Mitochondria

Minute, rod-shaped or granular bodies, about 1/4 to 3¬µm in length or diameter that occur in the cytoplasm of most cells responsible for aerobic respiration that breaks down food in the presence of oxygen and carbon dioxide, leading to the generation of energy.  Thus, they are the ‘powerhouses’ of a cell.  They contain many of the enzymes of the cell, particularly those required for the citric acid or Krebs cycle.  They are not only the site for the Krebs cycle, but also the electron transport chain and thus for the cell’s energy production.  Consequently, they are most numerous in cells with a high level of metabolic activity. 

See Acrosome, Cell, Cytoplasm, Cytoskeleton, Electron transport chain (or respiratory chain), Energy, Enzyme, Eukaryote cell (or organism), Krebs cycle (or tr-carbooxylic, Nucleoid, TCA, cycle), Maximal aerobic power, Metabolism, Oocytes, Organelles