Mitochondria are organelles that mediate the energy metabolism of the cells linked to the oxidation of biochemical compounds and generation of ATP that is used in various biochemical reactions as a source of energy. Larga number of mitochondria with many internal folds indicate that cell requires high amounts of energy and requires extensive production of ATP. As a result, it can be suggested that cell X requires lots of energy for certain mechanical, heat-related or conductive functions. As a result, cell X may represent muscle fibers, adipocytes of brown adipose tissue or neurons. In contrast, cell Y does not require much ATP as it is not involved in active energy metabolism and performs structural or storing function. Therefore, fat cells, bone cells or blood cells may be examples of cell Y.