The protista kingdom is made up of members that have a single eukaryotic cell.
The kingdom protista is that formed by living organisms that have a single eukaryotic cell, which are classified as protists . Despite this definition provided by the dictionary of the Royal Spanish Academy ( RAE ), there are experts who also include multicellular organisms in the protist kingdom. In this sense, all the eukaryotic-type organisms that, due to their characteristics, are not part of the kingdoms of fungi, plants and animals, would make up the kingdom protista.
These differences in criteria mean that there is no single definition of the protist kingdom. Biologists do not fully agree on which organisms are protists and which should not be included in this classification .
There are those who divide the kingdom protista into three subkingdoms: archaezoa , euglenozoa and protozoa . The archaezoa subkingdom includes those protists that do not have mitochondria. In the subkingdom euglenozoa, also called chromista , protists appear that have mitochondria and that also carry out photosynthesis . Finally, in the protozoa (or rotozoan ) subkingdom, there are protists with mitochondria and no photosynthetic capacity.
Members of the protist kingdom
The difficulties in classification are due to the fact that protists sometimes resemble plants , while others resemble animals. However, the members of the kingdom protista are neither plants nor animals.
It can be said, in the broadest sense of the concept, that protists are unicellular or multicellular microorganisms that, for the most part, feed autotrophically , and that, on the other hand, cannot be included in the three remaining kingdoms of eukaryotes: that of plants ( Plantae ), that of animals ( Animalia ) and that of fungi ( Fungi ). It is important to note that there are no protists completely adapted to air, so even those that do not live in water depend on humidity to survive.
The protista kingdom is made up of microorganisms.
Its characteristics
Beings whose nutrition is considered autotrophic are those that can carry out the synthesis of the fundamental substances for their metabolism starting from inorganic substances, such that they do not need the presence of other organisms to nourish themselves. In other words, individuals of the protista kingdom produce their own food based on inorganic substances .
Furthermore, an autotrophic organism is capable of generating its organic matter and cell mass starting exclusively from carbon dioxide (an inorganic substance) to obtain carbon, and using light or certain chemical substances to obtain energy. Protists, for their part, can be both heterotrophic and photosynthetic autotrophs , although many of them combine both forms of nutrition.
In the first group, heterotrophs, we also include animals, since these are those individuals that must take advantage of third-party matter to manufacture complex organic molecules. To obtain energy, they break down the molecules of their prey.
Structure of the microorganisms that are part of the protista kingdom
Regarding their structure , protists do not have any type of tissue, although brown and red algae exhibit a degree of complexity that approaches tissue complexity, which includes the presence of plasmodesmata (the name given to the continuous units of cytoplasm that keep the cells of multicellular organisms connected to each other).
There are many multicellular individuals of the protista kingdom that have cell walls of various types of composition, while some unicellular individuals , such as diatoms, are usually covered with a theca (a resistant structure that can be compared to a shell, since it is found on the outside). of the cells of certain protists), or have reinforcements or scales.
The reproduction of protists can be sexual, with gametes , or asexual (in this case we speak of clonal reproduction ), although the most common thing is that both types of reproduction alternate. It should be noted that there is no embryo in either of them.