Explore the structure and function of our intracellular energy factories


A transmission electron micrograph of a mitochondrion in a chick embryo cell.


Prof. R Bellairs/Wellcome Images

Mitochondria are very important organelles in our cells – they provide them with chemical energy through aerobic respiration.

A single mitochondrion (as shown in the image to the right) has a very simple structure, adapted to its function as a factory for energy. It has two membranes, with the inner membrane folded into inward projections, known as cristae. You can see these extending across the mitochondrion pictured. 

It is here that the final stage of aerobic respiration takes place, with an electron transport chain generating energy in the form of adenosine triphosphate (ATP). (Check out our article on aerobic respiration for more detail, or have a look at our poster to see the different stages of the process.)

The more cristae present in a mitochondrion, the larger the surface area of its inner membrane – which increases its capacity for aerobic respiration (and so energy production). Typically, the more metabolically active a cell, the more mitochondria it will have, and with more cristae per mitochondrion. 

Inside the organelle, the fluid around the cristae is known as the mitochondrial matrix. This hosts the earlier link reaction and Krebs cycle stages of aerobic respiration.

The darker spots in the image are ribosomes occupying the mitochondrial matrix. These are involved in protein synthesis, which you can read more about in our article ‘Working together’.


About this resource

This resource was first published in ‘Exercise, Energy and Movement’ in August 2016.

Cell biology
Exercise, Energy and Movement
Education levels:
16–19, Continuing professional development