Eubacteria are commonly known as 'true bacteria' to distinguish them from the Archaea. They are prokaryotic organisms found in nearly every habitat on Earth. They possess peptidoglycan in their cell walls, a feature that is absent in both Archaea and Eukarya, making them a distinct and fundamental domain of life.

Bacteria are prokaryotic, unicellular organisms that lack a membrane-bound nucleus and other organelles. In the classic five-kingdom system proposed by Robert Whittaker, all prokaryotic organisms were grouped into the Kingdom Monera. While modern molecular phylogenetics often uses a three-domain system, the term Monera remains a standard reference in historical botanical and biological classification contexts.

Members of the Kingdom Plantae are defined as eukaryotes because their cells contain membrane-bound organelles, including a distinct nucleus that houses their genetic material. Prokaryotes, such as bacteria, lack these complex internal structures. Viruses are not classified as eukaryotes or prokaryotes because they are not considered living cells, and fungi belong to their own separate kingdom.

Archaea are well-known for their ability to thrive in extreme environments, including those that are strictly anaerobic (lacking oxygen). Many methanogenic archaea, for example, live in oxygen-free habitats like deep-sea hydrothermal vents, hot springs, and the digestive tracts of animals. While some bacteria are also anaerobic, the domain Archaea is particularly noted for its prevalence in these harsh, oxygen-depleted conditions.

Autotrophic organisms are defined by their ability to produce complex organic compounds from simple inorganic substances present in their environment. This process usually involves capturing energy from sunlight (photoautotrophs) or through chemical reactions (chemoautotrophs) to fuel their metabolic needs.

Organisms in the kingdom Animalia are heterotrophic, meaning they cannot synthesize their own food and must ingest or absorb organic material from other organisms. This nutritional strategy requires animals to consume plants, other animals, or organic debris to obtain energy and essential nutrients.

Archaea are well-known for their ability to thrive in extreme environments, such as high-temperature hydrothermal vents, highly acidic pools, or extremely salty conditions. These organisms, often called extremophiles, possess unique biochemical adaptations in their cell membranes and enzymes that allow them to survive where most other life forms cannot.

Biological diversity, or biodiversity, encompasses the variety of all living organisms, including plants, animals, and microorganisms. When referring to the variety of plants specifically, it is called plant diversity. The question asks for the term describing the variety of organisms in different taxa, and while 'Plants diversity' is a specific subset, the context of biological classification often encompasses the broader spectrum of life forms found in nature.

A taxon (plural: taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. These units are placed at various levels in the taxonomic hierarchy, such as species, genus, family, order, class, phylum, or kingdom. The use of the term 'taxon' allows scientists to refer to a group at any level of classification without specifying the exact rank, facilitating clear communication in systematic studies.

Systematics is the scientific study of the diversification of living forms, both past and present, and the relationships among living things through time. It involves taxonomy, which is the naming and classification of organisms, and phylogenetics, which studies the evolutionary history and relationships between different groups of organisms.