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
