through binary fission, a simpler process than mitosis.
5. The primary chemically defined component of the bacterial cell wall that provides
structural rigidity is:
A. Cellulose
B. Chitin
C. Glycogen
D. Peptidoglycan
Answer: D
Rationale: Peptidoglycan consists of repeating units of NAG and NAM sugars cross-linked
by short peptides. This mesh-like layer protects the bacterium from osmotic lysis in various
