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6.3. Size, shape and quantity

Cell size, shape and number

The cell shape is very variable, depending on the cell type, age, and its function. It also depends on whether it is free or is part of a tissue. The cell has the shape that allows it to perform its function with the lowest possible energy expenditure.

Free-living cells are usually spherical due to surface tension. Those that are part of tissues have a polyhedral shape. Others, like neurons, are star shaped. Or fibrillar, like muscular, or flat, like epithelial.

The cell size is also very variable, ranging from 0.001 mm of bacteria (1 micron) to the yolk of an ostrich egg (almost 9 cm), although its size is usually between 0.01 and 0.2 mm.

There is no relationship between the size of the cells and that of the multicellular individual. That is, the cells of a very tall person are no larger than those of a small child.

Escalas comparadas

By Guillaume Paumier, Philip Ronan, NIH, Artur Jan Fijałkowski, Jerome Walker, Michael David Jones, Tyler Heal, Mariana Ruiz, Science Primer (National Center for Biotechnology Information), Liquid_2003, Arne Nordmann & The Tango! Desktop Project [CC BY-SA 2.5], via Wikimedia Commons

The number of cells that a multicellular being has is also variable. Although there are exceptions, such as the Caenorhabditis elegans worm that always have 959 cells. In the rest of the species there is a relationship between the size of the individual and the number of cells.