Mitochondrion (plural, mitochondria) is found abundantly in eukaryotic cells. It is about 1 to 10μm long. Eukaryotic cells have one or more mitochondria. The number of mitochondria is directly proportionally to the metabolic activity. Active cells have more mitochondria compared less active cells. Example: sperm cells contain more mitochondria.
Mitochondrion has double membrane system which make up by phospholipid bilayer embedded by proteins. It consists of outermost membrane facing cytoplasm and inner membrane. Outer membrane is smooth and permeable to small molecules. Inner membrane is less permeable and folded repeatedly inside to form cristae. The folded cristaes provide larger surface area, thus enhancing the cellular respiration. It is studded with tiny speheres, about 9nm diameter enzyme ATP synthase. Inner membrane divides mitochondrion into intermembrance space and mitochondrial matrix. Electron chain transport occur at inner membrane. Intermembrane space normally has lower pH than matrix as hydrogen ions are released into it by the activity of electron transport and generate ATP in chemiosmosis.
Different enzymes as well as the mitochondrial DNA and ribosomes are found inside the matrix. Matrix is the place where link reaction and Krebs cycle occur. Organic compounds are broken down to carbon dioxide and water to form ATP in mitochondrion.