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6.1. Cell concept

Cell concept

cell is the morphological and functional unit of every living being. In fact, the cell is the smallest element that can be considered alive, since it fulfills the functions of nutrition, relationship and reproduction. Thus, living organisms can be classified according to the number of cells they have: if they only have one, they are called unicellular (such as protozoa or bacteria, microscopic organisms); if they have more, they are called multicellular. In the latter, the number of cells is variable: from a few hundred, as in some nematodes, to hundreds of billions (1014), as in the case of humans.