,BIOD101/BIOD 101 Module 5 Exam | Essential Biology I with
Lab | Portage Learning | Q & A | 2026/2027 Edition (PDF)
1. What is the fundamental structural unit of DNA?
A) An amino acid
B) A nucleotide
C) A monosaccharide
D) A fatty acid
Correct Answer: A nucleotide.
Rationale: DNA is a polymer made up of monomer units called nucleotides. Each nucleotide consists of a
phosphate group, a five-carbon sugar (deoxyribose), and a nitrogenous base. Amino acids are the
building blocks of proteins, monosaccharides of carbohydrates, and fatty acids of lipids.
2. Which of the following nitrogenous bases is found exclusively in DNA?
A) Adenine
B) Guanine
C) Cytosine
D) Thymine
Correct Answer: Thymine.
Rationale: Thymine is a pyrimidine base found exclusively in DNA. In RNA, thymine is replaced by uracil.
Adenine, guanine, and cytosine are found in both DNA and RNA.
3. In DNA, which base pairs with adenine?
A) Guanine
B) Cytosine
C) Thymine
,D) Uracil
Correct Answer: Thymine.
Rationale: In DNA, adenine (A) pairs with thymine (T) via two hydrogen bonds, while guanine (G) pairs
with cytosine (C) via three hydrogen bonds. This complementary base pairing is essential for DNA
structure and replication.
4. Which of the following best describes the structure of a DNA molecule?
A) A single-stranded helix
B) A double helix with antiparallel strands
C) A triple-stranded complex
D) A circular molecule found only in eukaryotes
Correct Answer: A double helix with antiparallel strands.
Rationale: DNA is structured as a double helix, with two polynucleotide strands running in opposite
(antiparallel) directions. This structure was first described by Watson and Crick.
5. What type of bond holds the two strands of a DNA double helix together?
A) Peptide bonds
B) Hydrogen bonds
C) Ionic bonds
D) Disulfide bridges
Correct Answer: Hydrogen bonds.
Rationale: Hydrogen bonds form between complementary nitrogenous bases on opposite strands—two
between A and T, and three between G and C. These bonds are weak enough to allow for DNA strand
separation during replication and transcription.
, 6. What is the primary function of DNA in a cell?
A) To catalyze chemical reactions
B) To store and transmit genetic information
C) To provide structural support
D) To transport molecules across the membrane
Correct Answer: To store and transmit genetic information.
Rationale: DNA is the hereditary material that stores the genetic instructions for the development,
functioning, growth, and reproduction of all known organisms. It transmits this information from one
generation to the next.
7. What is a gene?
A) A type of carbohydrate
B) A segment of DNA that codes for a specific protein or trait
C) A lipid molecule
D) A type of organelle
Correct Answer: A segment of DNA that codes for a specific protein or trait.
Rationale: A gene is a specific sequence of DNA nucleotides that contains the information necessary to
produce a functional product, typically a protein. Genes are the fundamental units of heredity.
8. An allele is best described as:
A) The physical location of a gene on a chromosome
B) The complete set of genes in an organism
C) A variant form of a gene
D) The observable trait of an organism
Lab | Portage Learning | Q & A | 2026/2027 Edition (PDF)
1. What is the fundamental structural unit of DNA?
A) An amino acid
B) A nucleotide
C) A monosaccharide
D) A fatty acid
Correct Answer: A nucleotide.
Rationale: DNA is a polymer made up of monomer units called nucleotides. Each nucleotide consists of a
phosphate group, a five-carbon sugar (deoxyribose), and a nitrogenous base. Amino acids are the
building blocks of proteins, monosaccharides of carbohydrates, and fatty acids of lipids.
2. Which of the following nitrogenous bases is found exclusively in DNA?
A) Adenine
B) Guanine
C) Cytosine
D) Thymine
Correct Answer: Thymine.
Rationale: Thymine is a pyrimidine base found exclusively in DNA. In RNA, thymine is replaced by uracil.
Adenine, guanine, and cytosine are found in both DNA and RNA.
3. In DNA, which base pairs with adenine?
A) Guanine
B) Cytosine
C) Thymine
,D) Uracil
Correct Answer: Thymine.
Rationale: In DNA, adenine (A) pairs with thymine (T) via two hydrogen bonds, while guanine (G) pairs
with cytosine (C) via three hydrogen bonds. This complementary base pairing is essential for DNA
structure and replication.
4. Which of the following best describes the structure of a DNA molecule?
A) A single-stranded helix
B) A double helix with antiparallel strands
C) A triple-stranded complex
D) A circular molecule found only in eukaryotes
Correct Answer: A double helix with antiparallel strands.
Rationale: DNA is structured as a double helix, with two polynucleotide strands running in opposite
(antiparallel) directions. This structure was first described by Watson and Crick.
5. What type of bond holds the two strands of a DNA double helix together?
A) Peptide bonds
B) Hydrogen bonds
C) Ionic bonds
D) Disulfide bridges
Correct Answer: Hydrogen bonds.
Rationale: Hydrogen bonds form between complementary nitrogenous bases on opposite strands—two
between A and T, and three between G and C. These bonds are weak enough to allow for DNA strand
separation during replication and transcription.
, 6. What is the primary function of DNA in a cell?
A) To catalyze chemical reactions
B) To store and transmit genetic information
C) To provide structural support
D) To transport molecules across the membrane
Correct Answer: To store and transmit genetic information.
Rationale: DNA is the hereditary material that stores the genetic instructions for the development,
functioning, growth, and reproduction of all known organisms. It transmits this information from one
generation to the next.
7. What is a gene?
A) A type of carbohydrate
B) A segment of DNA that codes for a specific protein or trait
C) A lipid molecule
D) A type of organelle
Correct Answer: A segment of DNA that codes for a specific protein or trait.
Rationale: A gene is a specific sequence of DNA nucleotides that contains the information necessary to
produce a functional product, typically a protein. Genes are the fundamental units of heredity.
8. An allele is best described as:
A) The physical location of a gene on a chromosome
B) The complete set of genes in an organism
C) A variant form of a gene
D) The observable trait of an organism
