(BIOLOGY) The fundamental unit
of terrestrial life. Cells are self-replicating and may exist on their
own as independent organisms, as in the case of bacteria, archaea, and
protista, or may form colonies or tissues, as in higher life-forms.
The two main types of cells are prokaryotic
cells and eukaryotic cells.
Each cell consists of protein-rich material that is differentiated into
cytoplasm and a nucleus.
Forming a boundary around the cytoplasm is a cell
membrane, which in plants and some microorganisms is, in turn, surrounded
by a cell wall.
Cells were discovered in 1665 by the English scientist Robert Hooke
who first observed them through a primitive microscope. Hooke coined
the term "cell," in a biological context, when he described the microscopic
structure of cork as being like a tiny,
bare room or monk's cell.
- (MATHEMATICS) (i) A three-dimensional
object that is part of a higher-dimensional object, such as a polychoron.
A cell is related to higher-dimensional objects in the way that a face,
or (two-dimensional) polygon, is related
to higher-dimensional objects. For example, a cell is to a 4-dimensional
polytope, or polychoron, what a face
is to a 3-dimensional polytope, or polyhedron.
Often polytopes are classified simply by how many cells they have. For
example, the tesseract has eight cells,
each one of which is a cube. (ii) The fundamental spatial unit operated
on by the rules of a cellular automaton
during one generation.