BIOL 101 Exam 2 V2 | BIOL 101 Principles of Biology | Actual Q&A
with Rationale (BIOL101 Exam 2) | Liberty University
1. During which phase of the cell cycle is DNA replicated to ensure each new cell receives a
full set of genetic instructions?
A. G1 Phase
B. M Phase
C. G2 Phase
D. S Phase
Correct Answer: D
Explanation: The S phase, or synthesis phase, is the specific window during interphase
when the cell duplicates its chromosomal DNA. This process is vital because it provides the
necessary genetic material for two daughter cells. Without this replication, the resulting
cells would lack the instructions required for proper function and survival.
2. In a DNA molecule, which nitrogenous base always pairs with Cytosine?
A. Guanine
B. Thymine
C. Uracil
D. Adenine
Correct Answer: A
Explanation: According to Chargaff’s rules of base pairing, Guanine and Cytosine are
complementary and held together by three hydrogen bonds. This specific pairing maintains
the uniform width of the DNA double helix. Adenine, conversely, pairs with Thymine in
DNA or Uracil in RNA via two hydrogen bonds.
3. Which enzyme is primarily responsible for unwinding the DNA double helix during the
process of replication?
A. DNA Polymerase
B. Helicase
C. Ligase
D. RNA Polymerase
Correct Answer: B
,Explanation: Helicase acts as a molecular motor that separates the two strands of the DNA
double helix by breaking hydrogen bonds. This separation creates the replication fork
where other enzymes can access the template strands. Efficient unwinding is a prerequisite
for the accurate copying of the genome during the S phase.
4. What is the term for a physical or chemical agent that changes the genetic material of an
organism?
A. Carcinogen
B. Teratogen
C. Mutagen
D. Antigen
Correct Answer: C
Explanation: A mutagen is any substance or radiation that increases the frequency of
mutations above the natural background level. These agents can cause structural changes
to DNA, leading to altered proteins or regulatory sequences. Understanding mutagens is
crucial in fields like oncology and evolutionary biology.
5. In Mendelian genetics, what is the expected phenotypic ratio of a monohybrid cross
between two heterozygous parents?
A. 3:1
B. 1:1
C. 1:2:1
D. 9:3:3:1
Correct Answer: A
Explanation: A monohybrid cross between two heterozygotes (Aa x Aa) typically results in
three offspring expressing the dominant trait for every one expressing the recessive trait.
This ratio reflects the underlying genotypic ratio of 1:2:1 (AA:Aa:aa). Mendel utilized these
consistent ratios to formulate his Law of Segregation.
6. Which type of RNA carries the specific amino acids to the ribosome during protein
synthesis?
A. mRNA
B. rRNA
C. snRNA
D. tRNA
Correct Answer: D
, Explanation: Transfer RNA (tRNA) acts as the bridge between the mRNA sequence and the
growing polypeptide chain. Each tRNA molecule has an anticodon that matches a specific
codon and carries the corresponding amino acid. This ensures that the genetic code is
translated into the correct sequence of proteins.
7. Which phase of mitosis involves the alignment of chromosomes along the center of the
cell?
A. Metaphase
B. Prophase
C. Anaphase
D. Telophase
Correct Answer: A
Explanation: During metaphase, the spindle fibers pull the chromosomes until they are
perfectly aligned at the metaphase plate. This alignment is critical for the equal distribution
of genetic material to the daughter cells. The cell checks this alignment at a specific
checkpoint before proceeding to anaphase.
8. A sequence of three nucleotides on an mRNA molecule that codes for a specific amino acid
is called a:
A. Anticodon
B. Intron
C. Exon
D. Codon
Correct Answer: D
Explanation: A codon is the basic unit of the genetic code, consisting of three consecutive
nucleotides in mRNA. There are 64 possible codons, most of which specify one of the 20
standard amino acids. The reading frame established by the start codon determines how
these triplets are interpreted by the ribosome.
9. Which of the following describes a cell that contains two complete sets of chromosomes,
one from each parent?
A. Haploid
B. Aneuploid
C. Diploid
D. Polyploid
Correct Answer: C
with Rationale (BIOL101 Exam 2) | Liberty University
1. During which phase of the cell cycle is DNA replicated to ensure each new cell receives a
full set of genetic instructions?
A. G1 Phase
B. M Phase
C. G2 Phase
D. S Phase
Correct Answer: D
Explanation: The S phase, or synthesis phase, is the specific window during interphase
when the cell duplicates its chromosomal DNA. This process is vital because it provides the
necessary genetic material for two daughter cells. Without this replication, the resulting
cells would lack the instructions required for proper function and survival.
2. In a DNA molecule, which nitrogenous base always pairs with Cytosine?
A. Guanine
B. Thymine
C. Uracil
D. Adenine
Correct Answer: A
Explanation: According to Chargaff’s rules of base pairing, Guanine and Cytosine are
complementary and held together by three hydrogen bonds. This specific pairing maintains
the uniform width of the DNA double helix. Adenine, conversely, pairs with Thymine in
DNA or Uracil in RNA via two hydrogen bonds.
3. Which enzyme is primarily responsible for unwinding the DNA double helix during the
process of replication?
A. DNA Polymerase
B. Helicase
C. Ligase
D. RNA Polymerase
Correct Answer: B
,Explanation: Helicase acts as a molecular motor that separates the two strands of the DNA
double helix by breaking hydrogen bonds. This separation creates the replication fork
where other enzymes can access the template strands. Efficient unwinding is a prerequisite
for the accurate copying of the genome during the S phase.
4. What is the term for a physical or chemical agent that changes the genetic material of an
organism?
A. Carcinogen
B. Teratogen
C. Mutagen
D. Antigen
Correct Answer: C
Explanation: A mutagen is any substance or radiation that increases the frequency of
mutations above the natural background level. These agents can cause structural changes
to DNA, leading to altered proteins or regulatory sequences. Understanding mutagens is
crucial in fields like oncology and evolutionary biology.
5. In Mendelian genetics, what is the expected phenotypic ratio of a monohybrid cross
between two heterozygous parents?
A. 3:1
B. 1:1
C. 1:2:1
D. 9:3:3:1
Correct Answer: A
Explanation: A monohybrid cross between two heterozygotes (Aa x Aa) typically results in
three offspring expressing the dominant trait for every one expressing the recessive trait.
This ratio reflects the underlying genotypic ratio of 1:2:1 (AA:Aa:aa). Mendel utilized these
consistent ratios to formulate his Law of Segregation.
6. Which type of RNA carries the specific amino acids to the ribosome during protein
synthesis?
A. mRNA
B. rRNA
C. snRNA
D. tRNA
Correct Answer: D
, Explanation: Transfer RNA (tRNA) acts as the bridge between the mRNA sequence and the
growing polypeptide chain. Each tRNA molecule has an anticodon that matches a specific
codon and carries the corresponding amino acid. This ensures that the genetic code is
translated into the correct sequence of proteins.
7. Which phase of mitosis involves the alignment of chromosomes along the center of the
cell?
A. Metaphase
B. Prophase
C. Anaphase
D. Telophase
Correct Answer: A
Explanation: During metaphase, the spindle fibers pull the chromosomes until they are
perfectly aligned at the metaphase plate. This alignment is critical for the equal distribution
of genetic material to the daughter cells. The cell checks this alignment at a specific
checkpoint before proceeding to anaphase.
8. A sequence of three nucleotides on an mRNA molecule that codes for a specific amino acid
is called a:
A. Anticodon
B. Intron
C. Exon
D. Codon
Correct Answer: D
Explanation: A codon is the basic unit of the genetic code, consisting of three consecutive
nucleotides in mRNA. There are 64 possible codons, most of which specify one of the 20
standard amino acids. The reading frame established by the start codon determines how
these triplets are interpreted by the ribosome.
9. Which of the following describes a cell that contains two complete sets of chromosomes,
one from each parent?
A. Haploid
B. Aneuploid
C. Diploid
D. Polyploid
Correct Answer: C
