domain

Domain is the highest classification rank of living organisms. In Domain there are three categories: eukaryotes, bacteria, and archaea.

• eukaryotes: any organism whose cells contain a nucleus and other structures (organelles) enclosed within membranes.
• bacteria: cell membrane contains ester bonds; cell wall made of peptidoglycan; have only one RNA polymerase; react to antibiotics in a different way than archea do.
• archaea: cell membrane contains ether linkages; cell wall lacks peptidoglycan; genes and enzymes behave more like Eukaryotes; have three RNA polymerases like eukaryotes; and extremophiles

(Many bacteria and archaea are prokaryotic. Prokaryotes are single-celled organisms that lack a membrane-bound nucleus (karyon), mitochondria, or any other membrane-bound organelles.)

kingdom

Kingdom is the second highest taxonomic rank. Kingdoms are divided into smaller groups called phyla. The United States uses a system of six kingdoms: animalia, plantae, fungi, protista, archaea, and bacteria.

• animalia: animals are complex multicellular, heterotrophic organisms. they generally feed on plants and other animals. animal cells are enclosed by a plasma membrane.
• plantae: plants are multicellular, autotrophic organisms. they make their own food through the process of photosynthesis, which uses light, oxygen and water. plants are made up of eukaryotic cells, which are different from other organismic cells in that they contain chloroplasts and a rigid cell wall.
• fungi: fungi are multicellular, eukaryotic organisms that feed by breaking down dead organic matter. fungi are unable to move and have no sensory abilities, which make them dissimilar to plants and animals. however, fungi are unable to perform photosynthesis and their cells are more similar to those found in the animal kingdom.
• protista: protists are organisms that do not fit clearly into any other kingdom. most protists are unicellular, which prevents them from being classified as a plant, animal or fungus. however, they typically have complex cells that are quite different from eubacteria and archaebacteria. examples of protists include algae and protozoans.
• archaea: archaebacteria are single-celled organisms that live in extreme environments. they have been found in underground thermal vents and hot springs with boiling temperatures, limited oxygen and high acidity. Most archaebacteria are chemotrophic, relying on the chemicals around them to produce their own food.
• bacteria: eubacteria are single-celled, eukaryotic organisms that live in diverse environments. eubacteria can be photoautotrophs, saprophytes or symbionts. Although eubacteria are usually the cause of the most common illnesses, the majority of eubacteria are harmless in the natural world. eubacteria cells are covered by a capsule and DNA information contained in special structures called ribosomes.

phylum