Mitochondria are the powerhouses of cells, generating the energy cells need to perform their tasks and stay alive. Researchers have been studying mitochondria for some time because when these cell organelles don't function as well as they should, several diseases develop. In this photograph of cow cells taken under a microscope, the mitochondria have been stained bright yellow to visualize them in the cell. The large blue dots are the cell nuclei and the gray web is the cell cytoskeleton.