IB Biology HL D2.1 Cell and nuclear division Questions

Practise IB Biology HL D2.1 by identifying cell-division stages, explaining meiosis outcomes and interpreting chromosome evidence.

154 questions in this syllabus scope, with question parts counted together.

Exam analysis

HL · 2010–2025

Papers with this topic53 / 117in the analysed sample

Latest appearanceNovember 2025

Tagged question parts86

Paper types5

Most tested objectives

D2.1.11—Meiosis generates variation18 papers
D2.1.9—Meiosis as reduction division14 papers
D2.1.10—Down syndrome6 papers
D2.1.8—Identification of mitosis phases5 papers
D2.1.12 (HL)—Cell proliferation5 papers

Common question formats

Definition or recall
Process explanation
Diagram interpretation
Calculation
Data analysis
Comparison

Recent exam appearances

November 2025Paper 1A HL · TZ3Q19[ 1 ]

November 2025Paper 1A HL · TZ1Q19[ 1 ]

May 2025Paper 2 HL · TZ3Q8(b)[ 7 ]

117 papers analysed · Tagging incomplete

Exam points

explain how mitosis generates new cells and maintains chromosome number in growth or asexual reproduction
compare animal cleavage furrows with plant cell plates and organelle distribution during cytokinesis
explain DNA replication in S phase and calculate chromatid number after replication
identify shared mitosis/meiosis chromosome events, including sister-chromatid separation
sequence and identify mitotic phases from chromosome, spindle, nuclear and micrograph evidence
calculate mitotic index from cell counts and interpret changes in meristems or inhibitor data
sequence G1, S, G2, mitosis and cytokinesis; relate interphase to growth, replication and organelle duplication
link changing cyclin levels and CDK activation to cell-cycle checkpoints, transitions and spindle progression
trace meiosis I/II from homologous- to sister-chromatid separation and identify haploid outcomes
diagnose meiotic non-disjunction from chromosome counts or karyotypes for aneuploidy
explain gamete variation through crossing over, independent assortment and fertilisation
link proto-oncogene activation or tumour-suppressor loss to checkpoint failure and tumour growth
identify metastasis when cancer cells form a secondary tumour in a distant organ

Covered syllabus points

D2.1.1—Generation of new cells D2.1.2—Cytokinesis D2.1.3—Equal and unequal cytokinesis D2.1.4—Roles of mitosis and meiosis D2.1.5—DNA replication prerequisite D2.1.6—Shared features D2.1.7—Phases of mitosis D2.1.8—Identification of mitosis phases D2.1.9—Meiosis as reduction division D2.1.10—Down syndrome D2.1.11—Meiosis generates variation D2.1.12 (HL)—Cell proliferation D2.1.13 (HL)—Cell cycle phases D2.1.14 (HL)—Cell growth during interphase D2.1.15 (HL)—Cell cycle control by cyclins D2.1.16 (HL)—Mutations in cell cycle genes D2.1.17 (HL)—Tumour differences

Exam points

Identify mitosis as the nuclear-division process by which stem cells produce new cells.

[Maximum number: 1]

What describes nuclear division in stem cells?

Clonal selection

Mitosis

Cytokinesis

Meiosis

Exam points

Compare animal and plant cytokinesis: an actin–myosin contractile ring pulls in the animal-cell membrane, while vesicles form the plant-cell plate.

[Maximum number: 1]

The micrograph shows cells in an onion root (Allium cepa) undergoing mitosis.

What is happening at X ?

Unequal cytokinesis by budding

Assembly of cell membrane and cell wall by vesicles

Contraction of a ring of actin and myosin proteins

Movement of chromosomes by microtubules

Exam points

Explain how mitosis maintains chromosome number during growth or asexual reproduction.
Identify separation of sister chromatids as an event shared by mitosis and meiosis.

[Maximum number: 7]

Members of a species typically all have the same number of chromosomes.

Describe the events in interphase and mitosis that ensure that the chromosome number does not change during an asexual life cycle.

Exam points

Identify S phase of interphase as the stage when DNA replication occurs.
Calculate chromatid number after DNA replication from the diploid chromosome number.

[Maximum number: 1]

When does DNA replication occur?

S phase of interphase

Early prophase

G phase of interphase

Late prophase

Exam points

Identify chromatid separation as an event common to both mitosis and meiosis.
Identify anaphase microtubule movement of chromatids as a shared feature of both divisions.

[Maximum number: 1]

Which statement applies to meiosis and mitosis?

Meiosis occurs in a greater number of locations in the body compared to mitosis.

Separation of chromatids occurs in both meiosis and mitosis.

Recombination occurs in both meiosis and mitosis.

Reduction in chromosome number occurs in both meiosis and mitosis.

Exam points

Sequence mitotic phases and link prophase condensation, metaphase alignment, anaphase chromatid separation and telophase nuclear reformation.
Order chromosome supercoiling, spindle attachment to centromeres and sister-chromatid movement to opposite poles.

[Maximum number: 2]

The onion (Allium cepa) root cells shown in the micrograph are in different stages of mitosis.

Identify, with a reason, the stage shown at X .

Exam points

Identify a mitosis phase from chromosome position, chromatid movement or nuclear cues in a micrograph.
Count the cells in a named mitotic phase across a micrograph.

[Maximum number: 1]

Identify the stage of mitosis labelled X in the image, giving a reason.

Exam points

Explain how one round of DNA replication is followed by two nuclear divisions, reducing chromosome number to produce haploid nuclei.
Distinguish meiosis I from meiosis II: homologous chromosomes separate in meiosis I, while sister chromatids separate in meiosis II.

[Maximum number: 1]

In which order do the following steps occur in a cell that divides by meiosis?

1 Separation of homologous chromosomes
2 DNA replication
3 Crossing over
4 Pairing of homologous chromosomes

$2 \rightarrow 4 \rightarrow 3 \rightarrow 1$

$2 \rightarrow 3 \rightarrow 4 \rightarrow 1$

$4 \rightarrow 3 \rightarrow 2 \rightarrow 1$

$4 \rightarrow 2 \rightarrow 3 \rightarrow 1$

Exam points

Identify meiosis I non-disjunction as failure of homologous chromosomes to separate, or meiosis II non-disjunction as failure of sister chromatids to separate.
Explain how a gamete with an extra chromosome 21 can lead to trisomy 21 and Down syndrome after fertilization.

[Maximum number: 4]

Reproduction depends on numerous factors both genetic and hormonal.

Describe how non-disjunction can cause Down syndrome.

Exam points

Describe how crossing over at chiasmata exchanges DNA between non-sister chromatids of homologous chromosomes.
Explain how crossing over, random bivalent orientation and fertilization create new allele combinations.

[Maximum number: 1]

The image shows details of a cell from a male locust Schistocerca gregaria.

What can be deduced from this image?

It is in prophase of mitosis.

It is in prophase II of meiosis.

It contains circular chromosomes.

It contains chiasmata as crossing over is taking place.

Exam points

Calculate mitotic index or the number of cells undergoing mitosis from cell counts and table data.
Interpret how changes in mitotic index reflect cell proliferation, including changes across extract concentrations.
Relate meristems and repeated mitosis to the continued production of plant roots, leaves and stems.

[Maximum number: 8]

Mitosis in cancerous tissues is uncontrolled and the number of cells undergoing mitosis increases exponentially. Rapidly dividing cells in root tips can be used as a model for studying the effects of anticancer drugs. Aqueous extracts of the fruit of avocado (Persea americana) and the leaves of crepe jasmine (Tabernaemontana divaricata) have been shown to be toxic to some human cancer cell lines. Root tips of the broad bean (Vicia faba) were exposed to these aqueous plant extracts over a range of concentrations.

The mitotic index is the percentage of cells examined undergoing mitosis. The table shows the numbers of broad bean root cells examined and the mitotic indices over a range of plant extract concentrations.

(a)

Calculate the number of cells undergoing mitosis using 100 ppm of crepe jasmine extract.

[ 1 ]

(b)

Describe the effect of avocado extract on mitotic index.

[ 1 ]

(c)

Compare and contrast the effect of increasing extract concentration on the mitotic indices for the two plant extracts.

[ 3 ]

(d)

Using both the table of mitotic indices and the bar charts, deduce whether these extracts contain chemicals that block mitosis in broad bean root tips.

[ 3 ]

Exam points

Outline the order of interphase, mitosis and cytokinesis, including the four mitotic phases.
Describe G1 growth, S-phase DNA replication and G2 preparation before mitosis.
Recognize interphase as the longest part of the cell cycle and describe its activity.

[Maximum number: 4]

Cells go through a repeating cycle of events in growth regions such as plant root tips and animal embryos. Outline this cell cycle.

Exam points

Identify DNA replication, transcription/protein synthesis, cell growth and organelle duplication as interphase processes.
Distinguish metabolically active interphase from mitosis by the presence of synthesis and growth rather than chromosome alignment or chromatid separation.

[Maximum number: 1]

Which of the following processes take place during interphase in animal cells?

I. Spindle formation
II. Transcription and translation
III. Increase in numbers of mitochondria

I only

I and II only

II and III only

I, II and III

Exam points

Explain how changing cyclin concentrations activate cyclin-dependent kinases and regulate cell-cycle stages.
Identify how cyclin concentrations rise and fall across interphase and mitosis to time cell-cycle transitions.

[Maximum number: 1]

The concentrations of cyclins rise and fall in cells at certain times.

What times are these?

Day and night

Seasons of the year

Stages of mitosis and interphase

Developmental stages in the life cycle

Exam points

Explain how mutations activating proto-oncogenes can alter cell-cycle regulation and contribute to uncontrolled cell division.
Relate accumulated mutations and uncontrolled cell division to tumour formation.

[Maximum number: 1]

Which characteristic is shared by all tumours?

Cells metastasize from the primary tumour

They result from mutations

Spherical in shape

Malignancy

Exam points

Identify metastasis from evidence that cancer cells from one tissue form a tumour in a different organ.
Recognize metastasis, mitosis and cytokinesis as processes involved in forming secondary tumours.

[Maximum number: 1]

What would show that a person has developed metastatic cancer?

Alveolus cells forming a tumour in the lungs

Cancer cells producing the skin pigment melanin in the liver

A tumour in the prostate gland increasing levels of prostate-specific antigen

Cancerous lymphocytes in blood plasma

a	Down's syndrome is due to an extra chromosome (21) / trisomy 21;
b	occurs in meiosis;
c	during anaphase (I or II);
d	homologous chromosomes (21) fail to separate (in anaphase I) OR chromatids (21) fail to separate (in anaphase II);
e	leads to a gamete/zygote with one extra chromosome (21);
f	(mainly) occurs in ovaries;
g	in the formation of egg cells/ova/gametes;
h	probability of nondisjunction increases with paternal/maternal age;

Exam analysis

Most tested objectives

Common question formats

Recent exam appearances

Covered syllabus points

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