Protist kingdom

ביולוג

2022

We explain what the protista kingdom is, its characteristics and how it is classified. Also, how is their nutrition, reproduction and examples.

The protista kingdom groups a group of generally unicellular organisms.

What is the kingdom protista?

The kingdom protista, also called protoctista, is one of the groups in which the biology classify living things eukaryotes that cannot be classified as animals, floors neither mushrooms.

The Protist kingdom is a paraphyletic group (it does not contain all the descendants of a common ancestor) and includes a very diverse set of organisms usually unicellular either multicellular simple that do not form tissues, both autotrophs What heterotrophs. Their enormous variety makes it difficult to characterize them, except in the common features of all eukaryotic beings, that is, possessors of cells with a cell nucleus definite.

The existence of a protist kingdom was proposed in 1969 in the theory of the five kingdoms of life, but it is currently considered a term in disuse and its members tend to be classified within the other branches of eukaryotic life.

The word protista comes from the Greek and means "primordial" or "first of the first". Protoctista, similarly, translates as "first creatures."

Characteristics of protists

There is not much in common between the various forms of protists.

The kingdom Protista is not a monophyletic group, that is, all the organisms included in it did not evolve from a common ancestor.In the biological classification that gives them the status of a kingdom (that of Robert Whittaker in 1969), the characteristics that group protists are those of being simple unicellular or multicellular eukaryotic organisms that do not form any type of tissue.

Except for their relative evolutionary simplicity, there is not much in common between the different protists, which present different models of nutrition, reproduction, locomotion and cellular structures.

Classification of protists

The kingdom of the protists is traditionally divided into very different supergroups:

  • Archeplastids. They have plastids surrounded by an outer and an inner membrane. This group includes the most primitive green and red algae, precursors of plant life, especially terrestrial life.
  • Chromeveolated. They are a very diverse group that could have originated as a result of secondary endosymbiosis, in which an ancestral cell engulfed a red algae (secondary endosymbiosis is the process that occurs when a eukaryotic cell surrounds and absorbs another eukaryotic cell). This group includes the alveolates, which have cortical alveoli, that is, flattened vesicles that form a flexible film that supports the plasma membrane. Within the alveolates dinoflagellates, apicomplexans and ciliates are grouped; and the stramenopiles, which have motile cells with two flagella, one of which has small hair-like projections extending from the axis. In this group are the oomycetes, diatoms, golden algae and brown algae.
  • Rizarios. They are diverse organisms of the amoeboid or flagellate type that, frequently, have testas (shells). They include the foraminifera, which have hard shells through which cytoplasmic projections (pseudopods) extend; and actinopods, which have endoskeletons (internal shells) through which axopods (filamentous pseudopods) extend.
  • Excavated.They are characterized by having mitochondria atypical, greatly modified. They are organisms formerly classified as flagellates, which have a central groove of feeding (they are heterotrophs), although many may have chlorophyll as a result of endosymbiosis with green algae. They include diplomonads, parabasalids, euglenoids, and trypanosomes.
  • Unicons. They have cells that have a single flagellum or are amoebas no flagella. Within this group are the amoebozoans, characterized by forming pseudopods ("fingers") with extensions of their cytoplasms; and the opisthochondria, which are devoid of flagella or have a single posterior flagellum in motile cells. It is believed that this group would have given rise to the animalia and fungi kingdoms.

Protist nutrition

Some protists lead a parasitic life.

Protists can have metabolisms autotrophs or heterotrophs, depending on whether they have chloroplasts (chlorophyll) to carry out the photosynthesis or if, instead, they lack them and must feed on the organic material surrounding (by osmosis or ingestion or phagocytosis).

Many of them have both nutritional mechanisms simultaneously, and some lead a parasitic existence: they enter multicellular organisms and feed on them, causing diseases.

However, protists are originally aerobic (they use oxygen for their metabolic processes), with the exception of those that evolved to live in environments where oxygen is scarce.

reproduction of protists

The reproduction of protists can be both sexual What asexual, and sometimes the same species can alternate between one model and another, according to the conditions of the environment. environment.

Sexual reproduction occurs through the generation of gametes and cell fusion, while asexual reproduction occurs by cell fission Y mitosis.

Importance of protists

Protists gave rise to the rest of the kingdoms of eukaryotic organisms.

Protists are a diverse and difficult group to classify, but fundamental to the emergence of life as we know it. They were the first eukaryotic organisms to arise in the primitive seas of the Land and from them the life it took various evolutionary paths, and gave rise to the rest of the eukaryotic kingdoms: plants, animals, and fungi.

Protists constitute a previous and relatively common step to all these forms of eukaryotic life, including humans, and their study is also the study of eukaryogenesis, that is, of the appearance of the cell nucleus in the evolutionary history of primitive prokaryotes.

examples of protists

Plasmodia are transmitted through the bite of an infected mosquito.

Some known protists are the following:

  • Paramecia. They are free-living, ciliated unicellular organisms, abundant in the waters stagnant and puddles.
  • amoebas. Called amoebas or amoebas, they are unicellular protists that move and feed by generating pseudopodia or "fingers" with their cytoplasm, which gives them a changing and dispersed shape. They can be free-living or parasitic.
  • Plasmodium. They are a genus of parasitic protists of which up to 175 species are known, which are transmitted to hosts. vertebrates through the bite of an infected mosquito. They are the cause of the disease known as malaria or malaria.
  • Glaucophyta. They are unicellular freshwater algae, of which about 13 are known. species, and which are sometimes included among the plants. They are generally made up of individual cells, but they can also share the cell wall of their parent, since their reproduction is always asexual.
  • Choanozoa.It is a group linked to animals and fungi, and which constitutes a kind of intermediate step between these two groups of eukaryotes. can be divided into holomycota (similar to fungi) and holozoa (similar to animals).
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