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BSC 108 EXAM 3 (KENNEDY) PRACTICE EXAM
2026 COMPLETE (135) CURRENT TESTING
QUESTIONS AND CORRECT ANSWERS WITH
DETAILED RATIONALES.
BSC
Prepare for BSC 108 Exam 3 with this comprehensive study resource
designed to reinforce the key biology concepts covered in the course. This
document helps you review essential material, strengthen your
understanding, and identify topics that may require additional study
before the exam. Use it to improve knowledge retention and build
confidence through focused, organized preparation. An excellent
companion for efficient and successful biology exam review.
MULTIPLE CHOICE.
Section 1: DNA Structure & Composition (Questions 1–15)
1. Which of the following correctly describes the structure of a
strand of DNA?
A. A single strand of nucleotides linked by hydrogen bonds
B. A double helix resembling a twisted ladder with nucleotide
subunits
C. A triple helix with amino acid subunits
D. A branched chain of glucose molecules
Correct answer: B. A double helix resembling a twisted ladder with
nucleotide subunits
Rationale: DNA is structured as a double helix, often compared to a
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twisted ladder. The "rungs" of the ladder are formed by paired
nucleotide bases (adenine, thymine, cytosine, guanine), while the
sides are formed by covalent bonds in the sugar-phosphate
backbone.
2. What are the four nucleotide subunits found in DNA?
A. Adenine, uracil, cytosine, guanine
B. Adenine, thymine, cytosine, guanine
C. Ribose, adenine, thymine, phosphate
D. Alanine, thiamine, cysteine, glycine
Correct answer: B. Adenine, thymine, cytosine, guanine
Rationale: DNA contains four nitrogenous bases: adenine (A),
thymine (T), cytosine (C), and guanine (G). RNA uses uracil (U)
instead of thymine, which is a key distinction between the two
nucleic acids.
3. How are the nucleotide subunits held together within a DNA
strand?
A. Hydrogen bonds between sugars
B. Covalent bonds between sugar and phosphate groups
C. Ionic bonds between base pairs
D. Peptide bonds between amino acids
Correct answer: B. Covalent bonds between sugar and phosphate
groups
Rationale: Nucleotides are linked together by covalent bonds
(phosphodiester bonds) between the deoxyribose sugar of one
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nucleotide and the phosphate group of the next. The two DNA
strands are held together by hydrogen bonds between
complementary bases.
4. The sugar-phosphate backbone of DNA is composed of:
A. Deoxyribose and phosphate groups
B. Ribose and phosphate groups
C. Glucose and phosphate groups
D. Deoxyribose and nitrogenous bases
Correct answer: A. Deoxyribose and phosphate groups
Rationale: The DNA backbone is made of a sugar called
deoxyribose and a phosphate group covalently bonded to nitrogen-
containing bases.
5. What type of bond holds the two strands of DNA together?
A. Covalent bonds
B. Ionic bonds
C. Hydrogen bonds
D. Peptide bonds
Correct answer: C. Hydrogen bonds
Rationale: The nitrogen-containing bases of the two DNA strands
are held to each other by hydrogen bonds. Adenine pairs with
thymine (two hydrogen bonds) and cytosine pairs with guanine
(three hydrogen bonds).
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6. Which of the following base pairs is correct for DNA?
A. Adenine—Cytosine
B. Guanine—Thymine
C. Adenine—Thymine
D. Cytosine—Adenine
Correct answer: C. Adenine—Thymine
Rationale: In DNA, adenine (A) always pairs with thymine (T), and
cytosine (C) always pairs with guanine (G). This complementary
base pairing is essential for DNA replication and transcription.
7. How many strands does a DNA molecule contain?
A. One
B. Two
C. Three
D. Four
Correct answer: B. Two
Rationale: A DNA molecule contains two strands that are
complementary to each other. The two strands form a double helix
structure.
8. The two strands of DNA are described as:
A. Identical
B. Complementary
C. Opposite
D. Independent
BSC 108 EXAM 3 (KENNEDY) PRACTICE EXAM
2026 COMPLETE (135) CURRENT TESTING
QUESTIONS AND CORRECT ANSWERS WITH
DETAILED RATIONALES.
BSC
Prepare for BSC 108 Exam 3 with this comprehensive study resource
designed to reinforce the key biology concepts covered in the course. This
document helps you review essential material, strengthen your
understanding, and identify topics that may require additional study
before the exam. Use it to improve knowledge retention and build
confidence through focused, organized preparation. An excellent
companion for efficient and successful biology exam review.
MULTIPLE CHOICE.
Section 1: DNA Structure & Composition (Questions 1–15)
1. Which of the following correctly describes the structure of a
strand of DNA?
A. A single strand of nucleotides linked by hydrogen bonds
B. A double helix resembling a twisted ladder with nucleotide
subunits
C. A triple helix with amino acid subunits
D. A branched chain of glucose molecules
Correct answer: B. A double helix resembling a twisted ladder with
nucleotide subunits
Rationale: DNA is structured as a double helix, often compared to a
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twisted ladder. The "rungs" of the ladder are formed by paired
nucleotide bases (adenine, thymine, cytosine, guanine), while the
sides are formed by covalent bonds in the sugar-phosphate
backbone.
2. What are the four nucleotide subunits found in DNA?
A. Adenine, uracil, cytosine, guanine
B. Adenine, thymine, cytosine, guanine
C. Ribose, adenine, thymine, phosphate
D. Alanine, thiamine, cysteine, glycine
Correct answer: B. Adenine, thymine, cytosine, guanine
Rationale: DNA contains four nitrogenous bases: adenine (A),
thymine (T), cytosine (C), and guanine (G). RNA uses uracil (U)
instead of thymine, which is a key distinction between the two
nucleic acids.
3. How are the nucleotide subunits held together within a DNA
strand?
A. Hydrogen bonds between sugars
B. Covalent bonds between sugar and phosphate groups
C. Ionic bonds between base pairs
D. Peptide bonds between amino acids
Correct answer: B. Covalent bonds between sugar and phosphate
groups
Rationale: Nucleotides are linked together by covalent bonds
(phosphodiester bonds) between the deoxyribose sugar of one
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nucleotide and the phosphate group of the next. The two DNA
strands are held together by hydrogen bonds between
complementary bases.
4. The sugar-phosphate backbone of DNA is composed of:
A. Deoxyribose and phosphate groups
B. Ribose and phosphate groups
C. Glucose and phosphate groups
D. Deoxyribose and nitrogenous bases
Correct answer: A. Deoxyribose and phosphate groups
Rationale: The DNA backbone is made of a sugar called
deoxyribose and a phosphate group covalently bonded to nitrogen-
containing bases.
5. What type of bond holds the two strands of DNA together?
A. Covalent bonds
B. Ionic bonds
C. Hydrogen bonds
D. Peptide bonds
Correct answer: C. Hydrogen bonds
Rationale: The nitrogen-containing bases of the two DNA strands
are held to each other by hydrogen bonds. Adenine pairs with
thymine (two hydrogen bonds) and cytosine pairs with guanine
(three hydrogen bonds).
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6. Which of the following base pairs is correct for DNA?
A. Adenine—Cytosine
B. Guanine—Thymine
C. Adenine—Thymine
D. Cytosine—Adenine
Correct answer: C. Adenine—Thymine
Rationale: In DNA, adenine (A) always pairs with thymine (T), and
cytosine (C) always pairs with guanine (G). This complementary
base pairing is essential for DNA replication and transcription.
7. How many strands does a DNA molecule contain?
A. One
B. Two
C. Three
D. Four
Correct answer: B. Two
Rationale: A DNA molecule contains two strands that are
complementary to each other. The two strands form a double helix
structure.
8. The two strands of DNA are described as:
A. Identical
B. Complementary
C. Opposite
D. Independent
