StraighterLine
1 TINU · 052 OIB
◆
📖 ◆
S Online College Courses — ACE CREDIT Recommended
EST. 2008
T A K E T H E N E X T S T E P I N Y O U R E D U C AT I O N
Microbiology StraighterLine Unit 1
FO U N DAT I O N S O F M I C R O B I O LO G Y: M I C R O O R GA N I S M S , C L A SS I F I C AT I O N & H I STO R I C A L D I S COV E R I E S
INSTITUTION StraighterLine PROGRAM Undergraduate — General Education Science
COURSE CODE BIO 250 COURSE TITLE Microbiology
ACADEMIC YEAR EXAM TITLE Microbiology StraighterLine Unit 1
TOTAL QUESTIONS 101 Questions FORMAT Multiple Choice — Select the Single Best Answer
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each question unless otherwise instructed.
▸ Questions cover microbial classification, cellular structure, evolutionary history, and foundational microbiologists.
▸ All taxonomy, domain classification, and historical discoveries are testable content.
▸ Correct answers and clinical/scientific rationales appear below each question for comprehensive review.
▸ All content reflects current microbiological consensus and StraighterLine Unit 1 curriculum.
SECTION I — UNIT 1: MICROORGANISMS, CLASSIFICATION & FOUNDATIONAL
Questions 1 – 101
DISCOVERIES
1. Which complex molecule contains the genetic information that makes up chromosomes and serves as the protein catalyst
for synthesis of new DNA?
A. RNA
B. DNA
C. Ribosomal protein
D. Peptidoglycan
CORRECT ANSWER B — DNA
RATIONALE DNA (deoxyribonucleic acid) is the complex molecule containing the genetic information that makes up chromosomes.
It serves as the template for its own replication, with DNA polymerase acting as the protein catalyst for synthesis of
new DNA strands. RNA is transcribed from DNA, ribosomal proteins are structural components of ribosomes, and
peptidoglycan is a bacterial cell wall polymer — none of these serve as the primary repository of hereditary
information.
,2. Genetic information from DNA encodes a sequence of nucleotides in which molecule?
A. Protein
B. Lipid
C. RNA
D. Peptidoglycan
CORRECT ANSWER C — RNA
RATIONALE Genetic information flows from DNA to RNA via transcription. The DNA sequence encodes a complementary sequence
of nucleotides in messenger RNA (mRNA), which then directs protein synthesis during translation. Proteins receive
amino acid sequence information from RNA, not nucleotide sequences. Lipids and peptidoglycan are not direct
products of genetic information transfer.
3. Which of the following best defines a microorganism?
A. Any organism larger than 1mm that is multicellular with differentiated tissues
B. Organisms too small to be seen by the naked eye, generally less than 1mm in size
C. Exclusively unicellular organisms that lack any form of genetic material
D. Only eukaryotic organisms that contain membrane-bound organelles
CORRECT ANSWER B — Organisms too small to be seen by the naked eye, generally less than 1mm in size
RATIONALE Microorganisms are defined as organisms too small to be seen by the unaided human eye, generally less than 1mm in
size. They may be unicellular or, if multicellular, lack differentiated tissues. They include prokaryotes, eukaryotes, and
acellular entities such as viruses. Option A is incorrect because microorganisms are smaller than 1mm. Option C is false
because all microorganisms contain genetic material (DNA or RNA). Option D excludes prokaryotic microorganisms
such as bacteria and archaea.
4. Which scientist is credited with discovering cells and making the first drawings of microorganisms in 1665?
A. Anton van Leeuwenhoek
B. Louis Pasteur
C. Robert Hooke
D. Robert Koch
CORRECT ANSWER C — Robert Hooke
RATIONALE Robert Hooke, in 1665, published Micrographia in which he described and illustrated cells observed in cork tissue using
a compound microscope. He was the first to use the term "cell" in a biological context. Anton van Leeuwenhoek later
made more detailed observations of living microorganisms including bacteria and protists. Pasteur disproved
spontaneous generation, and Koch established the germ theory postulates.
,5. The Kingdom Protista is characterized by which of the following descriptions?
A. Multicellular organisms with complex tissue differentiation
B. Prokaryotic cells lacking membrane-bound organelles
C. Single cell, microscopic organisms with eukaryotic cells
D. Acellular entities composed only of protein and nucleic acid
CORRECT ANSWER C — Single cell, microscopic organisms with eukaryotic cells
RATIONALE The Kingdom Protista consists of single-celled, microscopic organisms that possess eukaryotic cells — meaning they
have a true nucleus and membrane-bound organelles. This kingdom includes algae, protozoa, slime molds, and water
molds. Option A describes higher organisms (plants/animals). Option B describes bacteria and archaea (prokaryotes).
Option D describes viruses, which are acellular and not classified in any kingdom.
6. In microbiology, what defines a species?
A. A group of organisms that all have identical genomes
B. A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding
C. Any organism that can be cultured on agar media
D. Organisms that share the same ribosomal RNA sequence without any variation
CORRECT ANSWER B — A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding
RATIONALE A species is classically defined as a group of living organisms consisting of similar individuals capable of exchanging
genes or interbreeding. In microbiology, this definition is modified because bacteria reproduce asexually; therefore,
microbial species are often defined by genetic similarity (e.g., 16S rRNA gene sequence identity thresholds) and shared
phenotypic characteristics. Identical genomes are not required — natural variation exists within species. Culturability is
not a defining criterion, as many microbes are unculturable.
7. Who developed the use of agar as a solidifying agent for microbiological media?
A. Robert Koch
B. Louis Pasteur
C. Fanny Hesse
D. Joseph Lister
CORRECT ANSWER C — Fanny Hesse
RATIONALE Fanny Hesse, working in Robert Koch's laboratory, suggested using agar (derived from seaweed) as a solidifying agent
for microbiological culture media. She had learned of agar's gelling properties from its use in cooking. Agar proved
superior to gelatin because it remains solid at incubation temperatures and is not degraded by most bacteria. Koch
adopted agar for his groundbreaking work on tuberculosis and other pathogens, but the innovation is credited to
Hesse.
, 8. Viruses are composed of which two primary components?
A. Proteins and lipids
B. Carbohydrates and water
C. Nucleic acids and proteins
D. Peptidoglycan and enzymes
CORRECT ANSWER C — Nucleic acids and proteins
RATIONALE Viruses are acellular entities composed of nucleic acids (either DNA or RNA, never both) surrounded by a protective
protein coat called a capsid. Some viruses also possess a lipid envelope, but the two fundamental components are
nucleic acids and proteins. Viruses are approximately 10,000 times smaller than bacteria. Peptidoglycan is a
component of bacterial cell walls, not viral structures. Carbohydrates may be present on viral glycoproteins but are not
a defining structural component.
9. Which scientist first demonstrated that nitrogen-fixing rhizobia grow as endosymbionts within leguminous plants?
A. Sergi Winogradsky
B. Martinus Beijerinck
C. Louis Pasteur
D. Alexander Fleming
CORRECT ANSWER B — Martinus Beijerinck
RATIONALE Martinus Beijerinck first demonstrated that nitrogen-fixing rhizobia bacteria grow as endosymbionts within the root
nodules of leguminous plants, where they convert atmospheric nitrogen (N₂) into ammonia (NH₃) that the plant can
use. Winogradsky pioneered soil microbiology with work on sulfur and iron oxidation. Pasteur developed
pasteurization and vaccines. Fleming discovered penicillin.
10. What was the key property of "leaky liposomes" that made them significant in prebiotic evolution experiments conducted
by Jack Szostak?
A. They prevented all molecules from entering or exiting the vesicle
B. They allowed single RNA nucleotides to enter but prevented large RNA chains from leaving
C. They catalyzed protein synthesis autonomously
D. They contained fully formed ribosomes for translation
CORRECT ANSWER B — They allowed single RNA nucleotides to enter but prevented large RNA chains from leaving
RATIONALE Jack Szostak explored how protocells might have formed by creating liposomes with "leaky" membranes. These
membranes permitted small RNA nucleotides to diffuse into the liposome while retaining larger synthesized RNA
chains inside. This selective permeability is significant because it demonstrates how early protocells could have
accumulated genetic material, a critical step toward the development of self-replicating systems and the first true cells.
1 TINU · 052 OIB
◆
📖 ◆
S Online College Courses — ACE CREDIT Recommended
EST. 2008
T A K E T H E N E X T S T E P I N Y O U R E D U C AT I O N
Microbiology StraighterLine Unit 1
FO U N DAT I O N S O F M I C R O B I O LO G Y: M I C R O O R GA N I S M S , C L A SS I F I C AT I O N & H I STO R I C A L D I S COV E R I E S
INSTITUTION StraighterLine PROGRAM Undergraduate — General Education Science
COURSE CODE BIO 250 COURSE TITLE Microbiology
ACADEMIC YEAR EXAM TITLE Microbiology StraighterLine Unit 1
TOTAL QUESTIONS 101 Questions FORMAT Multiple Choice — Select the Single Best Answer
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each question unless otherwise instructed.
▸ Questions cover microbial classification, cellular structure, evolutionary history, and foundational microbiologists.
▸ All taxonomy, domain classification, and historical discoveries are testable content.
▸ Correct answers and clinical/scientific rationales appear below each question for comprehensive review.
▸ All content reflects current microbiological consensus and StraighterLine Unit 1 curriculum.
SECTION I — UNIT 1: MICROORGANISMS, CLASSIFICATION & FOUNDATIONAL
Questions 1 – 101
DISCOVERIES
1. Which complex molecule contains the genetic information that makes up chromosomes and serves as the protein catalyst
for synthesis of new DNA?
A. RNA
B. DNA
C. Ribosomal protein
D. Peptidoglycan
CORRECT ANSWER B — DNA
RATIONALE DNA (deoxyribonucleic acid) is the complex molecule containing the genetic information that makes up chromosomes.
It serves as the template for its own replication, with DNA polymerase acting as the protein catalyst for synthesis of
new DNA strands. RNA is transcribed from DNA, ribosomal proteins are structural components of ribosomes, and
peptidoglycan is a bacterial cell wall polymer — none of these serve as the primary repository of hereditary
information.
,2. Genetic information from DNA encodes a sequence of nucleotides in which molecule?
A. Protein
B. Lipid
C. RNA
D. Peptidoglycan
CORRECT ANSWER C — RNA
RATIONALE Genetic information flows from DNA to RNA via transcription. The DNA sequence encodes a complementary sequence
of nucleotides in messenger RNA (mRNA), which then directs protein synthesis during translation. Proteins receive
amino acid sequence information from RNA, not nucleotide sequences. Lipids and peptidoglycan are not direct
products of genetic information transfer.
3. Which of the following best defines a microorganism?
A. Any organism larger than 1mm that is multicellular with differentiated tissues
B. Organisms too small to be seen by the naked eye, generally less than 1mm in size
C. Exclusively unicellular organisms that lack any form of genetic material
D. Only eukaryotic organisms that contain membrane-bound organelles
CORRECT ANSWER B — Organisms too small to be seen by the naked eye, generally less than 1mm in size
RATIONALE Microorganisms are defined as organisms too small to be seen by the unaided human eye, generally less than 1mm in
size. They may be unicellular or, if multicellular, lack differentiated tissues. They include prokaryotes, eukaryotes, and
acellular entities such as viruses. Option A is incorrect because microorganisms are smaller than 1mm. Option C is false
because all microorganisms contain genetic material (DNA or RNA). Option D excludes prokaryotic microorganisms
such as bacteria and archaea.
4. Which scientist is credited with discovering cells and making the first drawings of microorganisms in 1665?
A. Anton van Leeuwenhoek
B. Louis Pasteur
C. Robert Hooke
D. Robert Koch
CORRECT ANSWER C — Robert Hooke
RATIONALE Robert Hooke, in 1665, published Micrographia in which he described and illustrated cells observed in cork tissue using
a compound microscope. He was the first to use the term "cell" in a biological context. Anton van Leeuwenhoek later
made more detailed observations of living microorganisms including bacteria and protists. Pasteur disproved
spontaneous generation, and Koch established the germ theory postulates.
,5. The Kingdom Protista is characterized by which of the following descriptions?
A. Multicellular organisms with complex tissue differentiation
B. Prokaryotic cells lacking membrane-bound organelles
C. Single cell, microscopic organisms with eukaryotic cells
D. Acellular entities composed only of protein and nucleic acid
CORRECT ANSWER C — Single cell, microscopic organisms with eukaryotic cells
RATIONALE The Kingdom Protista consists of single-celled, microscopic organisms that possess eukaryotic cells — meaning they
have a true nucleus and membrane-bound organelles. This kingdom includes algae, protozoa, slime molds, and water
molds. Option A describes higher organisms (plants/animals). Option B describes bacteria and archaea (prokaryotes).
Option D describes viruses, which are acellular and not classified in any kingdom.
6. In microbiology, what defines a species?
A. A group of organisms that all have identical genomes
B. A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding
C. Any organism that can be cultured on agar media
D. Organisms that share the same ribosomal RNA sequence without any variation
CORRECT ANSWER B — A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding
RATIONALE A species is classically defined as a group of living organisms consisting of similar individuals capable of exchanging
genes or interbreeding. In microbiology, this definition is modified because bacteria reproduce asexually; therefore,
microbial species are often defined by genetic similarity (e.g., 16S rRNA gene sequence identity thresholds) and shared
phenotypic characteristics. Identical genomes are not required — natural variation exists within species. Culturability is
not a defining criterion, as many microbes are unculturable.
7. Who developed the use of agar as a solidifying agent for microbiological media?
A. Robert Koch
B. Louis Pasteur
C. Fanny Hesse
D. Joseph Lister
CORRECT ANSWER C — Fanny Hesse
RATIONALE Fanny Hesse, working in Robert Koch's laboratory, suggested using agar (derived from seaweed) as a solidifying agent
for microbiological culture media. She had learned of agar's gelling properties from its use in cooking. Agar proved
superior to gelatin because it remains solid at incubation temperatures and is not degraded by most bacteria. Koch
adopted agar for his groundbreaking work on tuberculosis and other pathogens, but the innovation is credited to
Hesse.
, 8. Viruses are composed of which two primary components?
A. Proteins and lipids
B. Carbohydrates and water
C. Nucleic acids and proteins
D. Peptidoglycan and enzymes
CORRECT ANSWER C — Nucleic acids and proteins
RATIONALE Viruses are acellular entities composed of nucleic acids (either DNA or RNA, never both) surrounded by a protective
protein coat called a capsid. Some viruses also possess a lipid envelope, but the two fundamental components are
nucleic acids and proteins. Viruses are approximately 10,000 times smaller than bacteria. Peptidoglycan is a
component of bacterial cell walls, not viral structures. Carbohydrates may be present on viral glycoproteins but are not
a defining structural component.
9. Which scientist first demonstrated that nitrogen-fixing rhizobia grow as endosymbionts within leguminous plants?
A. Sergi Winogradsky
B. Martinus Beijerinck
C. Louis Pasteur
D. Alexander Fleming
CORRECT ANSWER B — Martinus Beijerinck
RATIONALE Martinus Beijerinck first demonstrated that nitrogen-fixing rhizobia bacteria grow as endosymbionts within the root
nodules of leguminous plants, where they convert atmospheric nitrogen (N₂) into ammonia (NH₃) that the plant can
use. Winogradsky pioneered soil microbiology with work on sulfur and iron oxidation. Pasteur developed
pasteurization and vaccines. Fleming discovered penicillin.
10. What was the key property of "leaky liposomes" that made them significant in prebiotic evolution experiments conducted
by Jack Szostak?
A. They prevented all molecules from entering or exiting the vesicle
B. They allowed single RNA nucleotides to enter but prevented large RNA chains from leaving
C. They catalyzed protein synthesis autonomously
D. They contained fully formed ribosomes for translation
CORRECT ANSWER B — They allowed single RNA nucleotides to enter but prevented large RNA chains from leaving
RATIONALE Jack Szostak explored how protocells might have formed by creating liposomes with "leaky" membranes. These
membranes permitted small RNA nucleotides to diffuse into the liposome while retaining larger synthesized RNA
chains inside. This selective permeability is significant because it demonstrates how early protocells could have
accumulated genetic material, a critical step toward the development of self-replicating systems and the first true cells.
