BIO 250 Exam 1 V1 | BIO 250 Microbiology | Actual Q&A with
Rationale (BIO250 Exam 1) | StraighterLine
1. Which individual is credited with being the first to observe live microorganisms, which he
described as ‘animalcules’?
A. Robert Hooke
B. Robert Koch
C. Louis Pasteur
D. Antonie van Leeuwenhoek
Correct Answer: D
Explanation: Antonie van Leeuwenhoek is widely considered the father of microbiology
because he was the first to witness live microbes through a simple microscope. He
documented his findings in letters to the Royal Society of London, detailing organisms
found in rain water and plaque. While Hooke observed cells in cork, his subjects were not
living microorganisms.
2. In the binomial system of nomenclature, which two taxonomic categories are used to name
a specific organism?
A. Family and Genus
B. Genus and Species
C. Domain and Kingdom
D. Class and Order
Correct Answer: B
Explanation: The binomial system, developed by Carolus Linnaeus, assigns every
organism a two-part scientific name. The first part represents the genus and must be
capitalized, while the second part represents the specific epithet or species. Both parts
must be italicized or underlined to follow proper scientific convention.
3. Which of the following characteristics are common to all prokaryotic cells? (Select All That
Apply)
A. Possession of a membrane-bound nucleus
B. Presence of 70S ribosomes
C. A cytoplasmic membrane
D. Genetic material located in a nucleoid region
,E. Presence of complex membrane-bound organelles like mitochondria
F. The use of DNA as the hereditary material
Correct Answer: B, C, D, F
Explanation: Prokaryotic cells are distinguished by their lack of a membrane-enclosed
nucleus and specialized organelles. They do, however, contain ribosomes for protein
synthesis, though they are smaller (70S) than eukaryotic ribosomes. All prokaryotes
possess a plasma membrane and utilize DNA to store genetic information within a nucleoid.
4. Which theory suggests that living organisms can arise from non-living matter?
A. Biogenesis
B. Cell Theory
C. Germ Theory
D. Spontaneous Generation
Correct Answer: D
Explanation: Spontaneous generation, or abiogenesis, was a long-held belief that life could
appear from inanimate objects, such as maggots appearing on rotting meat. This theory
was eventually disproved by the experiments of Francesco Redi and Louis Pasteur.
Pasteur’s swan-neck flask experiment finally demonstrated that microbes in the air were
responsible for growth in sterile broths.
5. Which type of chemical bond involves the complete transfer of electrons from one atom to
another, resulting in charged particles?
A. Covalent bond
B. Hydrogen bond
C. Ionic bond
D. Van der Waals forces
E. Polar covalent bond
Correct Answer: C
Explanation: Ionic bonds occur when an atom loses one or more electrons to another
atom, creating cations and anions. The resulting electrical attraction between the
oppositely charged ions holds the molecule together. Sodium chloride (NaCl) is a classic
example where sodium donates an electron to chlorine.
6. Which of the following is the primary component of the bacterial cell wall that provides
structural rigidity?
A. Peptidoglycan
, B. Cellulose
C. Lipopolysaccharide
D. Chitin
Correct Answer: A
Explanation: Peptidoglycan is a unique macromolecule consisting of repeating framework
of long glycan chains cross-linked by short peptide fragments. It is essential for protecting
the bacteria from osmotic pressure changes and maintaining cell shape. Most antibacterial
drugs, such as penicillin, target the synthesis of this specific layer.
7. During the Gram stain procedure, what is the role of iodine?
A. Primary stain
B. Decolorizer
C. Fixative
D. Counterstain
E. Mordant
Correct Answer: E
Explanation: Iodine acts as a mordant by forming a complex with the crystal violet dye
inside the cell wall. This CV-I complex is larger than the individual molecules and becomes
trapped within the thick peptidoglycan layer of Gram-positive bacteria. Without the
mordant, the primary stain would easily wash away during the decolorization step.
8. A bacterium that is spherical in shape and arranged in chains is described as:
A. Staphylococcus
B. Sarcina
C. Streptococcus
D. Diplococcus
Correct Answer: C
Explanation: The term ‘strepto-’ refers to a chain-like arrangement, while ‘-coccus’ refers
to a spherical shape. Therefore, Streptococcus refers to chains of spherical bacteria. In
contrast, Staphylococcus refers to grape-like clusters, and Diplococcus refers to pairs.
9. Which of the following structures is responsible for the high resistance of some bacteria to
environmental stress, including heat and chemicals?
A. Capsule
B. Endospore
Rationale (BIO250 Exam 1) | StraighterLine
1. Which individual is credited with being the first to observe live microorganisms, which he
described as ‘animalcules’?
A. Robert Hooke
B. Robert Koch
C. Louis Pasteur
D. Antonie van Leeuwenhoek
Correct Answer: D
Explanation: Antonie van Leeuwenhoek is widely considered the father of microbiology
because he was the first to witness live microbes through a simple microscope. He
documented his findings in letters to the Royal Society of London, detailing organisms
found in rain water and plaque. While Hooke observed cells in cork, his subjects were not
living microorganisms.
2. In the binomial system of nomenclature, which two taxonomic categories are used to name
a specific organism?
A. Family and Genus
B. Genus and Species
C. Domain and Kingdom
D. Class and Order
Correct Answer: B
Explanation: The binomial system, developed by Carolus Linnaeus, assigns every
organism a two-part scientific name. The first part represents the genus and must be
capitalized, while the second part represents the specific epithet or species. Both parts
must be italicized or underlined to follow proper scientific convention.
3. Which of the following characteristics are common to all prokaryotic cells? (Select All That
Apply)
A. Possession of a membrane-bound nucleus
B. Presence of 70S ribosomes
C. A cytoplasmic membrane
D. Genetic material located in a nucleoid region
,E. Presence of complex membrane-bound organelles like mitochondria
F. The use of DNA as the hereditary material
Correct Answer: B, C, D, F
Explanation: Prokaryotic cells are distinguished by their lack of a membrane-enclosed
nucleus and specialized organelles. They do, however, contain ribosomes for protein
synthesis, though they are smaller (70S) than eukaryotic ribosomes. All prokaryotes
possess a plasma membrane and utilize DNA to store genetic information within a nucleoid.
4. Which theory suggests that living organisms can arise from non-living matter?
A. Biogenesis
B. Cell Theory
C. Germ Theory
D. Spontaneous Generation
Correct Answer: D
Explanation: Spontaneous generation, or abiogenesis, was a long-held belief that life could
appear from inanimate objects, such as maggots appearing on rotting meat. This theory
was eventually disproved by the experiments of Francesco Redi and Louis Pasteur.
Pasteur’s swan-neck flask experiment finally demonstrated that microbes in the air were
responsible for growth in sterile broths.
5. Which type of chemical bond involves the complete transfer of electrons from one atom to
another, resulting in charged particles?
A. Covalent bond
B. Hydrogen bond
C. Ionic bond
D. Van der Waals forces
E. Polar covalent bond
Correct Answer: C
Explanation: Ionic bonds occur when an atom loses one or more electrons to another
atom, creating cations and anions. The resulting electrical attraction between the
oppositely charged ions holds the molecule together. Sodium chloride (NaCl) is a classic
example where sodium donates an electron to chlorine.
6. Which of the following is the primary component of the bacterial cell wall that provides
structural rigidity?
A. Peptidoglycan
, B. Cellulose
C. Lipopolysaccharide
D. Chitin
Correct Answer: A
Explanation: Peptidoglycan is a unique macromolecule consisting of repeating framework
of long glycan chains cross-linked by short peptide fragments. It is essential for protecting
the bacteria from osmotic pressure changes and maintaining cell shape. Most antibacterial
drugs, such as penicillin, target the synthesis of this specific layer.
7. During the Gram stain procedure, what is the role of iodine?
A. Primary stain
B. Decolorizer
C. Fixative
D. Counterstain
E. Mordant
Correct Answer: E
Explanation: Iodine acts as a mordant by forming a complex with the crystal violet dye
inside the cell wall. This CV-I complex is larger than the individual molecules and becomes
trapped within the thick peptidoglycan layer of Gram-positive bacteria. Without the
mordant, the primary stain would easily wash away during the decolorization step.
8. A bacterium that is spherical in shape and arranged in chains is described as:
A. Staphylococcus
B. Sarcina
C. Streptococcus
D. Diplococcus
Correct Answer: C
Explanation: The term ‘strepto-’ refers to a chain-like arrangement, while ‘-coccus’ refers
to a spherical shape. Therefore, Streptococcus refers to chains of spherical bacteria. In
contrast, Staphylococcus refers to grape-like clusters, and Diplococcus refers to pairs.
9. Which of the following structures is responsible for the high resistance of some bacteria to
environmental stress, including heat and chemicals?
A. Capsule
B. Endospore
