Like bacteria, archaeans have no internal membranes and their DNA exists as a single loop called a plasmid. However, their tRNAs have a number of features that differ from all other living things.

Only archaea are known to produce methane. Methane-producing archaea are called methanogens. Halophilic archaea prefer a concentration of salt close to saturation and perform photosynthesis using bacteriorhodopsin. Some archaea, based on fossil evidence, are among the oldest organisms on earth.

Archaea: cells do not contain a nucleus; they have a different cell wall from bacteria. Eukarya: cells do contain a nucleus.

There are four different types of archaean cell walls. One type is composed of pseudopeptidoglycan, which is similar to peptidoglycan in morphology but contains different sugars in the polysaccharide chain. The other three types of cell walls are composed of polysaccharides, glycoproteins, or pure protein.

As the evolutionary story is usually told, first came the prokaryotes: the archaea and bacteria, which are often envisioned as simple bags of enzymes without an intricate structure.

A possible answer is: Bacteria contain peptidoglycan in the cell wall; archaea do not. The cell membrane in bacteria is a lipid bilayer; in archaea, it can be a lipid bilayer or a monolayer. Bacteria contain fatty acids on the cell membrane, whereas archaea contain phytanyl.

Members of the archaea include: Pyrolobus fumarii, which holds the upper temperature limit for life at 113 °C (235 °F) and was found living in hydrothermal vents; species of Picrophilus, which were isolated from acidic soils in Japan and are the most acid-tolerant organisms known—capable of growth at around pH 0; and …

These names have stuck, though a battle continues over whether another word — prokaryotes, meaning Bacteria plus Archaea together — has any legitimate use. And it is no longer believed that Archaea are any older than Bacteria, as their name and the New York Times headline might imply.

No definitive virulence genes or factors have been described in archaea to date. Nevertheless, archaea may have the means, and they certainly have the opportunity, to cause disease. Archaea share some characteristics with known pathogens that may reflect the potential to cause disease.

“The detected archaea are probably involved in nitrogen turnover on skin, and are capable of lowering the skin pH, supporting the suppression of pathogens,” said Moissl-Eichinger. “Bacteria with the same capacities are already used as skin probiotics, potentially improving skin moisture and reducing body odors.

The main archaea detected in humans and animals belong to the phylum Euryarchaeota, which includes the five known orders of methanogens (Halobacteriales, Methanobacteriales, Methanosarcinales, Methanomicrobiales, and Methanococcales) [21]; a sixth order has also been proposed [22].

Recent data suggest that the Archaea provide the major routes for ammonia oxidation in the environment. Archaea also have huge economic potential that to date has only been fully realized in the production of thermostable polymerases.

Their role in biogeochemical cycles is essential and they contribute to important ecosystem processes including creation, maintenance and functioning of soil. Bacteria and archaea are the only organisms that can gain energy from redox reactions that do not involve carbon compounds.

Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. Archaea are a major part of Earth’s life. They are part of the microbiota of all organisms. In the human microbiome, they are important in the gut, mouth, and on the skin.

This phylogeny overturned the eukaryote-prokaryote dichotomy by showing that the 16S rRNA tree neatly divided into three major branches, which became known as the three domains of (cellular) life: Bacteria, Archaea and Eukarya (Woese et al. 1990).

Plants, Animals, Protists, Fungi, Archaebacteria, Eubacteria. How are organism placed into their kingdoms?

The most influential system, the ‘Whittaker’ five kingdom structure, recognises Monera (prokaryotes) and four eukaryotic kingdoms: Animalia (Metazoa), Plantae, Fungi and Protista.

Living things are divided into five kingdoms: animal, plant, fungi, protist and monera. Living things are divided into five kingdoms: animal, plant, fungi, protist and monera.

Until recently the system devised by Robert Whittaker in 1968 was widely adopted. Whittaker’s classification scheme recognizes five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia.

Animalia

Whittaker

Carl Woese et

Five Kingdom Classification System

• Monera (includes Eubacteria and Archeobacteria) Individuals are single-celled, may or may not move, have a cell wall, have no chloroplasts or other organelles, and have no nucleus.
• Protista.
• Fungi.
• Plantae.
• Animalia.
• A “mini-key” to the five kingdoms.

Herbert F. Copeland

Woese

All viruses that have an RNA genome, and that encode an RNA-dependent RNA polymerase (RdRp), are members of the kingdom Orthornavirae, within the realm Riboviria.

All living organisms can be broadly divided into two groups — prokaryotes and eukaryotes — which are distinguished by the relative complexity of their cells. Bacteria and archaea are prokaryotes, while all other living organisms — protists, plants, animals and fungi — are eukaryotes.

Some severe diseases of humans are caused by protists, primarily blood parasites. Malaria, trypanosomiasis (e.g., African sleeping sickness), leishmaniasis, toxoplasmosis, and amoebic dysentery are debilitating or fatal afflictions.

Algae, singular alga, members of a group of predominantly aquatic photosynthetic organisms of the kingdom Protista. Algae have many types of life cycles, and they range in size from microscopic Micromonas species to giant kelps that reach 60 metres (200 feet) in length.

Lesson Summary

• Animal-like protists are called protozoa. Most consist of a single cell.
• Plant-like protists are called algae. They include single-celled diatoms and multicellular seaweed.
• Fungus-like protists are molds. They are absorptive feeders, found on decaying organic matter.