Which cell organelle is known as the 'powerhouse of the cell'?

Mitochondria (singular: mitochondrion) are rod-shaped or oval organelles found in the cytoplasm of almost all eukaryotic cells, both plant and animal. They were first seen in the 19th century; the name "mitochondrion" was given by Carl Benda in 1898.

Mitochondria are called the "powerhouses of the cell" because they produce most of the cell's energy. They carry out aerobic respiration, in which glucose and other food molecules are broken down in the presence of oxygen to release energy. This energy is stored in molecules of ATP (adenosine triphosphate), which is called the "energy currency" of the cell. The Krebs cycle (citric acid cycle) takes place in the matrix of the mitochondria, and the electron transport chain works on the inner membrane.

Structure: each mitochondrion has two membranes. The outer membrane is smooth. The inner membrane is folded into finger-like projections called cristae, which increase the surface area for respiration. The fluid inside is called the matrix.

Mitochondria are semi-autonomous organelles. They have their own circular DNA and their own ribosomes (70S type, like bacteria), so they can make some of their own proteins and divide on their own. This supports the endosymbiotic theory, which says that mitochondria were once free-living bacteria that came to live inside larger cells. Mitochondrial DNA is inherited almost entirely from the mother.

Cells that need a lot of energy, such as muscle cells, heart cells and liver cells, have large numbers of mitochondria. Red blood cells of mammals have none.

Why not the other options?

• ✗Chloroplasts are found in plant cells and carry out photosynthesis; they are the "kitchens" of the cell.
• ✗The nucleus is the "control centre" of the cell.
• ✗The endoplasmic reticulum transports materials within the cell.