Domains and Kingdoms
The Archaea singular archaeon) constitute a domain or kingdom of single celled organism. These microbes are prokaryotes, meaning that have no cell or any other membrane-bound organelles in their cells.
- Domain Bacteria is composed of organisms that are much more common than Archaea and live almost anywhere. There are morebacteria in a person's mouth than there are people in the world. Many are decomposers, some are photosynthesizers, and a few cause disease.
The Domain Eukarya arose from the first prokaryotic organisms more than 1.7 billion years ago. It includes all of the organisms with eukaryotic cells--that is, those with membranous organelles (including mitochondria and chloroplasts). The organisms in this domain will be the focus of our classifications; indeed, they represent the vast majority of organisms we see each day. In terms of our classification questions, members of the domain have the following characteristics.
The Domain Archaea wasn't recognized as a major domain of life until quite recently. Until the 20th century, most biologists considered all living things to be classified as either a plant or an animal.
Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals.
- mostly unicellular, some are multicellular (algae)
The Kingdom Fungi includes some of the most important organisms, both in terms of their ecological and economic roles.
Plants, also called green plants, are multicellular eukaryotes of the kingdom Plantae.
Animals are multicellular, eukaryotic organisms of the kingdom Animalia.