The primary function of mitochondria is to produce ATP (adenosine triphosphate), which is the cell's primary energy source. This process is called cellular respiration.

Here's a breakdown:

1. Breakdown of glucose: Mitochondria break down glucose (sugar) through a series of chemical reactions called the Krebs cycle or citric acid cycle.

2. Electron transport chain: Electrons are passed along a chain of molecules, releasing energy. This energy is used to pump protons across the mitochondrial membrane, creating a concentration gradient.

3. ATP production: The flow of protons back across the membrane drives the production of ATP, using an enzyme called ATP synthase.

In addition to energy production, mitochondria also have other important functions, including:

* Apoptosis (programmed cell death): Mitochondria release signaling molecules that trigger apoptosis when a cell is damaged or no longer needed.

* Calcium signaling: They help regulate calcium levels within the cell, which is essential for various processes like muscle contraction and neurotransmission.

* Steroid synthesis: Some mitochondria are involved in the synthesis of certain steroid hormones.

Therefore, while ATP production is the primary function, mitochondria play a crucial role in various other cellular processes.