Parasites live in or on an organism and harm the organism. A significant number of 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 colonize both 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 [link]. Of the four Plasmodium species known to infect humans, P. In , it was estimated that malaria caused between one-half and one million deaths, mostly in African children. 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 episodes of delirium-inducing fever as parasites lyse red blood cells, spilling parasite waste into the bloodstream.
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. Trypanosoma brucei , the parasite that is responsible for African sleeping sickness, confounds the human immune system by changing its thick layer of surface glycoproteins with each infectious cycle [link].
The glycoproteins are identified by the immune system as foreign antigens, and a specific antibody defense is mounted against the parasite. However, T. In this way, T. Without treatment, T. During epidemic periods, mortality from the disease can be high.
Greater surveillance and control measures lead 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 This movie discusses the pathogenesis of Trypanosoma brucei , the causative agent of African sleeping sickness. After about 10 weeks, individuals enter the chronic phase but most never develop further symptoms.
In about 30 percent of cases, however, the trypanosome causes further damage, especially to the heart and digestive system tissues in the chronic phase of infection, leading to malnutrition and heart failure due to abnormal heart rhythms.
An estimated 10 million people are infected with Chagas disease, and it caused 10, deaths in Plant Parasites 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. Grape plants infected with P. The spread of downy mildew nearly collapsed 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.
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. The fungus-like protist saprobes are specialized to absorb nutrients from nonliving organic matter, such as dead organisms or their wastes. For instance, many types of oomycetes grow on dead animals or algae. Saprobic protists have the essential function of returning inorganic nutrients to the soil and water.
This process allows for new plant growth, which in turn generates sustenance for other organisms along the food chain. Protists function at several levels of the ecological food web: as primary producers, as direct food sources, and as decomposers.
In addition, many protists are parasites of plants and animals and can cause deadly human diseases or destroy valuable crops. Which parasitic protist evades the host immune system by altering its surface proteins with each generation? Which of the following is not a way that protists contribute to the food web? How does killing Anopheles mosquitoes affect the Plasmodium protists?
Plasmodium parasites infect humans and cause malaria. However, they must complete part of their life cycle within Anopheles mosquitoes, and they can only infect humans via the bite wound of a mosquito. If the mosquito population is decreased, then fewer Plasmodium would be able to develop and infect humans, thereby reducing the incidence of human infections with this parasite.
Without treatment, why does African sleeping sickness invariably lead to death? The trypanosomes that cause this disease are capable of expressing a glycoprotein coat with a different molecular structure with each generation. Because the immune system must respond to specific antigens to raise a meaningful defense, the changing nature of trypanosome antigens prevents the immune system from ever clearing this infection.
Massive trypanosome infection eventually leads to host organ failure and death. Describe how increasing stress to the ocean would affect a food chain containing zooxanthellae, corals, parrotfish, and sharks. Protistan bacterivores can function largely as decomposers and efficient nutrient remineralizers. Some of the fixed organic carbon can be converted into larger microorganisms that may be consumed by larger metazoans and zooplankton.
Under many conditions, however, the microbial loop functions as both a carbon and nutrient sink by which organic matter is respired. This appreciable organic matter is not directly available to higher animals and the nutrients are recycled without ever entering a metazoan gut. The bottom line is that in addition to their significant contributions to biodiversity, the protists are major decomposers and mediators of nutrient recycling in ecosystems.
What a fantastic opportunity for young biologists to make significant contributions to our understanding of the operation of ecosystems!! Were I starting over, I would devote my career to this area, to help fill one of the most important voids in contemporary understanding of the bio sphere. Corliss J. Have the Protozoa been overlooked?. BioScience 51 : — Google Scholar. Foissner W. Soil protozoa: Fundamental problems, ecological significance, adaptations in ciliates and testaceans, bioindicators, and guide to the literature.
Progress in Protistology 2 : 69 — Wetzel R. It turns out that protists from each of these groups are important to life on Earth. Humans use protists for many other reasons: 1. Many protists are likewise normally utilized as a part of restorative research. For instance, prescriptions produced using protists are utilized as a part of treatment of hypertension, assimilation issues, ulcers, and joint pain.
Other protists are used in scientific studies.
0コメント