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First teaching 2023

First exams 2025

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Cell Differentiation (HL) (HL IB Biology)

Revision Note

Cara Head

Author

Cara Head

Last updated

Cell Differentiation

  • One important process that occurred in the development of the cell was cell compartmentalisation 
  • This enabled unicellular organisms to develop specialised functions through specific areas of their cell
    • One example is the nucleus region which contains DNA molecules
    • Another example is the compartmentalisation of energy producing areas formed by the endosymbiosis of mitochondria
  • However, even with specialised compartments unicellular organisms have their limitations, and so multicellular organisms evolved 
  • In complex multicellular organisms eukaryotic cells become specialised for specific functions
  • Specialisation enables the cells in a tissue to function more efficiently as they develop specific adaptations for that role. The development of these distinct specialised cells occurs by differentiation
  • These specialised eukaryotic cells have specific adaptations to help them carry out their functions
  • For example, the structure of a cell is adapted to help it carry out its function (this is why specialised eukaryotic cells can look very different from each other)
  • Structural adaptations include:
    • The shape of the cell
    • The organelles the cell contains (or doesn’t contain)
  • For example:
    • Cells that make large amounts of proteins will be adapted for this function by containing many ribosomes (the organelle responsible for protein production)

Example of a specialised cell, a red blood cell

red-blood-cell-diagram

The biconcave shape of red blood cells (erythrocytes) increases the surface area available for oxygen absorption

Gene expression

  • Every nucleus within the cells of a multicellular organism contains the same genes, that is, all cells of an organism have an identical genome
  • Despite cells having the same genome, they have a diverse range of functions because during differentiation certain genes are expressed ('switched' on)
  • Whether a gene is expressed or not is triggered by changes in the environment
  • Controlling gene expression is the key to development as the cells differentiate due to the different genes being expressed
  • Once certain genes are expressed the specialisation of the cell is usually fixed so the cell cannot adapt to a new function

expression-of-genes-diagram-part-1expression-of-genes-diagram-part-2expression-of-genes-diagram-part-3Expression of genes resulting in cell differentiation

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Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding