Cells are of two types: eukaryotic, which contain a nucleus, and prokaryotic cells, which do not have a nucleus, but a nucleoid region is still present. Prokaryotes are single-celled organisms, while eukaryotes can be

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All cells, whether prokaryotic or eukaryotic, have a membranethat envelops the cell, regulates what moves in and out (selectively permeable),

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Many cells also have structures which exist wholly or partially outside the cell membrane. These structures are notable because they are not protected from the external environment by th

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Cell specialization/differentiation
Multicellular organisms are organisms that consist of more than one cell, in contrast to single-celled organisms.
In complex multicellular organisms, cells specialize into different cell typesthat are adapted to particular

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The origin of cells has to do with the origin of life, which began the history of life on Earth.
Origin of the first cell
There are several theories about the origin of small molecules that led to life on the early Earth.

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• 1632–1723: Antonie van Leeuwenhoek taught himself to make lenses, constructed basic optical microscopes and drew protozoa, such as Vorticella from rain water, and

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Replication
Cell division involves a single cell (called a mother cell) dividing into two daughter cells. This leads to growth in multicellular organisms (the growth of tissue) and to procreation (vegetative reproduction) in unicellular organisms

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