BIOL133 K006 MITOSIS LAB ACTUAL 2026/2027 | Spring
Complete Solution with Laboratory Assessment and Detailed
Rationales | Cell Biology | Pass Guaranteed - A+ Graded
Note: This examination aligns with undergraduate biology curriculum standards for cellular
biology laboratory courses, emphasizing practical microscopy skills, mitotic stage
identification, and quantitative analysis of cell division.
Domain 1: Cell Cycle Phases (10 Questions)
Q1: In an onion root tip preparation, which region contains the highest density of actively
dividing cells?
A. Root cap - protective cells at the very tip
B. Region of cell elongation - cells increasing in size
C. Region of cell division (meristem) - approximately 1-2 mm behind the root cap
[CORRECT]
D. Root hair zone - cells specialized for absorption
Correct Answer: C
Rationale: The region of cell division (meristematic zone) contains the highest density
of actively dividing cells . This zone is located just behind the root cap and is
characterized by small, densely packed cells with large nuclei. The root cap (A) contains
protective cells that are not actively dividing. The region of cell elongation (B) shows
,cells increasing in size but not dividing. The root hair zone (D) contains differentiated
cells specialized for water absorption. For mitosis labs, root tips are cut 5-8 mm from
the tip to capture this meristematic region .
Q2: [Select-All-That-Apply] Which events occur during the S phase of interphase?
A. Cell growth and organelle duplication
B. DNA replication and chromosome duplication [CORRECT]
C. Synthesis of histone proteins
D. Sister chromatid separation
E. Preparation for mitosis (spindle protein synthesis)
Correct Answer: B, C
Rationale: The S (synthesis) phase is specifically characterized by DNA replication,
resulting in duplicated chromosomes (sister chromatids), and synthesis of histone
proteins to package the new DNA . Cell growth and organelle duplication (A) occur
primarily during G1 and G2 phases. Sister chromatid separation (D) occurs during
anaphase of mitosis, not interphase. Spindle protein synthesis (E) occurs during G2
phase. Understanding the specific events of each cell cycle phase is essential for
interpreting root tip cell observations.
Q3: A student observes an onion root tip cell with a visible nuclear envelope, dispersed
chromatin, and a clearly defined nucleolus. The cell appears metabolically active but
shows no signs of chromosome condensation. Which phase is this cell most likely in?
A. Early prophase
,B. G1 phase of interphase [CORRECT]
C. Metaphase
D. Cytokinesis
Correct Answer: B
Rationale: The presence of an intact nuclear envelope, dispersed chromatin (not
condensed chromosomes), and a visible nucleolus indicates an interphase cell . Since
the cell appears metabolically active but has not yet replicated DNA (no sister
chromatids visible), it is most likely in G1 phase. Early prophase (A) would show
beginning chromosome condensation and nuclear envelope breakdown. Metaphase (C)
shows condensed chromosomes aligned at the equator with no nuclear envelope.
Cytokinesis (D) shows cell plate formation or cleavage furrow, not intact nuclei.
Q4: [Scenario] During a mitosis lab, a student counts 200 cells in an onion root tip
squash. Of these, 160 cells show no visible chromosomes and have intact nuclear
membranes, while 40 cells show various stages of chromosome condensation and
nuclear envelope breakdown. What percentage of time do onion root tip cells spend in
interphase, based on this sample?
A. 20%
B. 40%
C. 80% [CORRECT]
D. 160%
Correct Answer: C
, Rationale: The percentage of cells in each phase approximates the percentage of time
spent in that phase . Cells without visible chromosomes and with intact nuclear
membranes are in interphase (160/200 = 0.80 or 80%). Cells with visible chromosomes
(40/200 = 20%) are in various stages of mitosis. This aligns with the biological reality
that cells spend approximately 90% of the cell cycle in interphase . Option D (160%) is
mathematically impossible. This calculation demonstrates the relationship between cell
population data and cell cycle timing.
Q5: Which checkpoint ensures that DNA replication is complete and accurate before the
cell enters mitosis?
A. G1 checkpoint - assesses cell size and nutrient availability
B. G2 checkpoint - verifies DNA replication completion and damage repair [CORRECT]
C. Metaphase checkpoint - ensures proper chromosome alignment
D. Spindle assembly checkpoint - monitors kinetochore attachment
Correct Answer: B
Rationale: The G2 checkpoint verifies that DNA replication is complete and checks for
DNA damage before the cell commits to mitosis . The G1 checkpoint (A) determines
whether the cell will enter S phase. The metaphase checkpoint (C) and spindle
assembly checkpoint (D) operate during mitosis to ensure proper chromosome
attachment and alignment, not DNA replication integrity. Understanding these regulatory
points is crucial for interpreting why some cells arrest in specific phases and for
understanding cancer biology where checkpoints fail.
Complete Solution with Laboratory Assessment and Detailed
Rationales | Cell Biology | Pass Guaranteed - A+ Graded
Note: This examination aligns with undergraduate biology curriculum standards for cellular
biology laboratory courses, emphasizing practical microscopy skills, mitotic stage
identification, and quantitative analysis of cell division.
Domain 1: Cell Cycle Phases (10 Questions)
Q1: In an onion root tip preparation, which region contains the highest density of actively
dividing cells?
A. Root cap - protective cells at the very tip
B. Region of cell elongation - cells increasing in size
C. Region of cell division (meristem) - approximately 1-2 mm behind the root cap
[CORRECT]
D. Root hair zone - cells specialized for absorption
Correct Answer: C
Rationale: The region of cell division (meristematic zone) contains the highest density
of actively dividing cells . This zone is located just behind the root cap and is
characterized by small, densely packed cells with large nuclei. The root cap (A) contains
protective cells that are not actively dividing. The region of cell elongation (B) shows
,cells increasing in size but not dividing. The root hair zone (D) contains differentiated
cells specialized for water absorption. For mitosis labs, root tips are cut 5-8 mm from
the tip to capture this meristematic region .
Q2: [Select-All-That-Apply] Which events occur during the S phase of interphase?
A. Cell growth and organelle duplication
B. DNA replication and chromosome duplication [CORRECT]
C. Synthesis of histone proteins
D. Sister chromatid separation
E. Preparation for mitosis (spindle protein synthesis)
Correct Answer: B, C
Rationale: The S (synthesis) phase is specifically characterized by DNA replication,
resulting in duplicated chromosomes (sister chromatids), and synthesis of histone
proteins to package the new DNA . Cell growth and organelle duplication (A) occur
primarily during G1 and G2 phases. Sister chromatid separation (D) occurs during
anaphase of mitosis, not interphase. Spindle protein synthesis (E) occurs during G2
phase. Understanding the specific events of each cell cycle phase is essential for
interpreting root tip cell observations.
Q3: A student observes an onion root tip cell with a visible nuclear envelope, dispersed
chromatin, and a clearly defined nucleolus. The cell appears metabolically active but
shows no signs of chromosome condensation. Which phase is this cell most likely in?
A. Early prophase
,B. G1 phase of interphase [CORRECT]
C. Metaphase
D. Cytokinesis
Correct Answer: B
Rationale: The presence of an intact nuclear envelope, dispersed chromatin (not
condensed chromosomes), and a visible nucleolus indicates an interphase cell . Since
the cell appears metabolically active but has not yet replicated DNA (no sister
chromatids visible), it is most likely in G1 phase. Early prophase (A) would show
beginning chromosome condensation and nuclear envelope breakdown. Metaphase (C)
shows condensed chromosomes aligned at the equator with no nuclear envelope.
Cytokinesis (D) shows cell plate formation or cleavage furrow, not intact nuclei.
Q4: [Scenario] During a mitosis lab, a student counts 200 cells in an onion root tip
squash. Of these, 160 cells show no visible chromosomes and have intact nuclear
membranes, while 40 cells show various stages of chromosome condensation and
nuclear envelope breakdown. What percentage of time do onion root tip cells spend in
interphase, based on this sample?
A. 20%
B. 40%
C. 80% [CORRECT]
D. 160%
Correct Answer: C
, Rationale: The percentage of cells in each phase approximates the percentage of time
spent in that phase . Cells without visible chromosomes and with intact nuclear
membranes are in interphase (160/200 = 0.80 or 80%). Cells with visible chromosomes
(40/200 = 20%) are in various stages of mitosis. This aligns with the biological reality
that cells spend approximately 90% of the cell cycle in interphase . Option D (160%) is
mathematically impossible. This calculation demonstrates the relationship between cell
population data and cell cycle timing.
Q5: Which checkpoint ensures that DNA replication is complete and accurate before the
cell enters mitosis?
A. G1 checkpoint - assesses cell size and nutrient availability
B. G2 checkpoint - verifies DNA replication completion and damage repair [CORRECT]
C. Metaphase checkpoint - ensures proper chromosome alignment
D. Spindle assembly checkpoint - monitors kinetochore attachment
Correct Answer: B
Rationale: The G2 checkpoint verifies that DNA replication is complete and checks for
DNA damage before the cell commits to mitosis . The G1 checkpoint (A) determines
whether the cell will enter S phase. The metaphase checkpoint (C) and spindle
assembly checkpoint (D) operate during mitosis to ensure proper chromosome
attachment and alignment, not DNA replication integrity. Understanding these regulatory
points is crucial for interpreting why some cells arrest in specific phases and for
understanding cancer biology where checkpoints fail.
