Briefly describe Mitochondria.

Mitochondria is a Greek word. Mitos - thread and chondroitin - granule. (Singular: mitochondrion).
Kolliker first observed mitochondria. Later Altmann named them as Bioplasts. Finally, Benda called them Mitochondria.
Shape:
They are typically sausage-shaped. They can be cylindrical, rod, spherical, granular, filamentous or thread like also.
 
Size:
0.2 micron meters to 2-micron meters.

Location:
They are distributed in cytoplasm bounded by a double membrane envelope. Two membranes are separated by peri-mitochondrial space.

Membrane shape:
1) Outer membrane: smooth
2) Inner membrane: fingers like structure called cristae, which possess a small rounded body called F1 particles or Oxysomes. They help in electron transport.
The interior cavity is filled with a proteinaceous matrix containing lipids, proteins, circular DNA and RNA.

Note:
Mitochondria are absent in bacteria and the red blood cells of mammals. It is the powerhouse of the cell. It stores energy in the form of ATP.

Mitochondria is also known as power house of the cell. Now why this is power house?
We all know that electricity is energy and this energy comes from power house, similarly in biology enery is ATP i.e adenosine triphosphate which forms in mitochondriya and this is why it is called power house.

Structure:
it is double membrane bound organelle.
There are five distinct parts to a mitochondrion. They are:

Outer mitochondrial membrane
Intermembrane space
the inner mitochondrial membrane
the cristae space and
the matrix
*Important thing about mitochondria is it has their own genome.