Some stuff about cells

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The first cell was discovered by English scientist and microscopist Robert Hooke in 1665, who
observed cork cells underneath a microscope. He described their appearance as a honeycomb-like
network of cellulae. He used the term cell to describe the individual
units in plant tissue, as he only saw the cell walls because cork is
non-living and has no protoplasm. He drew these cells (Fig. 1) and
coined the word cell which comes from the Latin word cellula meaning
small compartment1.
The first living cells were observed by a Dutch scientist called Antony van Leeuwenhoek, who is
said to have made over 500 of his own `microscopes' but fewer than ten have survived until the
modern day. He seemed to have been inspired by Robert Hooke's book Micrographia about his own
discovery of the first cell. Leeuwenhoek discovered protozoa in 1674 and bacteria in 1683. It was
only after his discovery of bacteria that he wrote to the Royal Society about his observations. He
discovered the first living cell from his own plaque on his teeth, and repeated this on two females
and two old men who had never cleaned their teeth. He saw moving creatures in the plaque and
named them `animalcules' which means tiny creatures. In one of the samples from an old man he saw
so many of these `animalcules' that he said the water seemed to be alive3.
A timeline of the discovery of cells is shown in Fig. 2 below:
Fig. 2
Cell Theory
The cell theory states that all organisms are composed of similar units of organisation called cells.
This concept was articulated by Schleiden and Schwann in 1839. The suggestion was that the two
scientists were discussing their findings over a cup of coffee and Schwann was struck by how similar
his findings in animal cells were to Schleiden's findings in plant cells, and the two scientists then went
to Schwann's laboratory to look at his slides4.
Schwann published a book on Animal and Plant cells, fully acknowledging all other contributions and
had drawn the following conclusions about cells:

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The cell is the unit of structure, physiology and organization in living things.
The cell retains a dual existence as a distinct entity and a building block in the construction of
Cells form by free-cell formation, similar to the formation of crystals4.
Today we know that the first two tenets are correct but the third is wrong and was corrected to the
interpretation of cell formation by division. It was formally enunciated by Rudolph Virchow who said
`All cells only arise from pre-existing cells.…read more


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