Edexcel International A Level Biology

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3.1 Cell Theory

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The Cell as a Unit of Life

  • Until microscopes became powerful enough to view individual cells, no-one knew for certain what living organisms were made from
  • A scientist called Robert Hooke is thought to be the first person to view cells, using the term 'cell' to describe these newly discovered structures
  • Matthias Schleiden and Theodor Schwann were two other scientists who studied animal and plant cells
    • In 1837 they came up with the idea that all living organisms are made of cells
    • This idea is known as ‘cell theory’
    • The cell theory is a unifying concept in biology, meaning that it is universally accepted
  • Cell theory includes three main ideas
    • All living organisms are made up of one or more cells
    • Cells are the basic functional unit in living organisms
    • New cells are produced from pre-existing cells
  • The cells of all living organisms share some common features
    • Cell surface membrane
    • Cytoplasm
    • DNA
    • Ribosomes
  • Beyond these common features different cell types contain different structural elements and combinations of organelles, e.g.
    • Prokaryotic cells have no internal membranes and smaller ribosomes
    • Eukaryotic cells have several internal membrane-bound organelles and larger ribosomes
  • When examined under a microscope it is possible to see the ultrastructure of different cell types
    • Cell ultrastructure refers to the internal structures of the cell

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Author: Alistair

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.