The fluid that fills the mitochondria is called the matrix. The matrix is a gel-like substance that contains enzymes, DNA, ribosomes, and other components essential for the mitochondria’s function. It plays a crucial role in the production of energy through the process of cellular respiration.
Within the matrix, the citric acid cycle (also known as the Krebs cycle) takes place, which is a key part of generating ATP, the energy currency of the cell. The matrix also helps in the regulation of metabolic processes and the synthesis of important molecules.