Mitochondra (IMAGE) Arizona State University Caption Mitochondria are the energy powerhouses in eukaryotic cells. One popular hypothesis claims these organelles were a pre-requisite to the transition from simpler prokaryotes like bacteria and archaea to larger, more complex eukaryotic organisms. The new study challenges this assumption. Credit Graphic by Jason Drees Usage Restrictions None License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.