Definition · Plain-language
Mitochondria
Mitochondria are the organelles where most of a cell’s energy is released, through aerobic respiration — often called the powerhouse of the cell.
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The powerhouse of the cell
Mitochondria (singular: mitochondrion) are the organelles where aerobic respiration releases energy from food. They take in glucose and oxygen and transfer the energy stored in glucose into a usable chemical form, the molecule ATP, which the rest of the cell can spend on its activities. This is why they are nicknamed the "powerhouse of the cell". They do not create energy from nothing — energy cannot be created — but transfer it from one store to another, releasing it in small, controlled amounts the cell can use safely.
Structure: a double membrane
A mitochondrion is enclosed by two membranes. The smooth outer membrane forms the boundary, while the inner membrane is highly folded into ridges called cristae. These folds greatly increase the surface area available for the reactions of respiration, so a small organelle can do a lot of energy work. Inside is a jelly-like matrix where many of those reactions take place. Mitochondria also carry a small amount of their own DNA, separate from the DNA in the nucleus — a clue to their ancient evolutionary origin.
More mitochondria where more energy is needed
The number of mitochondria in a cell reflects how much energy that cell uses. Muscle cells, which contract repeatedly, and nerve cells, which constantly send signals, are packed with mitochondria. Cells with gentler energy demands have fewer. This link makes mitochondria a good example of how structure matches function in biology: where a job needs more energy, the cell builds more of the organelle that supplies it. Both plant and animal cells contain mitochondria.
Key facts
At a glance
- Definition: the organelle where most aerobic respiration releases energy
- Nickname: the powerhouse of the cell
- Main job: transfers energy from glucose into a usable form (ATP)
- Structure: enclosed by a double membrane; inner one folded into cristae
- Found in: both plant and animal cells
- More where: cells with high energy demand, e.g. muscle and nerve cells
Common misconceptions
What people often get wrong
Often heard: Mitochondria create or make energy for the cell.
Actually: Energy cannot be created. Mitochondria transfer energy already stored in glucose into a usable chemical form (ATP), releasing it in controlled amounts. They convert one energy store into another rather than producing energy from nothing.
Often heard: Only animal cells have mitochondria.
Actually: Both plant and animal cells contain mitochondria, because both respire to release energy. Plant cells also have chloroplasts for photosynthesis, but they still need mitochondria for respiration just as animal cells do.
Often heard: Every cell has the same number of mitochondria.
Actually: The number varies with energy demand. High-energy cells such as muscle and nerve cells contain many mitochondria, while less active cells have far fewer. The count reflects how much energy a particular cell needs.
Going deeper
