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.
"Mitochondria" is a plural term; which is appropriate
because it is not usual to find a single "mitochondrion" (which
may also be referred to as a "chondriosome"). Mitochrondria are structures
within cells whose purpose is energy production. Mitochondria
contain adenosine triphosphate (ATP) together with enzymes that are involved
in the metabolic activities of the cell. Mitochondria are bounded by
double membranes, the inner of which is folded inwards, forming projections
- hence the representation of mitochondria in diagrams.
The quantity of mitochondria
within cells varies with the type
See the Revision page about Cell
Structure for further information including a diagram of the
structure of a basic cell including mitochondria and
all the other organelles.