BSC 108 Exam #3 – Questions & Solutions (100%)
Introduction to Biological Sciences – Exam #3.
Module I: Cell Division & Reproduction (Questions 1–12)
Section A: Mitosis (Q1–5)
Q1: During which phase of mitosis do sister chromatids separate and move toward opposite
poles?
• A. Prophase
• B. Metaphase
• C. Anaphase
• D. Telophase
Correct Answer: C
Rationale: Anaphase is characterized by the separation of sister chromatids, which are pulled to
opposite poles by spindle fibers attached to kinetochores. Prophase (A): chromosomes
condense. Metaphase (B): chromosomes align at the metaphase plate. Telophase (D): nuclear
envelope reforms. Common error: confusing anaphase (separation) with metaphase
(alignment).
Q2: If a diploid cell (2n = 16) undergoes mitosis, how many chromosomes will each daughter
cell contain?
• A. 8
• B. 16
• C. 32
• D. 4
Correct Answer: B
,Rationale: Mitosis produces two genetically identical daughter cells with the same chromosome
number as the parent cell (2n → 2n). If the parent cell has 16 chromosomes, each daughter cell
also has 16 chromosomes. Meiosis would produce 8 chromosomes (n = 8).
Q3: Which of the following correctly lists the phases of mitosis in order?
• A. Prophase, Metaphase, Anaphase, Telophase
• B. Metaphase, Prophase, Anaphase, Telophase
• C. Prophase, Anaphase, Metaphase, Telophase
• D. Interphase, Prophase, Metaphase, Anaphase
Correct Answer: A
Rationale: Mnemonic: PMAT. Interphase is not a phase of mitosis (it is part of the cell cycle
before mitosis). The correct sequence is Prophase → Metaphase → Anaphase → Telophase.
Q4: The G₁ checkpoint evaluates which of the following conditions?
• A. Spindle fiber attachment to kinetochores
• B. DNA replication completeness
• C. Cell size, nutrient availability, and growth factors
• D. Chromosome alignment at the metaphase plate
Correct Answer: C
Rationale: The G₁ checkpoint is the most important cell cycle checkpoint. It assesses cell size,
nutrient availability, growth factors, and DNA integrity before the cell commits to S phase. G₂
checkpoint (B) checks DNA replication completeness. M checkpoint (A, D) verifies spindle
attachment and chromosome alignment.
Q5: A mutation in the p53 tumor suppressor gene leads to uncontrolled cell division because:
• A. p53 normally promotes DNA replication
• B. p53 normally arrests the cell cycle when DNA is damaged
• C. p53 normally activates cyclin-dependent kinases
, • D. p53 normally prevents apoptosis
Correct Answer: B
Rationale: p53 is a tumor suppressor that acts as the "guardian of the genome." When DNA
damage is detected, p53 triggers cell cycle arrest (at G₁ checkpoint) to allow DNA repair or
initiates apoptosis if damage is irreparable. Mutations in p53 allow damaged cells to continue
dividing, leading to cancer.
Section B: Meiosis (Q6–10)
Q6: Crossing over occurs during which phase of meiosis?
• A. Prophase I
• B. Metaphase I
• C. Prophase II
• D. Anaphase II
Correct Answer: A
Rationale: Crossing over (exchange of genetic material between homologous chromosomes)
occurs during Prophase I when homologous chromosomes pair up (synapsis) to form tetrads.
Chiasmata are visible sites of crossing over. Crossing over does not occur in mitosis or meiosis II.
Q7: A cell with 46 chromosomes undergoes meiosis. How many chromosomes will each gamete
contain?
• A. 23
• B. 46
• C. 92
• D. 12
Correct Answer: A
Rationale: Meiosis is reductional division: diploid (2n = 46) → haploid (n = 23) gametes. Each
gamete receives one copy of each homologous chromosome. Fertilization restores the diploid
number (23 + 23 = 46).
Introduction to Biological Sciences – Exam #3.
Module I: Cell Division & Reproduction (Questions 1–12)
Section A: Mitosis (Q1–5)
Q1: During which phase of mitosis do sister chromatids separate and move toward opposite
poles?
• A. Prophase
• B. Metaphase
• C. Anaphase
• D. Telophase
Correct Answer: C
Rationale: Anaphase is characterized by the separation of sister chromatids, which are pulled to
opposite poles by spindle fibers attached to kinetochores. Prophase (A): chromosomes
condense. Metaphase (B): chromosomes align at the metaphase plate. Telophase (D): nuclear
envelope reforms. Common error: confusing anaphase (separation) with metaphase
(alignment).
Q2: If a diploid cell (2n = 16) undergoes mitosis, how many chromosomes will each daughter
cell contain?
• A. 8
• B. 16
• C. 32
• D. 4
Correct Answer: B
,Rationale: Mitosis produces two genetically identical daughter cells with the same chromosome
number as the parent cell (2n → 2n). If the parent cell has 16 chromosomes, each daughter cell
also has 16 chromosomes. Meiosis would produce 8 chromosomes (n = 8).
Q3: Which of the following correctly lists the phases of mitosis in order?
• A. Prophase, Metaphase, Anaphase, Telophase
• B. Metaphase, Prophase, Anaphase, Telophase
• C. Prophase, Anaphase, Metaphase, Telophase
• D. Interphase, Prophase, Metaphase, Anaphase
Correct Answer: A
Rationale: Mnemonic: PMAT. Interphase is not a phase of mitosis (it is part of the cell cycle
before mitosis). The correct sequence is Prophase → Metaphase → Anaphase → Telophase.
Q4: The G₁ checkpoint evaluates which of the following conditions?
• A. Spindle fiber attachment to kinetochores
• B. DNA replication completeness
• C. Cell size, nutrient availability, and growth factors
• D. Chromosome alignment at the metaphase plate
Correct Answer: C
Rationale: The G₁ checkpoint is the most important cell cycle checkpoint. It assesses cell size,
nutrient availability, growth factors, and DNA integrity before the cell commits to S phase. G₂
checkpoint (B) checks DNA replication completeness. M checkpoint (A, D) verifies spindle
attachment and chromosome alignment.
Q5: A mutation in the p53 tumor suppressor gene leads to uncontrolled cell division because:
• A. p53 normally promotes DNA replication
• B. p53 normally arrests the cell cycle when DNA is damaged
• C. p53 normally activates cyclin-dependent kinases
, • D. p53 normally prevents apoptosis
Correct Answer: B
Rationale: p53 is a tumor suppressor that acts as the "guardian of the genome." When DNA
damage is detected, p53 triggers cell cycle arrest (at G₁ checkpoint) to allow DNA repair or
initiates apoptosis if damage is irreparable. Mutations in p53 allow damaged cells to continue
dividing, leading to cancer.
Section B: Meiosis (Q6–10)
Q6: Crossing over occurs during which phase of meiosis?
• A. Prophase I
• B. Metaphase I
• C. Prophase II
• D. Anaphase II
Correct Answer: A
Rationale: Crossing over (exchange of genetic material between homologous chromosomes)
occurs during Prophase I when homologous chromosomes pair up (synapsis) to form tetrads.
Chiasmata are visible sites of crossing over. Crossing over does not occur in mitosis or meiosis II.
Q7: A cell with 46 chromosomes undergoes meiosis. How many chromosomes will each gamete
contain?
• A. 23
• B. 46
• C. 92
• D. 12
Correct Answer: A
Rationale: Meiosis is reductional division: diploid (2n = 46) → haploid (n = 23) gametes. Each
gamete receives one copy of each homologous chromosome. Fertilization restores the diploid
number (23 + 23 = 46).
