Mitochondria are brownish red. If humans didn’t have melanin in their skin, they would be the color of mitochondria, the only colored part of a cell.
Often called the “powerhouses” of the cell, mitochondria are essential to life because they use oxygen to produce energy. Mitochondria take in nutrients and break them down to create molecules rich in energy for the cell. The name of this process, which happens completely in mitochondria, is cellular respiration.
Depending on the amount of energy needed, some cells have thousands of mitochondria, and some have none. For example, cells in muscles need a lot of energy, so they have a lot of free-floating mitochondria. If a cell needs more energy for survival, it can produce more mitochondria.