Mitochondria diagram (labeled structure)

A mitochondria diagram shows a mitochondrion cut lengthways: a smooth outer membrane, a narrow intermembrane space, and an inner membrane folded into cristae that surround the fluid matrix. ATP synthase particles stud the cristae, and the matrix holds the mitochondrion’s own circular DNA and ribosomes. Mitochondria make most of a eukaryotic cell’s ATP by cellular respiration, which is why they are often called the powerhouse of the cell.

Last updated 26 October 2026

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Labeled diagram of a mitochondrion in longitudinal section. Labels: outer membrane, intermembrane space, inner membrane, cristae, ATP synthase, matrix, mitochondrial DNA and ribosomes. — Mitochondria diagram by LabCanvas (labcanvas.com), CC BY 4.0

Mitochondria diagram without labels — Mitochondria diagram by LabCanvas (labcanvas.com), CC BY 4.0

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Parts of the mitochondria and what they do

Mitochondria: labelled parts
#	Part	What it is or does
1	Outer membrane	Smooth phospholipid bilayer that surrounds the whole mitochondrion and separates it from the cytoplasm.
2	Intermembrane space	The narrow space between the two membranes, where protons (H+) build up during the electron transport chain.
3	Inner membrane	Second phospholipid bilayer; holds the electron transport chain and ATP synthase and controls what enters the matrix.
4	Cristae	Folds of the inner membrane that greatly increase its surface area for the electron transport chain and ATP synthase.
5	ATP synthase	Enzyme complex in the inner membrane that uses the flow of protons back into the matrix to make ATP (chemiosmosis).
6	Matrix	The fluid inside the inner membrane, where pyruvate is oxidised and the citric acid cycle takes place.
7	Mitochondrial DNA	The mitochondrion’s own small, circular DNA, which carries genes for some of its own proteins.
8	Ribosomes	Mitochondrial ribosomes in the matrix that make some of the mitochondrion’s proteins.

How to label a mitochondria diagram

Draw the outer membraneDraw a large rounded oval, longer than it is tall. Go over it with a second line just inside to show the membrane as a band.
Draw the inner membraneDraw a second oval a little inside the first, leaving a narrow gap between them: this gap is the intermembrane space.
Fold the inner membrane into cristaeInstead of a smooth line, push the inner membrane inward as finger-like folds from the top and bottom edges. Each fold is two lines joined by a rounded tip, and the inside of each fold opens into the intermembrane space.
Add ATP synthaseDraw small lollipop shapes (a short stalk and a round head) along the cristae, with the heads pointing into the matrix.
Fill the matrixAdd two or three small closed loops for mitochondrial DNA and small dots for ribosomes in the open space between the cristae.
Label with leader linesPut the labels around the outside and draw straight lines to each part, with no lines crossing. Make sure the inner membrane label points to the membrane itself, not the space beside it.

Mitochondrion vs chloroplast

Feature	Mitochondrion	Chloroplast
Found in	Almost all eukaryotic cells, including plant and animal cells	Plant cells and algae
Main process	Cellular respiration: releases energy from food to make ATP	Photosynthesis: captures light energy to make sugars
Membranes	Outer and inner membrane	Outer and inner membrane, plus a separate system of thylakoids
Inner folds or sacs	Cristae (folds of the inner membrane)	Thylakoids, stacked into grana
Fluid inside	Matrix	Stroma
Own DNA and ribosomes	Yes	Yes
Makes ATP with ATP synthase	Yes, using energy from food molecules	Yes, using light energy

Stages of cellular respiration and where they happen

Glycolysis happens in the cytoplasm, outside the mitochondrion. It splits one glucose into two pyruvate molecules and gives a small net gain of ATP and NADH.

Pyruvate oxidation and the citric acid cycle happen in the matrix. Pyruvate is carried into the mitochondrion and converted to acetyl CoA, releasing carbon dioxide; the citric acid cycle then releases more carbon dioxide and loads electrons onto NADH and FADH₂.

Oxidative phosphorylation happens on the inner membrane and cristae. The electron transport chain passes electrons from NADH and FADH₂ to oxygen, the final electron acceptor, which forms water. The energy released pumps protons from the matrix into the intermembrane space. Protons then flow back into the matrix through ATP synthase, which uses that flow to make most of the cell’s ATP. This use of a proton gradient is called chemiosmosis.

Why the inner membrane is folded

The electron transport chain and ATP synthase are built into the inner membrane, so the more inner membrane a mitochondrion has, the more ATP it can make. Folding the membrane into cristae packs a large surface area into a small organelle. Cells that use a lot of energy, such as muscle cells, have many mitochondria.

Why mitochondria have their own DNA

Mitochondria contain their own DNA and ribosomes and divide on their own inside the cell. These features support the endosymbiotic theory: mitochondria are thought to descend from bacteria that were taken up by an ancestral eukaryotic cell and lived inside it. Most mitochondrial proteins are now encoded by genes in the nucleus, but the mitochondrial DNA still carries a small set of its own genes.

Quick quiz

1. What are the folds of the inner mitochondrial membrane called?

Thylakoids
Cristae
Grana
Villi

Answer: b) Cristae. Cristae are folds of the inner membrane; thylakoids and grana belong to chloroplasts.

2. Where does the citric acid cycle take place?

In the cytoplasm
In the intermembrane space
In the matrix
In the outer membrane

Answer: c) In the matrix. Pyruvate oxidation and the citric acid cycle happen in the mitochondrial matrix.

3. Where do protons build up during the electron transport chain?

In the matrix
In the intermembrane space
In the nucleus
Outside the cell

Answer: b) In the intermembrane space. The electron transport chain pumps protons from the matrix into the intermembrane space.

4. What does ATP synthase use to make ATP?

Light energy directly
The flow of protons back into the matrix
Glucose inside the outer membrane
Ribosomes

Answer: b) The flow of protons back into the matrix. Protons flowing down their gradient through ATP synthase drive ATP production (chemiosmosis).

5. Which feature supports the idea that mitochondria came from bacteria?

They have cristae
They have their own DNA and ribosomes
They are oval
They are found in muscle cells

Answer: b) They have their own DNA and ribosomes. Their own DNA and ribosomes are key evidence for the endosymbiotic theory.

Frequently asked questions

What does a mitochondria diagram show?

A labelled mitochondria diagram shows the outer membrane, the intermembrane space, the inner membrane folded into cristae, the matrix, ATP synthase particles on the cristae, and the mitochondrial DNA and ribosomes in the matrix.

How do you draw a mitochondrion?

Draw an oval for the outer membrane, a second oval just inside it for the inner membrane, then turn the inner line into finger-like folds (cristae) that reach into the middle. Add small lollipop shapes for ATP synthase, loops for DNA and dots for ribosomes in the matrix, then label each part.

What are the parts of the mitochondria?

Outer membrane, intermembrane space, inner membrane, cristae, matrix, ATP synthase, mitochondrial DNA and ribosomes.

What are cristae and why are they important?

Cristae are the folds of the inner mitochondrial membrane. They increase the surface area available for the electron transport chain and ATP synthase, so the mitochondrion can make more ATP.

What happens in the mitochondrial matrix?

Pyruvate oxidation and the citric acid cycle (Krebs cycle) take place in the matrix. The matrix also contains the mitochondrion’s DNA and ribosomes.

Why are mitochondria called the powerhouse of the cell?

Because they make most of the ATP a eukaryotic cell uses, by breaking down food molecules in cellular respiration. ATP is the energy currency that powers most cell work.

Do plant cells have mitochondria?

Yes. Plant cells have both chloroplasts, for photosynthesis, and mitochondria, for cellular respiration. Almost all eukaryotic cells have mitochondria.

Sources

Facts on this page follow these introductory textbooks (OpenStax, CC BY 4.0). The diagram is a simplified illustration; organelles are not drawn to scale.