Both animal (A) and plant (B) cells have a cell membrane (1), nucleus (2), and cytoplasm (3). But in plants the cell wall is covered with a rigid coating of cellulose (4).
Typical animal cell.
The cell in biology
In biology, the cell is 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.
The cell in mathematics
In mathematics, a cell may refer to either of the following. (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 four-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.