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D2.1.3—Equal and unequal cytokinesis

Cytokinesis is usually equal, but budding and oogenesis can distribute cytoplasm unequally between daughter cells in specific reproductive contexts and development.

Syllabus
First assessment 2025
Objective
D2.1.3
Level
HL

Cytokinesis Can Partition Cell Contents Unequally

Cytokinesis may distribute cytoplasm and organelles equally or unequally, depending on the developmental job of the daughter cells.

Equal division supports two similar cells; unequal division gives one daughter more cytoplasm, organelles or determinants, allowing different fates after division.

Compare daughters by checking: size; organelle content; inherited determinants; later function.

An early embryo can divide asymmetrically so one daughter retains more factors that maintain stem-cell properties.

Unequal size does not automatically mean unequal DNA; nuclear division can still distribute chromosomes accurately.

Equal and unequal cytokinesis

Assessment in practice

1 marks
How it is assessed

This objective is assessed through multiple choice, commonly using Identify.

Command terms

Identify

What earns marks

Build the answer around this relationship: Equal cytokinesis gives daughter cells similar cytoplasmic volumes.

Representative question

Question 1

[Maximum number: 1]

Daughter cells usually receive equal amounts of cytoplasm as parent cells undergo cytokinesis. Which of the following is an exception?

A

Asexual reproduction by budding in yeast

B

Bacterial cell division

C

Cloning of lymphocytes during an immune response

D

Formation of a zygote during fertilization

Core Cell Division

  • Cell division produces daughter cells for growth, repair or reproduction; cytokinesis divides cytoplasm by a contractile ring in animals or a cell plate in plants.
  • DNA replication creates sister chromatids joined at centromeres before nuclear division.
  • Mitosis preserves chromosome number: chromosomes condense, align, sister chromatids separate and nuclei reform, producing genetically identical nuclei.
  • Meiosis follows one replication with two divisions: homologous chromosomes separate in meiosis I and sister chromatids in meiosis II, producing haploid cells.
  • Crossing over, independent orientation and random fertilization generate allele combinations.
  • Non-disjunction is failed chromosome separation and can produce aneuploid cells, including trisomy 21.
  • Identify stages in micrographs from chromosome condensation, equatorial alignment, separation and nuclear-envelope cues.

Concept essentials

  • Equal cytokinesis gives daughter cells similar cytoplasmic volumes.
  • Yeast budding is an example of unequal cytokinesis.
  • Oogenesis uses unequal cytokinesis to retain cytoplasm in the ovum.
  • Cytokinesis pattern affects daughter-cell size and resources.
ConceptIB Biology HL