MITOCHONDRIA (Singular- MITOCHONDRION)
These are conspicuous, hollow sac liked cell organelles found in all eukaryotic cells except mature red blood corpuscles RBCs of mammals unlike most other organelles. The mitochondria are large enough to be resolved with light microscopes. That is why these were first observed and called sarcosomes as early as 1857 by Kolliker .Later these were renamed as bioblasts by altmann 1894 and as mitochondria by benda 1897.
Mitochondria widely very in their number shapes and sizes in different types of cells certain inicellular organisms contain a single large mitochondrion, but generally their number varies from 50 to several thousand depending upon the physiology or function of the concerned cells higher the rate of metabolism in a cell more is the number of mitochondria in it .The shape of mitochondria is variable but generally these are thread like ellipsoidal spherical or ovoid . These are approximately of the size of bacteria varying from 0.2 to 1.00 in girth and from 0.5 to 7.00 in length. These are however dynamic organelles in that these can change their shapes and size can passively move about with streaming of the cytosol and may multiply by division.
Structurally a mitochondrion consists of a fluid filled cavity surrounded. not by a single but by two rilaminar unit membrane an outer limiting membrane and somewhat thicker inner membrane .The outer membrane is smooth and straight. The inner membrane is infolded into the cavity, forming a number of simple or branched plate like sepa or tubular ridges , both called cristae . Being incomplete the cristae do not break the continuity of mitochondrial cavity. The part of the inner membrane covering the cristae bears numerous regularly spaced minute club shaped particles projecting into the mitochondrial cavity . These particles are called elementary or F0 F1 particles .Each particle has three distinct part a base piece embedded in the membrane , a projecting stalk or pedicel and a knob like head at the tip of the stalk .The two mitochondrial membrane are separated by a narrow fluid intermembrane or peri mitochondrial space which continues as a thin core into the cristae, The cristae. The fluid of mitochondrial cavity called mitochondrial matrix, is a dense and finely granular jelly like proteinaceous material.