MITOCHONDRIA (Singular-  MITOCHONDRION)

These are conspicuous, hollow  sac liked  cell organelles found in all eukaryotic  cells except  mature  red  blood  corpuscles RBC_s 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.