BIOL133 K006 MITOSIS LAB COMPLETE SOLUTION
2026/2027 | Spring Semester | Cell Division Lab | Pass
Guaranteed - A+ Graded
SECTION 1: CELL CYCLE PHASES - INTERPHASE & MITOTIC STAGES
(Q1-12)
Q1. During which phase of interphase does DNA replication occur, and what is the
primary enzyme responsible for this process?
A. G1 phase; DNA polymerase
B. S phase; DNA helicase
C. S phase; DNA polymerase [CORRECT]
D. G2 phase; DNA ligase
Correct Answer: C. S phase; DNA polymerase [CORRECT]
Rationale: DNA replication occurs during the S (synthesis) phase of interphase,
catalyzed primarily by DNA polymerase. Option A incorrectly places replication in G1,
which is the growth/preparation phase. Option B identifies the correct phase but the
wrong enzyme—helicase unwinds DNA but does not synthesize new strands. Option D
places replication in G2, which is actually the checkpoint and organelle duplication
phase.
Q2. A student is observing onion root tip cells under the microscope and notes that the
majority of cells show a distinct nucleus with a visible nucleolus and dispersed
chromatin. Which cell cycle phase are these cells most likely in?
,A. Prophase
B. Metaphase
C. Interphase [CORRECT]
D. Telophase
Correct Answer: C. Interphase [CORRECT]
Rationale: Interphase cells comprise approximately 90% of the cell cycle and are
characterized by a distinct nucleus, visible nucleolus, and dispersed chromatin that is
not yet condensed into visible chromosomes. Option A (prophase) shows condensed
chromosomes and nuclear envelope breakdown. Option B (metaphase) shows aligned
chromosomes at the equatorial plate. Option D (telophase) shows two reforming nuclei,
not a single intact nucleus.
Q3. During prophase of mitosis, which of the following events occurs FIRST?
A. Sister chromatids separate and move to opposite poles
B. Chromatin condenses into visible chromosomes [CORRECT]
C. Chromosomes align at the metaphase plate
D. The nuclear envelope reforms around daughter chromosomes
Correct Answer: B. Chromatin condenses into visible chromosomes [CORRECT]
Rationale: The defining first event of prophase is chromatin condensation into compact,
visible chromosomes. Option A describes anaphase. Option C describes metaphase.
Option D describes telophase. In prophase, condensation precedes nuclear envelope
breakdown and spindle formation.
Q4. A student observes a cell in which the nuclear envelope has completely broken
down, and spindle microtubules are attaching to kinetochores on the chromosomes.
The chromosomes are still somewhat scattered rather than aligned. Which mitotic
stage is the cell in?
, A. Early prophase
B. Prometaphase [CORRECT]
C. Metaphase
D. Anaphase
Correct Answer: B. Prometaphase [CORRECT]
Rationale: Prometaphase is characterized by nuclear envelope breakdown and
kinetochore microtubule attachment to chromosomes, with chromosomes still moving
toward the metaphase plate but not yet aligned. Option A (early prophase) still has an
intact nuclear envelope. Option C (metaphase) shows complete chromosome alignment
at the equatorial plate. Option D (anaphase) shows sister chromatid separation.
Q5. Which checkpoint ensures that DNA replication is complete and accurate before the
cell enters mitosis?
A. G1/S checkpoint
B. G2/M checkpoint [CORRECT]
C. Spindle assembly checkpoint
D. Metaphase-anaphase transition checkpoint
Correct Answer: B. G2/M checkpoint [CORRECT]
Rationale: The G2/M checkpoint verifies that DNA replication is complete and that any
DNA damage has been repaired before the cell commits to mitosis. Option A (G1/S)
checks cell size, nutrient availability, and DNA damage before replication begins. Option
C (spindle assembly checkpoint) ensures proper kinetochore-microtubule attachment
during metaphase. Option D is not a standard checkpoint term.
Q6. During which phase of the cell cycle does the cell double its organelle content and
synthesize proteins necessary for cell division?
A. G1 phase only
B. S phase only
2026/2027 | Spring Semester | Cell Division Lab | Pass
Guaranteed - A+ Graded
SECTION 1: CELL CYCLE PHASES - INTERPHASE & MITOTIC STAGES
(Q1-12)
Q1. During which phase of interphase does DNA replication occur, and what is the
primary enzyme responsible for this process?
A. G1 phase; DNA polymerase
B. S phase; DNA helicase
C. S phase; DNA polymerase [CORRECT]
D. G2 phase; DNA ligase
Correct Answer: C. S phase; DNA polymerase [CORRECT]
Rationale: DNA replication occurs during the S (synthesis) phase of interphase,
catalyzed primarily by DNA polymerase. Option A incorrectly places replication in G1,
which is the growth/preparation phase. Option B identifies the correct phase but the
wrong enzyme—helicase unwinds DNA but does not synthesize new strands. Option D
places replication in G2, which is actually the checkpoint and organelle duplication
phase.
Q2. A student is observing onion root tip cells under the microscope and notes that the
majority of cells show a distinct nucleus with a visible nucleolus and dispersed
chromatin. Which cell cycle phase are these cells most likely in?
,A. Prophase
B. Metaphase
C. Interphase [CORRECT]
D. Telophase
Correct Answer: C. Interphase [CORRECT]
Rationale: Interphase cells comprise approximately 90% of the cell cycle and are
characterized by a distinct nucleus, visible nucleolus, and dispersed chromatin that is
not yet condensed into visible chromosomes. Option A (prophase) shows condensed
chromosomes and nuclear envelope breakdown. Option B (metaphase) shows aligned
chromosomes at the equatorial plate. Option D (telophase) shows two reforming nuclei,
not a single intact nucleus.
Q3. During prophase of mitosis, which of the following events occurs FIRST?
A. Sister chromatids separate and move to opposite poles
B. Chromatin condenses into visible chromosomes [CORRECT]
C. Chromosomes align at the metaphase plate
D. The nuclear envelope reforms around daughter chromosomes
Correct Answer: B. Chromatin condenses into visible chromosomes [CORRECT]
Rationale: The defining first event of prophase is chromatin condensation into compact,
visible chromosomes. Option A describes anaphase. Option C describes metaphase.
Option D describes telophase. In prophase, condensation precedes nuclear envelope
breakdown and spindle formation.
Q4. A student observes a cell in which the nuclear envelope has completely broken
down, and spindle microtubules are attaching to kinetochores on the chromosomes.
The chromosomes are still somewhat scattered rather than aligned. Which mitotic
stage is the cell in?
, A. Early prophase
B. Prometaphase [CORRECT]
C. Metaphase
D. Anaphase
Correct Answer: B. Prometaphase [CORRECT]
Rationale: Prometaphase is characterized by nuclear envelope breakdown and
kinetochore microtubule attachment to chromosomes, with chromosomes still moving
toward the metaphase plate but not yet aligned. Option A (early prophase) still has an
intact nuclear envelope. Option C (metaphase) shows complete chromosome alignment
at the equatorial plate. Option D (anaphase) shows sister chromatid separation.
Q5. Which checkpoint ensures that DNA replication is complete and accurate before the
cell enters mitosis?
A. G1/S checkpoint
B. G2/M checkpoint [CORRECT]
C. Spindle assembly checkpoint
D. Metaphase-anaphase transition checkpoint
Correct Answer: B. G2/M checkpoint [CORRECT]
Rationale: The G2/M checkpoint verifies that DNA replication is complete and that any
DNA damage has been repaired before the cell commits to mitosis. Option A (G1/S)
checks cell size, nutrient availability, and DNA damage before replication begins. Option
C (spindle assembly checkpoint) ensures proper kinetochore-microtubule attachment
during metaphase. Option D is not a standard checkpoint term.
Q6. During which phase of the cell cycle does the cell double its organelle content and
synthesize proteins necessary for cell division?
A. G1 phase only
B. S phase only
