Substrates that are broken down in the cytoplasm are brought to the mitochondria to be transformed into a chemical known as adenosine triphosphate (ATP) which is used later. Mitochondria have two membranes. Their internal fluid called matrix is ​​used to produce energy for the creation of ATP by using ribosomes and enzymes to break down carbohydrate products. The second (inner) membrane of mitochondria invaginates to develop cristae. Cristae gives up much more surface area to house the products needed to create ATP. Mitochondria also contribute to cell differentiation and cell death (Mader, Windelspecht