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D2.1.12 (HL)—Cell proliferation

Cell proliferation increases cell number through repeated mitosis, measurable by mitotic index in growth, regeneration and tumours in active tissues.

Syllabus
First assessment 2025
Objective
D2.1.12
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceMay 2024
Most common paperPaper2
Typical marks1–2

Common command terms

  • Distinguish
  • Deduce
  • Calculate
  • Describe
  • Compare
  • Evaluate
  • Outline
  • Identify
  • Suggest

Scoring notes

Common mistake
Using raw numbers without calculating the fraction of mitotic cells.

Recent exam appearances

May 2024Paper3 ["HL"] · TZ21(b)(ii)[ 1 ]D2.1.12 (HL)—Cell proliferation
May 2024Paper3 ["HL"] · TZ21(b)(i)[ 1 ]D2.1.12 (HL)—Cell proliferation
May 2024Paper3 ["HL"] · TZ21(a)(i)[ 2 ]D2.1.12 (HL)—Cell proliferation
May 2021Paper2 ["HL"] · TZ11(d)[ 3 ]D2.1.12 (HL)—Cell proliferation
May 2021Paper2 ["HL"] · TZ11(b)[ 3 ]D2.1.12 (HL)—Cell proliferation
Practice this objective

Coverage 2016–2024 · Updated 16 Jul 2026

Cell Proliferation Expands Cell Number

HL only

Cell proliferation is repeated passage through growth and mitosis that increases cell number for growth, routine replacement or tissue repair.

Biological need Syllabus example
Growth Repeated division in plant meristems and early animal embryos
Routine replacement New skin cells replace cells continually lost from the surface
Tissue repair Cells near a skin wound proliferate to replace damaged tissue

Proliferation increases cell number only when new cells are produced faster than cells are lost. Signals regulate which cells enter and continue through the cell cycle.

Cell growth increases the size or contents of one cell; cell proliferation increases the number of cells. Uncontrolled proliferation can disrupt tissue organization.

Cell proliferation

HL only

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Distinguish / Deduce / Calculate.

Command terms

Distinguish / Deduce / Calculate / Describe / Compare / Evaluate / Outline / Identify / Suggest

What earns marks

Build the answer around this relationship: Cell proliferation increases cell number by repeated division.

Watch for

Using raw numbers without calculating the fraction of mitotic cells.

Representative question

Question 1

[Maximum number: 3]

Based on the data, evaluate the evidence for leptin promoting regeneration of liver tissue.

HL Cell Cycle and Cancer

HL only

Cell proliferation increases cell number by repeated mitosis, as in plant meristems, early embryos, skin replacement, and wound healing. The cell cycle includes interphase, mitosis, and cytokinesis; interphase has G1 growth, S-phase DNA replication, and G2 preparation. Interphase is metabolically active, not resting; cells synthesize proteins, replicate DNA, grow cytoplasm, and increase organelles. Cyclin concentrations rise and fall to activate cyclin-dependent kinases; CDK-cyclin complexes such as MPF control checkpoints and mitosis entry. Proto-oncogene activation and tumour suppressor loss disrupt checkpoints; accumulated mutations can cause uncontrolled proliferation and cancer. Benign tumours grow locally, malignant tumours invade neighbouring tissues, and metastasis spreads cancer cells to form secondary tumours.

Concept essentials

  • Cell proliferation increases cell number by repeated division.
  • Mitotic index is cells in mitosis divided by total observed cells.
  • Meristems and regenerating tissues can have high mitotic indices.
  • Chemicals that reduce mitotic index can slow growth or proliferation.