Why protists is not a kingdom

In fact, the protists can be sorted into between three and ten proposed kingdoms, depending on which researchers are doing the sorting.

Scientists are trying to create these groups based on evolutionary relationships. The goal in forming kingdoms is to group all the descendants from a common ancestor into one group.

Treating the protists as a single group can work in certain areas of biology. For example, it might not matter in medicine which specific protist kingdom is causing an infection in a patient if the treatment for all protist infections is the same. The only real constant rule is that all protists are eukaryotes, meaning that they are organisms with more complex cells than bacteria.

Most protists have a single independent cell, though some seaweeds break this rule. Most protists have a single defined nucleus holding the bulk of their DNA, though some ciliates have multiple nuclei and flagellates do not have a defined nucleus. As a group, it is difficult to find a definition that describes all protists perfectly.

What Are the Five Subdivisions of Kingdoms? What Are the Two Prokaryotic Kingdoms? Crabs That Are Related to Spiders. General Characteristics of Protista. According to Simpson, nowadays "protozoa" is a term of convenience used in reference to a subset of protists, and is not a taxonomic group. The term protista, meaning "the first of all or primordial" was introduced in by German scientist Ernst Haeckel. He suggested Protista as a third taxonomic kingdom, in addition to Plantae and Animalia, consisting of all "primitive forms" of organisms, including bacteria International Microbiology, Since then, the kingdom Protista has been refined and redefined many times.

Different organisms moved in and out notably, bacteria moved into a taxonomic kingdom of their own. American scientist John Corliss proposed one of the modern iterations of Protista in the s. His version included the multicellular red and brown algae, which are considered to be protists even today. Scientists, often concurrently, have debated kingdom names and which organisms were eligible for example, versions of yet another kingdom, Protoctista had been proposed over the years.

However, it is important to note the lack of correlation between taxonomy and evolutionary relationships in these groupings. According to Simpson, these groupings were not monophyletic, meaning that they did not represent a single, whole branch of the tree of life; that is, an ancestor and all of its descendants. Today's classification has shifted away from a system built on morphology to one based on genetic similarities and differences.

The result is a family tree of sorts, mapping out evolutionary relationships between various organisms. In this system there are three main branches or "domains" of life: Bacteria, Archaea both prokaryotic and Eukarya the eukaryotes. Within the eukaryotic domain, the protists are no longer a single group.

They have been redistributed amongst different branches of the family tree. According to Simpson, we now know most of the evolutionary relationships amongst protists, and these are often counterintuitive. He cited the example of dinoflagellate algae, which are more closely related to the malaria parasite than they are to diatoms another group of algae or even to land plants. Still, there are pressing questions that remain.

This point is called the "root" of the eukaryotic tree of life. Pinpointing the root will cement the understanding of eukaryotic origins and their subsequent evolution. As author Tom Williams said in a article published in the journal Current Biology, "For the eukaryotic tree, the root position is critical for identifying the genes and traits that may have been present in the ancestral eukaryote, for tracing the evolution of these traits throughout the eukaryotic radiation, and for establishing the deep relationships among the major eukaryotic groups.

Protists are responsible for a variety of human diseases including malaria, sleeping sickness , amoebic dysentery and trichomoniasis. Malaria in humans is a devastating disease. It is caused by five species of the parasite Plasmodium , which are transmitted to humans by female Anopheles mosquitoes, according to the Centers for Disease Control and Prevention CDC.

The species Plasmodium falciparum infects red blood cells, multiplies rapidly and destroys them. Infection can also cause red blood cells to stick to the walls of small blood vessels. This creates a potentially fatal complication called cerebral malaria according to the CDC.

Freeman, , struggled heroically to justify the Protista they preferred the term Protoctista kingdom. All human cells are fathered ultimately by sperm, which bear undulipodia, but no one has suggested that humans are therefore protists. Genomics has made it clear that far from being a single kingdom, the protists are a phylogenetically diverse group.

But the alternative to grouping them together is to separate them into tiny fiefdoms, each of which is equivalent on the tree of Eukaryota to what appear from our perspective to be the more significant kingdoms. Carl Woese's ribosomal RNA-based phylogenetic tree has branches for slime molds, Entamoeba amoeba , ciliates protozoa , flagellates e.

In , the International Society of Protistologists divided Eukaryota into six different "supergroups" but controversy immediately erupted as to whether the categories reflected phylogenetic reality. The fracturing of kingdom Protista into a plethora of principalities is a pedagogical nightmare and a headache for zoology students everywhere.

The effort to understand the incredible diversity of life remains one of the most difficult tasks that humans have undertaken.