A cell is the basic unit of living organisms (both plants and animals)
that is capable of reproducing itself exactly. That is, there are
components within cells (organelles), but they do not reproduce themselves
independently of the cell(s) of which they are a part.
The cell membrane keeps the cell together by containing the organelles
Cell membranes consist of lipids and protein and are selectively-permeable
to allow materials to move both into and outside of the cell. Animal
cells have cell membranes - as opposed to the cell walls of plant
See the Revision page about Cell
Structure for further information including a diagram of the structure
of cell membranes.