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general characteristics of kingdom protista

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Protista Protista

The Protista, or Protoctista, are a kingdom of simple eukaryotic organisms, usually composed of a single cell or a colony of similar cells. Protists live in water, in moist terrestrial habitats, and as parasites and other symbionts in the bodies of multicellular eukaroytes. Other eukaryotic kingdoms—the Plantae, Fungi, and Animalia—are each believed to be monophyletic . That is, all plants evolved from one ancestral plant, all animals from one ancestral animal, and all fungi from one ancestral fungus. The Protista, however, are not; they are almost certainly polyphyletic and did not arise from a single ancestral protist. Rather, the Protista are a category of miscellaneous eukaryotes, not closely related to each other and not sharing many characteristics, but not fitting any other kingdom of life. Some authorities divide the Protista into as many as twenty-seven phyla, and some feel the Protista should be discarded as a kingdom name, and these organisms divided into as many as twelve kingdoms. Historically, the Protista were divided into three main categories: the plantlike algae, animal-like protozoans, and funguslike slime molds. This classification persists in many elementary textbooks; however, current molecular evidence indicates that these are not natural groups related by common descent, but groups with merely superficial , deceptive similarities. Classifying them together is probably no more scientific than it would be to classify bees, birds, and bats in one group simply because they all have wings and fly. The two flagellated protozoan groups called trypanosomes and dinoflagellates, for example, are probably less related to each other than a human is to a fish. Genetic evidence (base sequences in their mitochondrial deoxyribonucleic acid [mtDNA] and ribosomal ribonucleic acid [rRNA]) now indicates that the following are more natural (evolutionarily related) groups of Protista. These are the most primitive protists. Some lack mitochondria and suggest what the first eukaryotes may have been like, while others have primitive mitochondria that closely resemble bacteria. Some basal Protista without mitochondria are Trichomonas, a vaginal parasite of humans; Giardia, an intestinal parasite; and Entamoeba, the cause of amoebic dysentery. The lack of mitochondria is not necessarily the primitive (original) condition of all these protists, however. Although Giardia lacks mitochondria, it does have mitochondrial genes. Apparently it once had mitochondria, and these genes transferred to its nuclear DNA before the mitochondria were lost. Basal Protista with mitochondria include Trypanosoma, a genus of blood parasites that cause African sleeping sickness and other diseases; Euglena, a green freshwater flagellated protozoan with chloroplasts; and Physarum, a common terrestrial slime mold. Alveolates are named for flattened sacs called alveoli just beneath their plasma membranes. They have mitochondria with tubular cristae rather than the flattened cristae typical of most mitochondria. Alveolates include dinoflagellates, aquatic forms with two flagella and a cell wall made of armorlike cellulose plates; Paramecium and other familiar ciliates; and the Apicomplexa, a group of intracellular parasites that includes Plasmodium, the cause of malaria, and Toxoplasma, the cause of toxoplasmosis. Stramenopiles include water molds, golden and brown algae, and diatoms. The funguslike water molds (oomycetes) live in fresh water and soil, feeding on living or decaying organisms. Despite their name, some of them are important pests of row crops, including potato blight, downy mildew, and white rust. The golden algae (Chrysophyta ) and brown algae (Phaeophyta ) include many familiar seaweeds easily found on rocky coasts. Kelp is a gigantic marine brown alga (Macrocystus ) that grows up to 30 meters (100 feet) long and forms dense "forests" in some coastal waters. Diatoms are microscopic unicellular algae encased in siliceous (glasslike) walls, often with delicate lacy designs like tiny jewel boxes or Christmas ornaments. The red algae (Rhodophyta ) include most seaweeds and are most abundant in tropical seas. Coral reefs are made not only by corals but also by coralline red algae that deposit calcium carbonate in the reef. Some red algae produce viscous polysaccharides such as agar and carrageenan, used to thicken ice cream, desserts, salad dressings, toothpaste, cosmetics, paints, and bacterial culture media. The green algae (Chlorophyta ) include the single-celled Chlamydomonas, the spherical colonies of Volvox, and large seaweeds such as Codium magnum. Some unicellular green algae, notably Chlorella, live within the cells of animals, imparting a green color to some sponges, hydras, and flatworms. The plant kingdom probably evolved from a green alga. Biologists in several subdisciplines of biology specialize in the Protista or have interests that overlap with this kingdom. Microbiologists study bacteria and some unicellular protists. Phycologists specialize in algae. Protozoologists study protozoans. Mycologists specialize in fungi but also often study water molds and slime molds, formerly classified as fungi. Parasitologists study disease-producing protists. see also Algae; Coral Reef; Fungi; Mitochondrion; Plant Pathogens and Pests; Protozoa; Protozoan Diseases; Slime Molds Kenneth S. Saladin Margulis, L., J. O. Corlis, M. Melkonian, and D. J. Chapman. Handbook of Protoctista, Boston: Jones & Bartlett, 1990. Margulis, L., and K. Schwartz. The Five Kingdoms, 3rd ed. New York: W. H. Freeman and Company, 1998. Patterson, D. J. "The Diversity of Eukaryotes." American Naturalist 154 (1999): S96–S124.


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Question:What's the number of cells, types of cells, distinguishing characteristics, modes of nutrition on reproduction? i also have a test on it tomorrow, ..thanks!

Answers:hello, your questions are all on my test that i am having tomorrow in biology. All of your questions are on a sheet i had to do as an assignment one day. 1. whats the number of cells? can be both unicellular or multicellular 2. what type of cells? eukaryotic 3. distinguishing characteristics? nothing because they are a varied group of organisms that cannot be classified into other kingdom. 4. modes of nutrition on reproduction? --i am sorry i am not sure of the answer to that last question. i hope that helps*

Question:1. How do you distinguish "animal" Protozoans from "plant" Protozoans? 2. Some botanists classify Euglenas as plants, some zoologists classify euglenas as animals. What are the reasons form placing Eugleas in both the plant and animal kingdoms? 3. What survial advantages does the process of ASEXUAL reproduction have for the Protists? 4. What evolutionary advantages does the SEXUAL reproduction have for Protists?

Answers:1. Some have characteristics associated with animals, like they consume food and can move. Others are more plant like. 2. Some have chloroplasts and thus are more like plants. Others feed by phagocytosis, which is more like an animal. 3. Only one cell is needed to reproduce. Can rapidly populate a given niche. 4. Leads to genetic diversity and increases the chances that some cells will survive some environmental change (temperature, humidity, food source, etc.).

Question:What do you think- should it: a. remain the same b. be joined with kingdoms Animalia, Fungi, and Plantae and the criteria of those kingdoms redefined c. Be split into three more new kingdoms? (Protozoa have their own kingdom, Algae their own, and fungus-like protists their own.) please only answer if you actually know what I mean.

Answers:I think it should remain the same. Formerly, we thought that organisms in Kingdom Protista are too simple to be classified among the other three kingdoms: Plantae, Animalia, and Fungi. We thought that if knowledge advances us more onto this field, no organism will be left in Kingdom Protista. But we no longer think so. Studying Kingdom Protista leads us to a better understanding of the organisms classified under them in general. We used to underestimate them; thinking they are unclassified organisms. But this is no longer the case. As I studied Kingdom Protista in my General Botany classes, it came to me that they are themselves diverse in their own way; not as plants, as animals, or as fungi. Rather, not only in my point of view but in most scientists' point of view as well, organisms in Kingdom Protista play an evolutionary role for the organisms in Kingdoms Plantae, Animalia, and Fungi. I would not prefer splitting them into three more kingdoms. It requires further knowledge about each of the organisms. Let us rely on the scientists for that.

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