KEY CONCEPT The current tree of life has three domains.

Classification is always a work in progress. The tree of life shows our most current understanding. New discoveries can lead to changes in classification. Until 1866: only two kingdoms, Animalia and Plantae Animalia Plantae

Classification is always a work in progress. The tree of life shows our most current understanding. New discoveries can lead to changes in classification. Until 1866: only two kingdoms, Animalia and Plantae Plantae Animalia 1866: all single-celled organisms moved to kingdom Protista Protista

Classification is always a work in progress. The tree of life shows our most current understanding. New discoveries can lead to changes in classification. Until 1866: only two kingdoms, Animalia and Plantae Animalia Protista Plantae 1866: all single-celled organisms moved to kingdom Protista 1938: prokaryotes moved to kingdom Monera Monera

Classification is always a work in progress. The tree of life shows our most current understanding. New discoveries can lead to changes in classification. Until 1866: only two kingdoms, Animalia and Plantae Protista Plantae Animalia 1866: all single-celled organisms moved to kingdom Protista 1938: prokaryotes moved to kingdom Monera Fungi 1959: fungi moved to own kingdom Monera

Classification is always a work in progress. The tree of life shows our most current understanding. New discoveries can lead to changes in classification. Until 1866: only two kingdoms, Animalia and Plantae Animalia Protista Fungi Plantae 1866: all single-celled organisms moved to kingdom Protista 1938: prokaryotes moved to kingdom Monera Archea Bacteria 1959: fungi moved to own kingdom 1977: kingdom Monera split into kingdoms Bacteria and Archaea

The three domains in the tree of life are Bacteria, Archaea, and Eukarya. Domains are above the kingdom level. proposed by Carl Woese based on rRNA studies of prokaryotes domain model more clearly shows prokaryotic diversity Analyze: Why did Woese propose classifying bacteria and archaea into separate domains, rather than just separate kingdoms? Analyze: Why are protists, plants, fungi and animals classified into the same domain but into different kingdoms? The Tree of Life The most recent classification system divides life into three domains, which include six kingdoms. The distances between branches are proportional to the number of differences in rRNA sequences among these species.

Domain Bacteria includes prokaryotes in the kingdom Bacteria. one of largest groups on Earth classified by shape, need for oxygen, and diseases caused Figure: The most common shapes of bacteria are rods, spirals and spheres. Many bacteria are named after their shape like this one shown at the right. Spirochaeta: spiral. (colored SEM; magnification 5000 X)

Domain Archaea includes prokaryotes in the kingdom Archaea. cell walls chemically different from bacteria differences discovered by studying RNA known for living in extreme environments Figure:Pyrococcus furiosus, can be found in undersea hot vents and in the sand surrounding sulfurous volcanoes. These organisms live without oxygen and can grow in temperatures higher than the boiling point of water. (colored SEM; magnification 6500 X)

Domain Eukarya includes all eukaryotes. kingdom Protista Figure: Zooflagellates have flagella that help them move through water. (colored SEM; magnification unknown)

Domain Eukarya includes all eukaryotes. kingdom Protista kingdom Plantae Figure: The titan arum plant produces a flower that smells like carrion, or rotting meat. Beetles that eat carrion are attracted by this odor and often wind up pollinating the flower. This ecological relationship is an example of commensalism.

Domain Eukarya includes all eukaryotes. kingdom Protista kingdom Plantae kingdom Fungi Figure: Many sac fungi are sac- or cup-shaped or have cupshaped indentations. Sac fungi include moss cup fungi, also known as scarlet elf cups.

Domain Eukarya includes all eukaryotes. kingdom Protista kingdom Plantae kingdom Fungi kingdom Animalia Figure: Sea cucumbers are fleshy animals that live on the ocean floor.

Bacteria and archaea can be difficult to classify. transfer genes among themselves outside of reproduction blurs the line between “species” more research needed to understand prokaryotes bridge to transfer DNA Figure: In conjugation, genetic material transfers between prokaryotes, producing genetic variation. A conjugation bridge forms from the donor cell to a recipient cell. (TEM; magnification 6000 X)