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7.3. Kingdoms of living beings

The five kingdoms

Although since Aristotle (4th century BC) classified organisms into two kingdoms, animal and plant, there have been many more attempts at classification. The best known, the one proposed by Whittaker (1969), which grouped living beings into five great kingdoms according to the type of cell, number of cells and type of nutrition . Later, Woese (1990) proposed a classification in which living beings were grouped into three domains: archaea and bacteria (prokaryotes) and eukarya (eukaryotes).

Haeckel (1866)
Three Kingdoms
Two Groups
Four Kingdoms
Five Kingdoms
Three Domains
Animal Eukaryota Animal Animal Eukarya
Plant Plant Plant
Protoctist Fungi
Protist Protist
Prokaryota Monera Monera Archaea

Tomado de

Kingdom moneras

All living things that belong to this kingdom are unicellular, made up of a single prokaryotic cell, although they can sometimes form colonies. They can live in different media (watersoilair, inside other living beings,...). Two large groups of microscopic organisms are included:

  • Archaebacteria: bacteria that live in environments with extreme characteristics.
  • Eubacteria: the typical bacteria and the cyanobacteria.

Protoctists kingdom

They are unicellular and multicellular organisms made up of eukaryotic cells. It groups living beings that cannot be classified in the other kingdoms, since they are not animalsplants, or fungi. Their size is small and they do not have the capacity to form tissues.
It includes two very different groups:

  • The Protozoa, unicellular organisms, such as amoebas and paramecia.

  • Algae, which can be unicellular or multicellular, are unicellular photosynthetic organisms or with very simple organization such as diatom algae and green algae.

Kingdom fungi (fungi)

Formed by unicellular and multicellular eukaryotic beings, they reproduce by means of spores. This kingdom includes mushroomsyeasts, and molds. Although they have common characteristics with plants and animals, they are so peculiar that they cannot be included in another kingdom.

Fungi (like plants) have a cell wall, although plants are made of cellulose and fungi are made of chitin.

Although they may look like plants because they live fixed in one place, they do not photosynthesize. They are heterotrophic organisms (like animals), and they have to feed on substances created by other living beings. They can get their food in three ways:

  • Saprophytes: feed on decaying organic debris.
  • Parasites: They feed on the organism in which they live.
  • Symbionts: They feed through their association with a plant.

Kingdom metazoa (animals)

They are all eukaryotic and multicellular beings. They are heterotrophs, they do not carry out photosynthesis, and they feed on substances produced by other living beings. Its cells do not have a cell wall and are specialized to form tissuesorgans, apparatus and systems. They have a nervous system, which gives them sensitivity and response to different stimuli and they have the ability to move. For example, this kingdom includes insectsmammalsjellyfishfish, ...

Metaphyta kingdom (vegetables)

Formed by eukaryotic cells, they are multicellular beings , which can form tissues and organs such as rootsstems and leavesThey are autotrophic beings, with the ability to carry out photosynthesis and make their food from simple inorganic substances (watermineral salts and CO2). Their cells have a cell wall made of cellulose. They cannot be moved. Some metaphytes are trees, ferns, etc.


Although living things can be very different, they all come from the same common ancestor. From the first cell that originated, and over millions of years and successive generations, different living beings emerged.

Biodiversity (or biological diversity) is the variety of species that live on Earth or in a given ecosystem.

Living beings do not live in isolation, but are related to individuals of their own species and to others belonging to other species, so when an alteration occurs in one species of the ecosystem, many others can be affected. That is why we must always bear in mind the importance of biodiversity.