Prokaryotes have adapted structures that allow them to thrive in many habitats, including fimbriae, capsules, flagella, and cell walls. They reproduce quickly through binary fission and genetic recombination, allowing populations to evolve rapidly in response to environmental changes. Prokaryotes use different methods of nutrition, including photoheterotrophy, chemoautotrophy, and chemoheterotrophy. They also show metabolic adaptations for oxygen levels and nitrogen fixation. Molecular systematics is leading to a phylogenetic classification of prokaryotes, with Archaea and bacteria in their own domains based on adaptations to extreme environments.