Cell Theory (Edexcel IAL Biology)

The Cell as a Unit of Life

Spec point — 3.1

• 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