Syllabus Edition

First teaching 2023

First exams 2025

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Mitosis: Skills (SL IB Biology)

Revision Note

Marlene

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Marlene

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Identifying Phases of Mitosis

  • Cells undergoing different stages of the cell cycle can be identified using photomicrographs taken from microscope slides
  • Cells undergoing certain stages of the cell cycle have distinctive appearances

Interphase

  • As cells spend the majority of the cell cycle in this stage then most cells will be in this stage
  • The chromatin is visible (however chromosomes are not) so the nuclei have a dark appearance

Prophase

  • Chromosomes are visible
  • The nuclear envelope is breaking down

Metaphase

  • Chromosomes are lined up along the middle of the cell

Anaphase

  • Chromosomes are moving away from the middle of the cell, towards opposite poles
  • As they are pulled from the centromere through the cytoplasm, the chromosomes tend to have a characteristic 'V' shape

Telophase

  • Chromosomes have arrived at opposite poles of the cell
  • Chromosomes begin to uncoil (are no longer condensed)
  • The nuclear envelope is reforming

Cytokinesis

  • Animal cells: a cleavage furrow forms and separates the daughter cells
  • Plant cells: a cell plate forms at the site of the metaphase plate and expands towards the cell wall of the parent cell, separating the daughter cells

Identification of phases

Micrograph showing a cell undergoing prophase (P)

Micrograph showing cells undergoing metaphase (M) and anaphase (A) (1), downloadable AS & A Level Biology revision notes

Micrograph showing cells undergoing metaphase (M) and anaphase (A)

Micrograph showing cells undergoing metaphase (M) and anaphase (A), downloadable AS & A Level Biology revision notes

Micrograph showing cells undergoing metaphase (M) and anaphase (A)

Micrograph showing a cell undergoing anaphase (A), downloadable AS & A Level Biology revision notes

Micrograph showing a cell undergoing anaphase (A)

Examiner Tip

It is important to be able to recognise each mitotic stage from electron micrographs and to be able to explain why that cell is in the stage you have selected. It can be difficult to tell prophase and telophase apart in some photomicrographs. In prophase, there is only one group of chromosomes in the cell while in telophase there are two groups, one at each pole.

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Marlene

Author: Marlene

Expertise: Biology

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.