What is the difference between a single celled protoctist and a prokaryote

Many protists are pathogenic parasites that must infect other organisms to survive and propagate. Protist parasites include the causative agents of malaria, African sleeping sickness, and waterborne gastroenteritis in humans. Other protist pathogens prey on plants, effecting massive destruction of food crops. Members of the genus Plasmodium must infect a mosquito and a vertebrate to complete their life cycle.

In vertebrates, the parasite develops in liver cells and goes on to infect red blood cells, bursting from and destroying the blood cells with each asexual replication cycle [Figure 4].

Of the four Plasmodium species known to infect humans, P. In , it was estimated that malaria caused between 0. During the course of malaria, P. In response to waste products released as the parasites burst from infected blood cells, the host immune system mounts a massive inflammatory response with delirium-inducing fever episodes, as parasites destroy red blood cells, spilling parasite waste into the blood stream. Techniques to kill, sterilize, or avoid exposure to this highly aggressive mosquito species are crucial to malaria control.

This movie depicts the pathogenesis of Plasmodium falciparum , the causative agent of malaria. The glycoproteins are identified by the immune system as foreign matter, and a specific antibody defense is mounted against the parasite.

However, T. In this way, T. Without treatment, African sleeping sickness leads invariably to death because of damage it does to the nervous system. During epidemic periods, mortality from the disease can be high. Greater surveillance and control measures have led to a reduction in reported cases; some of the lowest numbers reported in 50 years fewer than 10, cases in all of sub-Saharan Africa have happened since In Latin America, another species in the genus, T.

The parasite inhabits heart and digestive system tissues in the chronic phase of infection, leading to malnutrition and heart failure caused by abnormal heart rhythms. An estimated 10 million people are infected with Chagas disease, which caused 10, deaths in Protist parasites of terrestrial plants include agents that destroy food crops. The oomycete Plasmopara viticola parasitizes grape plants, causing a disease called downy mildew [Figure 6] a. Grape plants infected with P.

The spread of downy mildew caused the near collapse of the French wine industry in the nineteenth century. Phytophthora infestans is an oomycete responsible for potato late blight, which causes potato stalks and stems to decay into black slime [Figure 6] b. Widespread potato blight caused by P. Late blight continues to plague potato crops in certain parts of the United States and Russia, wiping out as much as 70 percent of crops when no pesticides are applied.

They are equally important on the other end of food webs as decomposers. Protists are essential sources of nutrition for many other organisms. In some cases, as in plankton, protists are consumed directly. Alternatively, photosynthetic protists serve as producers of nutrition for other organisms by carbon fixation. For instance, photosynthetic dinoflagellates called zooxanthellae pass on most of their energy to the coral polyps that house them [Figure 7].

In this mutually beneficial relationship, the polyps provide a protective environment and nutrients for the zooxanthellae. The polyps secrete the calcium carbonate that builds coral reefs. Without dinoflagellate symbionts, corals lose algal pigments in a process called coral bleaching, and they eventually die.

This explains why reef-building corals do not reside in waters deeper than 20 meters: Not enough light reaches those depths for dinoflagellates to photosynthesize. Protists themselves and their products of photosynthesis are essential—directly or indirectly—to the survival of organisms ranging from bacteria to mammals.

On land, terrestrial plants serve as primary producers. Protists do not create food sources only for sea-dwelling organisms. They use an organelle called the hydrogenosome which is a greatly modified version of mitochondria for some of their energy production. For example, the sexually transmitted parasite Trichomonas vaginalis , which infects the human vagina and causes trichomoniasis , contains hydrogenosomes.

Protists gain nutrition in a number of ways. According to Simpson, protists can be photosynthetic or heterotrophs organisms that seek outside sources of food in the form of organic material. In turn, heterotrophic protists fall into two categories: phagotrophs and osmotrophs. Phagotrophs use their cell body to surround and swallow up food, often other cells, while osmotrophs absorb nutrients from the surrounding environment.

They have their own plastids, but will also happily eat other organisms. Most protists reproduce primarily through asexual mechanisms according to Simpson.

This can include binary fission, where a parent cell splits into two identical cells or multiple fission, where the parent cell gives rise to multiple identical cells. Simpson added that most protists probably also have some kind of sexual cycle, however, this is only well documented in some groups.

The classification history of protists traces our understanding of these diverse organisms. Often complex, the long history of protist classification introduced two terms, still used today, into the scientific lexicon: protozoa and protists. However, the meaning of these terms has also evolved over time. The observable living world was once neatly divided between plants and animals.

But the discovery of various microscopic organisms including what we now know as protists and bacteria brought forth the need to understand what they were, and where they fit taxonomically.

The first instinct of scientists was to relate these organisms to plants and animals by relying on morphological characteristics. The term protozoan plural: protozoa or protozoans , meaning "early animals," was introduced in by naturalist Georg A. Goldfuss, according to a article published in the journal International Microbiology. This term was used to describe a collection of organisms including ciliates and corals. By , Protozoa was established as a phylum or subset of the animal kingdom by German scientist Carl Theodor von Seibold.

This phylum included certain ciliates and amoebas, which were described by von Seibold as single-celled animals. In , the concept of protozoans was further refined and they were elevated to the level of a taxonomic kingdom by paleontologist Richard Owen. The members of this Kingdom Protozoa, in Owen's view, had characteristics common to both plants and animals. Though the scientific rationale behind each of these classifications implied that protozoans were rudimentary versions of plants and animals, there was no scientific evidence of the evolutionary relationships between these organisms International Microbiology, 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, Other protists are responsible for a range of serious human diseases, such as malaria and sleeping sickness.

The term protista was first used by Ernst Haeckel in Protists were traditionally placed into one of several groups based on similarities to a plant, animal, or fungus: the animal-like protozoa , the plant-like protophyta mostly algae , and the fungus-like slime molds and water molds. These traditional subdivisions, which were largely based on non-scientific characteristics, have been replaced by classifications based on phylogenetics evolutionary relatedness among organisms.

However, the older terms are still used as informal names to describe the general characteristics of various protists. Protists range from single-celled amoebas to multicellular seaweed. Protists may be similar to animals, plants, or fungi. Prokaryote or eukaryote? Kingdom Protista Protists are a group of all the eukaryotes that are not fungi, animals, or plants.

Summary Kingdom Protista includes all eukaryotes that are not animals, plants, or fungi.