The current classification of living things includes three domains and seven kingdoms. Domains group living beings by their cellular characteristics. The kingdoms are grouped by their evolutionary relationship. The classification system of living beings is structured as follows:
1. Domain Eukarya , contains five kingdoms, which are:
- Animalia Kingdom
- Kingdom Plantae
- fungi kingdom
- Kingdom Protozoa
- Chromista or chromista kingdom
2. Domain Bacteria , contains the bacteria kingdom.
3. Domain Archaea , contains the kingdom archaea.
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 study.
In many parts of the world, Robert Whittaker’s classification system, which grouped living beings into five kingdoms (Monera, Fungi, Protista, Plantae and Animalae), continues to be used incorrectly. However, the correct (and current) model is the three domains model, proposed by Carl R. Woese in 1977.
The Eukarya domain is made up of all living beings that have eukaryotic cells, which have a differentiated nucleus, protected with a membrane and 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: Animalia , Plantae , Fungi, Chromista and Protozoa .
It is made up of all multicellular animals or organisms that develop from a zygote. They are classified into two large groups:
- Vertebrates: have a bone structure (fish, amphibians, birds, reptiles and mammals)
- Invertebrates: they lack vertebrae (arthropods, mollusks, poriferans, cnidarians, echinoderms, flatworms, nematodes and annelids).
Characteristics of the Animalia kingdom
- Its reproduction can be sexual (like most organisms in 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 from the kingdom Animalia
- The golden crucian carp ( Carassius auratus ).
- The Andean condor ( Vultur gryphus ).
- The squid ( Teuthida ).
- The tapeworm ( Taenia solium.
- The human being ( homo sapiens ).
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 oxygen and expel carbon dioxide.
- They can have seeds or lack them.
- They can have flowers or lack them.
Examples from the kingdom Plantae
- Ferns (filicopsidae).
- Orchids ( Orchidaceae ).
- The orange tree or orange tree ( Citrus × sinensis ).
The Fungi kingdom includes all mushrooms, yeasts and molds, 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 organic matter generated by other living beings.
Characteristics of the Fungi kingdom
- They reproduce asexually, using spores.
- They feed by pinocytosis or phagocytosis, breaking down compounds into micromolecules.
- Some organisms in the fungi kingdom are edible, such as certain types of mushrooms and mushrooms.
Examples from the kingdom Fungi
- The yeast used in baking to create sourdoughs.
- The Candida fungus , which causes infections in the skin and mucosa of humans.
Kingdom Protozoa (protozoans)
The kingdom protozoa includes all eukaryotic organisms that cannot be considered animals, plants or fungi.
Characteristics of the protozoa kingdom
- They are unicellular eukaryotic beings.
- Its 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 that causes amoebiasis or amoebiasis.
- Trypanosoma (Euglenozoa), an intracellular parasite.
- Giardia (Metamonada), the parasite that causes the disease giardiasis.
Chromista Kingdom (chromists)
The chromista or chromista kingdom is made up of unicellular algae. This means that living beings in the chromatic kingdom cannot form tissues among themselves, but they are capable of photosynthesis.
Characteristics of the Chromista kingdom :
- Its organization is unicellular.
- Its cells are eukaryotic.
- They can reproduce sexually or asexually.
- Their diet can be of different types.
- Their mobility is varied.
Examples from the Chromista kingdom
- Brown algae, which usually live on rocky coasts.
- Diatom algae, which are found anywhere where water exists (seas, rivers, lakes and humid forests).
It may interest you; Eukaryotic cell
Domain or superkingdom Bacteria
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.
Beings from the bacteria 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 only 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, meaning that the same species can take on several forms.
Examples from the kingdom Bacteria
- Escherichia coli , found in the human digestive tract.
- Idonella sakaiensis, a bacteria that has the property of degrading plastic.
Domain or superkingdom Archaea
It includes unicellular prokaryotic organisms without a differentiated nucleus, like bacteria. However, these are living beings with genetic and metabolic characteristics closer to eukaryotic organisms, although their evolutionary route is completely different. They can be present in ocean water, in different types of soil and even in the human digestive tract. The domain or superkingdom Archaea contains the kingdom Arquaea.
Microorganisms of the kingdom Archaea have unique characteristics that place them somewhere between the Eukarya and Bacteria domains .
Characteristics of the kingdom Archaea
- They have a very wide nutritional variety: they nourish themselves with hydrogen, sugars or ammonia.
- They can use carbon or sunlight for energy.
- They reproduce asexually, after duplicating their DNA.
- There are no known pathogenic archaea: their form of biological interaction is not harmful to other organisms.
Examples from the kingdom Archaea
- Mhetanosarcina , a type of archaea that produces methane .
- Ignicoccus , an archaea that lives in marine hydrothermal vents.
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