It’s an interesting story. Mitochondria are a part of the cells of all living things except bacteria. Cells have what we call “organelles.” These are parts of the cell that do specific jobs. Ribosomes are parts of the cell that help make proteins. Even bacteria have them. Non-bacterial cells have a bunch of other organelles. The nucleus (NEW-klee-us) holds the DNA. It contains all of the recipes to make an entire individual, whether that individual is a mushroom, an amoeba, or a person.

Cells that aren’t bacteria have mitochondria. The mitochondria are organelles that help turn the energy in food into energy in another molecule called ATP. About all you need to know about ATP is that it is a quick energy source the cell uses to do work. I like to explain biology by telling little stories, so stay with me for a moment.

The power that comes into your home could come from burning coal, from water flowing through a dam, a nuclear power plant, or a solar farm. But the electricity is all the same. You don’t have to shovel coal into your lamp to give it power. In the same way, you may eat pizza, tofu, or tacos, but the energy in that food is used to make one energy source, ATP. Mitochondria are often compared to power plants for that reason. They transform energy from one source to another. They don’t make energy. No living thing does.

Here's the really amazing thing: mitochondria have their own DNA. That’s just weird. Scientists think that a long time back, say over 2 billion years ago, a bacterial cell ended up in a non-bacterial cell. Maybe it was a parasite. Maybe it was eaten. But the big cell turned out to be a pretty great place for the bacteria to live. The bacteria divided, and when the big cell divided, each half took some bacteria with it. Over a long period of time, the descendants of bacteria and the big cells started to depend on each other. Now they can’t live apart. The descendants of the free-living bacteria are now mitochondria. This site has some good pictures of mitochondria: Mitochondria.

All of our mitochondria came from our mother, so mitochondrial DNA is useful in figuring out family trees.

When individuals of one species live inside individuals of another species, it’s called endosymbiosis (EN-doh-SIM-by-oh-sis). Can you think of other examples of species that live inside each other?

Mitochondria are organelles (think organs, but for cells) that take sugar and combine it with oxygen to make energy. This is how we use oxygen to keep ourselves alive.

Mitochondria are present in all animal cells (including humans), all plants, all fungi, all algae, and almost all protozoa. They contain their own DNA and are descended from free-living bacteria, billions of years ago.

You may hear that "the mitochondrion is the powerhouse of the cell" to describe its function. In animal cells, this is true, but not in plant cells. This is because plants contain another organelle, the chloroplast, which is even more powerful.

The word mitochondrion comes from Greek, meaning a grain-like body with threads. The plural of mitochondrion is mitochondria.

Mitochondria play a role in the conversion of chemical energy. The cell cannot use glucose directly. Instead the cell uses adenosine triphosphate (ATP) as the energy source for most of its functions. The cell must break down glucose in cellular respiration.

Cellular respiration can be anaerobic or aerobic. Anaerobic respiration does not require oxygen but only produce 2 ATP per glucose molecule. Aerobic respiration is more efficient and produces 30 to 32 ATP per glucose. Aerobic respiration takes place inside mitochondria.

All lives on Earth can be classified into two groups, prokaryotes and eukaryotes. Prokaryotes do not have a nucleus inside their cell and include all bacteria. Eukaryotes have a nucleus and include plants, yeasts, mushrooms, and animals. Almost all eukaryotes have mitochondria. There are handful unicellular eukaryotes that either significantly reduce or lose their mitochondria.

As of the time of writing, all multicellular organisms except *Henneguya zschokkei*, a parasite infecting salmon, have mitochondria. However, all mature red blood cells in mammals, including human, have lost their mitochondria and the nucleus.

The mitochondria, you might hear for many years to come, is the powerhouse of the cell. It is a membrane-bound organelle (like a little organ for the cell that has a protective layer that controls what chemicals go in and out of it) and is required for most cells to make energy efficiently.

Most human cells have mitochondria, and cells that require a lot of energy (think of muscle cells that need a lot of energy when you exercise) have a lot of mitochondria. Some cells don't have any mitochondria, like red blood cells. Red blood cells get rid of mitochondria when they're mature enough so that they have space to do other things (carry oxygen!). Red blood cells still can make energy but are much less efficient because they don't have mitochondria.

Hi Carolina! Mitochondria are the powerhouses of the cell! [this is a pretty famous phrase by the way :) ]. They take in nutrients, break them down, and create energy-rich molecules (called ATP) for the cell to function. As a result, mitochondria keep the cell full of energy, thus known as the powerhouses of the cell. This process of breaking down nutrients to create energy in mitochondria is called "oxidative phosphorylation" and requires oxygen. That is also part of the reasons why we humans need oxygen to live.

The number of mitochondria per cell varies quite widely. In humans, the red blood cells do not contain any mitochondria (a notable exception), while the liver cells and muscle cells have a lot of mitochondria, as those cells require a lot of energy to function effectively. As a bonus, red blood cells get energy from the process called "glycolysis" which does not require oxygen, while other cells with mitochondria can perform both glycolysis and oxidation phosphorylation.

All human cells have mitochondria except our red blood cells. The mitochondria produces lots of energy in our cells. Outside the mitochondria, our cells can produce a little energy from food. Inside our mitochondria, oxygen is used to produce lots more energy from the food.