Peroxisomes are specialized metabolic compartments bound by a single membrane. Inside the organelle there are enzymes that transfer hydrogen from various substrates to oxygen, creating hydrogen peroxide as a by-product. Some peroxisomes use oxygen to break down fatty acids into smaller molecules that will then be transported to mitochondria to be used as fuel for cellular respiration.

In the liver, peroxisomes detoxify alcohol and other poisons by transferring the hydrogen in them to oxygen. However, since hydrogen peroxide is also toxic, peroxisomes contain an enzyme to convert the substance to water.

Peroxisomes do not bud from the endomembrane system but grow by putting together proteins and lipids made in the cytosol. They multiply by splitting in two when they reach a certain size.