Classification of living beings in domains and kingdoms: characteristics and examples

Classification of living beings in domains and kingdoms: characteristics and examples
Posted on 23-02-2022

How are living things classified?

The current classification of living things includes three domains and seven kingdoms. Domains group living things by their cellular characteristics. The kingdoms group them by their evolutionary relationship. The classification system of living beings is structured as follows:

  1. Domain Eukarya, contains five kingdoms, which are:
  • animal kingdom
  • Kingdom Plantae
  • fungal kingdom
  • Kingdom Protozoa
  • Kingdom chromista or chromista
  1. Bacteria domain contains the bacteria kingdom.
  2. Archaea domain contains the archaea kingdom.


Living beings are all organisms with complex structures that are born, grow, reproduce and die. Given their variety and complexity, they are classified into various taxonomic categories for their study.

In many parts of the world, Robert Whittaker's classification system, which grouped living beings into five kingdoms (Monera, Fungi, Protista, Plantae, and Animalia), is still being misused. However, the correct (and current) model is that of the three domains, proposed by Carl R. Woese in 1977.

Eukarya Domain

The Eukarya domain is made up of all living things that have eukaryotic cells, which have a differentiated nucleus, protected by a membrane and with an organized cytoplasm. Some eukaryotes have mitochondria, organelles that generate energy.

The Eukarya domain is considered the most important, since the best-known kingdoms derive from it: AnimaliaPlantaeFungi, Chromista, and Protozoa.

animal kingdom

It is made up of all animals or multicellular organisms that develop from a zygote. They are classified into two large groups:

  • Vertebrates: have a bony structure (fish, amphibians, birds, reptiles, and mammals)
  • Invertebrates: they lack vertebrae (arthropods, molluscs, Porifera, cnidarians, echinoderms, flatworms, nematodes, and annelids).

Characteristics of the Animalia kingdom

  • Its reproduction can be sexual (like most of the organisms of this kingdom) or asexual, as is the case of Porifera (sea sponges) or other organisms.
  • Their nutrition is heterotrophic, that is, they depend on other organisms to live.
  • Their metabolism is aerobic, they require oxygen to live.
  • They are symmetrical: their structure starts from an axis and is divided into two equal parts.
  • They can move, either permanently (like humans) or temporarily, like corals, which stop moving when they reach adulthood.

Examples of the Animalia kingdom

  • The golden crucian fish ( Carassius auratus).
  • The Andean condor ( Vultur gryphus).
  • The squid ( Teuthida).
  • The tapeworm tapeworm ( Taenia solium.
  • The human being ( homo sapiens).

Kingdom Plantae

It is made up of all plants, which are multicellular eukaryotic organisms. In turn, the Plantae kingdom has two large groups:

  • Non-vascular plants: they lack a nutrient transport system. They have no roots, stems, or leaves.
  • Vascular plants: they have a differentiated vascular tissue, and have roots, stems, and leaves.

Characteristics of the kingdom Plantae

  • They are autotrophic organisms, that is, they generate their own food (through photosynthesis).
  • They cannot move.
  • Their metabolism is aerobic: they breathe in oxygen and expel carbon dioxide.
  • They may or may not have seeds.
  • They may or may not have flowers.

Examples of the kingdom Plantae

  • The ferns (filicópsidas).
  • Orchids ( Orchidaceae).
  • The orange tree or orange tree ( Citrus × Sinensis ).


fungal kingdom

All mushrooms, yeasts, and molds belong to the Fungi kingdom, which are multicellular organisms that generally develop in humid and aquatic environments. It is classified into three types:

  • Symbionts: are organisms that have a mutually beneficial relationship with other organisms.
  • Saprophytes or decomposers: they feed on the remains of other decomposing living beings.
  • Parasites: they feed on the organic matter generated by other living beings.

Characteristics of the Fungi kingdom

  • They reproduce asexually, by means of spores.
  • They feed by pinocytosis or phagocytosis, breaking down compounds into micromolecules.
  • Some organisms of the fungi kingdom are edible, such as certain types of mushrooms and mushrooms.

Examples of the kingdom Fungi

  • The yeast that is used in the bakery to create sourdoughs.
  • The Candidafungus , which causes skin and mucosal infections in humans.


Kingdom Protozoa (Protozoa)

The protozoa kingdom includes all eukaryotic organisms that cannot be considered animals, plants or fungi.

Characteristics of the Protozoa kingdom

  • They are unicellular eukaryotes.
  • Their nutrition can be heterotrophic, autotrophic or through photosynthesis.
  • They have the ability to move.
  • Its reproduction is asexual.
  • Their metabolic process is aerobic, they require oxygen to live.
  • They do not have a cell wall, so their shape is changeable.

Examples of the kingdom Protozoa

  • Amoeba or amoeba, parasite causing amebiasis or amebiasis.
  • Trypanosoma (Euglenozoa), an intracellular parasite.
  • Giardia (Metamonada), the parasite that causes the disease giardiasis.

Kingdom Chromista (chromists)

The chromista or chromista kingdom is made up of unicellular algae. This means that the living beings of the chromist kingdom cannot form tissues with each other, but they are capable of photosynthesis.

Characteristics of the Chromista realm :

  • Its organization is unicellular.
  • Its cells are eukaryotes.
  • They can reproduce sexually or asexually.
  • Their diet can be of different types.
  • Their mobility is varied.

Examples of the Chromista realm

  • Brown algae, which usually live on rocky shores.
  • Diatom algae, which are found anywhere there is water (seas, rivers, lakes, and humid forests).


Bacteria domain or superkingdom

The Bacteria domain is made up of prokaryotic organisms, that is, organisms whose cells lack a differentiated nucleus. For now, all beings in this domain belong to the bacteria kingdom.

Kingdom Bacteria

The beings of the bacterial kingdom do not have a nucleus or organelles inside the cell.

Characteristics of the Bacteria kingdom

  • Its DNA is called a nucleoid, and it is found in the cytoplasm of its single cell.
  • They lack locomotion, some have organelles to move and others remain immobile.
  • Their reproduction is asexual and they require the duplication of their genetic material to perpetuate themselves.
  • Bacteria are pleomorphic organisms, that is, the same species can take several forms.

Examples of the kingdom Bacteria

  • Escherichia coli, found in the human digestive tract.
  • The Idonella sakaiensis, a bacterium that has the property of degrading plastic.

Archaea domain or superkingdom

It encompasses unicellular prokaryotic organisms without a differentiated nucleus, like bacteria. However, they are living beings with genetic and metabolic characteristics closer to eukaryotic organisms, although their evolutionary path is completely different. They can be present in the water of the oceans, in different types of soil, and even in the human digestive tract. The domain or superkingdom Archaea contains the kingdom Archaea.

kingdom archaea

The microorganisms of the Archaea kingdom have unique characteristics that place them somewhere between the Eukarya and Bacteria domains.

Characteristics of the Archaea kingdom

  • They have a very wide nutritional variety: they feed on hydrogen, sugars, or ammonia.
  • They can use carbon or sunlight for energy.
  • They reproduce asexually, after duplicating their DNA.
  • Pathogenic archaea are not known: their form of biological interaction is not harmful to other organisms.

Examples of the kingdom Archaea

  • Mhetanosarcina is a type of archaea that produces methane.
  • Ignicoccus, an archaea that lives in marine hydrothermal vents.


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