Other protists, such at amoebae, form cytoplasmic extensions called pseudopodia anywhere on the cell, anchor the pseudopodia to a surface, and pull themselves forward. Some protists can move toward or away from a stimulus; a movement referred to as taxis. Protists accomplish phototaxis, movement toward light, by coupling their locomotion strategy with a light-sensing organ.
Different types of motility in protists : Protists use various methods for transportation. Protists live in a wide variety of habitats, including most bodies of water, as parasites in both plants and animals, and on dead organisms. Protist life cycles range from simple to extremely elaborate. Certain parasitic protists have complicated life cycles and must infect different host species at different developmental stages to complete their life cycle.
Some protists are unicellular in the haploid form and multicellular in the diploid form, which is a strategy also employed by animals. Other protists have multicellular stages in both haploid and diploid forms, a strategy called alternation of generations that is also used by plants. The slime molds are categorized on the basis of their life cycles into plasmodial or cellular types. Plasmodial slime molds are composed of large, multinucleate cells and move along surfaces like an amorphous blob of slime during their feeding stage.
The slime mold glides along, lifting and engulfing food particles, especially bacteria. Upon maturation, the plasmodium takes on a net-like appearance with the ability to form fruiting bodies, or sporangia, during times of stress. Meiosis produces haploid spores within the sporangia. Spores disseminate through the air or water to potentially land in more favorable environments.
If this occurs, the spores germinate to form amoeboid or flagellate haploid cells that can combine with each other and produce a diploid zygotic slime mold to complete the life cycle. Plasmodial slime mold life cycle : Haploid spores develop into amoeboid or flagellated forms, which are then fertilized to form a diploid, multinucleate mass called a plasmodium. This plasmodium is net-like and, upon maturation, forms a sporangium on top of a stalk.
The sporangium forms haploid spores through meiosis, after which the spores disseminate, germinate, and begin the life cycle anew.
Some amoeba-like protists, though, are opportunistic pathogens. Given the opportunity, they may live as a parasite inside a host and cause disease. One of the medically-important amoebas is the Entamoeba histolytica.
This species causes entamoebiasis and amebic dysentery to its human and other primate hosts. It forms a cyst that can be transmitted through ingestion of infected water or food. When swallowed, the cyst will release the trophozoite in the digestive tract and become pathogenic. It causes flask-shaped ulcers, and eventually, bloody diarrhea. In certain instances, it migrates to the bloodstream, and subsequently, reaches other organs e.
Another is the brain-eating amoeba, Naegleria fowleri. The species lives in hot springs, warm freshwater lakes, and rivers. It can turn from a free-living state into a parasite when it enters the body of a host, e.
It enters through the nose and penetrates the nasal mucosa. Later, it migrates to the brain through the olfactory nerves. In the brain, it feeds on brain tissues, e. The nucleus containing the genetic material, DNA, and the mitochondria, well-identified as the "powerhouse of the cell", came about.
This tutorial speaks of the evolution of organelles, their diversity, and similarity Read More. It only takes one biological cell to create an organism. A single cell is able to keep itself functional through its 'miniature machines' known as organelles. Read this tutorial to become familiar with the different cell structures and their functions Organisms employ different strategies to boost its defenses against antigens.
Humans have an immune system to combat pathogens. Read this tutorial to learn the first and second lines of defense that the human body employs. Amoeboid protists and some parasitic lineages that lack mitochondria are part of Amoebozoa. Heterotrophic protists — organisms that take in nutrients from other organisms — are part of Excavata, while plants and most other photosynthetic organisms are part of Archaeplastida, according to the Encyclopedia of Evolutionary Biology.
In addition, he noted that amoebas are also present within Rhizaria, Excavata, Opisthokonta for example, Nucleariids, which have filopodia and within the Stramenopiles for example, Labyrinthulids. Amoebas are known to cause a range of human diseases.
Amebiasis, or amoebic dysentery, is an infection caused by Entamoeba histolytica, a human intestinal parasite, according to the Centers for Disease Control and Prevention CDC. According to the National Institutes of Health NIH , Entamoeba histolytica can invade the colon wall and cause colitis, or can cause severe diarrhea and dysentery.
Though the disease can occur anywhere in the world, it is most common in tropical regions that have substandard sanitation and crowded conditions. Contact lens wearers are potentially at risk of a rare infection of the cornea called Acanthamoeba keratitis. According to the CDC , species in the Acanthamoeba genus are free-living and are commonly found in soil, air and water.
Poor contact lens hygiene practices, such as improper storage, handling and disinfection or swimming with lenses, are some of the risk factors for the disease.
While the initial symptoms include redness, itchiness and blurred vision, if left untreated the infection will eventually lead to severe pain and can lead to the loss of vision, according to the CDC. Amoebas also cause different infections of the brain. Naegleria fowleri , which has been dubbed "the brain-eating amoeba," causes primary amoebic meningoencephalitis PAM. Though the disease is rare, it is almost always fatal , according to the CDC. Early symptoms include fever and vomiting, ultimately progressing to more severe symptoms such as hallucinations and coma.
Naegleria fowleri is present in warm freshwater bodies such as hot springs, lakes and rivers, or in poorly chlorinated swimming pools and contaminated, hot tap water. These amoebas enter from the nose and travel to the brain. Another amoeba, Balamuthia mandrillaris, can cause a brain infection known as granulomatous amoebic encephalitis GAE.
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. According to their recent malaria fact sheet , in there were an estimated , deaths due to malaria in the world, the majority of which 90 percent occurred in Africa.
Certain strides have been made in reducing the rates of incidence occurrence of new cases and mortality rates in part by supplying insecticide treated mosquito nets, spraying for mosquitoes and improving diagnostics. Between and the rate of incidence fell by 37 percent globally and mortality rates fell by 60 percent globally.
The WHO has a goal of eliminating malaria in at least 35 countries by Protists also play an important role in the environment. According to a review article published on the Encyclopedia of Life Sciences eLS website, nearly 50 percent of photosynthesis on Earth is carried out by algae. Protists act as decomposers and help in recycling nutrients through ecosystems, according to a review article published in the journal ACTA Protozoologica. In addition, protists in various aquatic environments, including the open water, waterworks and sewage disposal systems feed upon, and control bacterial populations ACTA Protozoologica, Credit: Monkey Business Images Shutterstock.
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