can anyone tell me about protista briefly...........

Protista

Some members of Kingdom Protista are unicellular, others are colonial, and yet others are multicellular. Note that in the colonial forms, all the cells are similar with similar, generalized functions, whereas in the truly multicellular species, the “body” of the organism consists of a variety of types of cells, each type with its own specialized function. These organisms are all eukaryotes (they have a true nucleus). They all need some kind of a water-based environment--which can be fresh or marine water, snow, damp soil, polar bear hairs--in which to live. All are aerobic and have mitochondria to do cellular respiration, and some have chloroplasts and can do photosynthesis. Most of them reproduce or grow by mitosis, and some reproduce by meiosis and fertilization. Many can form cysts in adverse conditions. Protists are a major component of plankton.

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Protists are a diverse group of eukaryotic microorganisms.

The protists do not have much in common besides a relatively simple organization —either they are unicellular, or they are multicellular without specialized tissues. This simple cellular organization distinguishes the protists from other eukaryotes, such as fungi, animals and plants.

Protists live in almost any environment that contains liquid water. Many protists, such as the algae, are photosynthetic and are vital primary producers in ecosystems, particularly in the ocean as part of the plankton. Other protists, such as the Kinetoplastids and Apicomplexa, are responsible for a range of serious human diseases, such as malaria and sleeping sickness.

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What are protistas? Prostista is a kingdom, to which the eukaryotic microorganisms, protists belong. Protista was first observed as primitive unicellular forms of both plants and animals, as observed by scientist John Hogg, in 1860s. At that time, this kingdom was known as "Protoctista", that literally meant first established beings. Later in the year 1866, the term protista was coined by Ernst Haeckel. This kingdom belongs to the domain Eykarya. Recent classifications are being made by scientists where listing of organisms is done on hierarchical basis. They have different characteristics that distinguish them from other kingdoms. The most common protista examples include, amoeba, plasmodium, pararamecium, slime mold, red, brown and golden algae, fungi, diatoms, etc. To know in details about protista, reda this article protista - characteristics.

General Protista Characteristics

  • They are mostly unicellular but some can be multicellular or colonial organisms also.
  • They can be free living or parasites.
  • They have aerobic mode of respiration and have mitochondria for cellular respiration.
  • They are true eukaryotes and are nucleated.
  • They have (9+2) arrangement of flagella and have membranous organelles.
  • They can reproduce sexually (syngamy) or asexually
  • They are grouped into 3 categories: animal like (protozoa), fungus like and plant-like.
  • According to the categories, they have different modes of nutrition, like heterotrophy or autotropohy.
  • Plant-like protists (algae) have chlorophyll and accessory pigments, like xanthophylls, phycobilins and carotene.

Classification of Protists - Based on Sub Groups

Characteristics of Plant Like: e.g Algae
 

thmbs up plzzzz

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Hi!

@Nivas: You may refer to the answer provided by your friends.

@Yashu, Akshita: Very good! Keep up the good work.

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 than u

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 thank u ......

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Protist
Temporal range: Neoproterozoic – Recent
Scientific classification
Domain:Eukarya
Kingdom:Protista*
Haeckel, 1866
Typical phyla

Protists (pronounced /ˈproʊtɨst/) are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy.[1] Instead, it is "better regarded as a loose grouping of 30 or 40 disparate phyla with diverse combinations of trophic modes, mechanisms of motility, cell coverings and life cycles."[2]

The protists do not have much in common besides a relatively simple organization[3]—either they are unicellular, or they are multicellular without specialized tissues. This simple cellular organization distinguishes the protists from other eukaryotes, such as fungi, animals and plants.

The term protista was first used by Ernst Haeckel in 1866. Protists were traditionally subdivided into several groups based on similarities to the "higher" kingdoms: the unicellular "animal-like" protozoa, the "plant-like" protophyta (mostly unicellular algae), and the "fungus-like" slime molds and water molds. These traditional subdivisions, largely based on superficial commonalities, 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 morphology and ecology of various protists.

Protists live in almost any environment that contains liquid water. Many protists, such as the algae, are photosynthetic and are vital primary producers in ecosystems, particularly in the ocean as part of the plankton. Other protists, such as the Kinetoplastids and Apicomplexa, are responsible for a range of serious human diseases, such as malaria and sleeping sickness.

Contents

Classification

Historical classifications

The first division of the protists from other organisms came in the 1830s, when the German biologist Georg August Goldfuss introduced the word protozoa to refer to organisms such as ciliates and corals.[4] This group was expanded in 1845 to include all "unicellular animals", such as Foraminifera and amoebae. The formal taxonomic category Protoctista was first proposed in the early 1860s by John Hogg, who argued that the protists should include what he saw as primitive unicellular forms of both plants and animals. He defined the Protoctista as a "fourth kingdom of nature", in addition to the then-traditional kingdoms of plants, animals and minerals.[4] The kingdom of minerals was later removed from taxonomy by Ernst Haeckel, leaving plants, animals, and the protists as a “kingdom of primitive forms”.[5]

Herbert Copeland resurrected Hogg's label almost a century later, arguing that "Protoctista" literally meant "first established beings", Copeland complained that Haeckel's term protista included anucleated microbes such as bacteria. Copeland's use of the term protoctista did not. In contrast, Copeland's term included nucleated eukaryotes such as diatoms, green algae and fungi.[6] This classification was the basis for Whittaker's later definition of Fungi, Animalia, Plantae and Protista as the four kingdoms of life.[7] The kingdom Protista was later modified to separate prokaryotes into the separate kingdom of Monera, leaving the protists as a group of eukaryotic microorganisms.[8] These five kingdoms remained the accepted classification until the development of molecular phylogenetics in the late 20th century, when it became apparent that neither protists nor monera were single groups of related organisms (they were not monophyletic groups).[9]

Modern classifications

Currently, the term protist is used to refer to unicellular eukaryotes that either exist as independent cells, or if they occur in colonies, do not show differentiation into tissues.[10] The term protozoa is used to refer to heterotrophic species of protists that do not form filaments. These terms are not used in current taxonomy, and are retained only as convenient ways to refer to these organisms.

The taxonomy of protists is still changing. Newer classifications attempt to present monophyletic groups based on ultrastructure, biochemistry, and genetics. Because the protists as a whole are paraphyletic, such systems often split up or abandon the kingdom, instead treating the protist groups as separate lines of eukaryotes. The recent scheme by Adl et al. (2005)[10] is an example that does not bother with formal ranks (phylum, class, etc.) and instead lists organisms in hierarchical lists. This is intended to make the classification more stable in the long term and easier to update. Some of the main groups of protists, which may be treated as phyla, are listed in the taxobox at right.[11] Many are thought to be monophyletic, though there is still uncertainty. For instance, the excavates are probably not monophyletic and the chromalveolates are probably only monophyletic if the haptophytes and cryptomonads are excluded.[12]

Metabolism

Nutrition in some different types of protists is variable. In flagellates, for example, filter feeding may sometimes occur where the flagella find the prey. Other protists can engulf bacteria and digest them internally, by extending their cell membrane around the food material to form a food vacuole. This is then taken into the cell via endocytosis (usually phagocytosis; sometimes pinocytosis).


 

Nutritional types in protist metabolism
Nutritional typeSource of energySource of carbonExamples
 Phototrophs  Sunlight  Organic compounds or carbon fixation Algae, Dinoflagellates or Euglena 
 Organotrophs Organic compounds  Organic compounds  Apicomplexa, Trypanosomes or Amoebae 

Reproduction

Some protists reproduce sexually (gametes), while others reproduce asexually (binary fission).

Some species, for example Plasmodium falciparum, have extremely complex life cycles that involve multiple forms of the organism, some of which reproduce sexually and others asexually.[13] However, it is unclear how frequently sexual reproduction causes genetic exchange between different strains of Plasmodium in nature and most populations of parasitic protists may be clonal lines that rarely exchange genes with other members of their species.[14]

Role as pathogens

Some protists are significant pathogens of both animals and plants; for example Plasmodium falciparum, which causes malaria in humans, and Phytophthora infestans, which causes late blight in potatoes.[15] A more thorough understanding of protist biology may allow these diseases to be treated more efficiently.

Researchers from the Agricultural Research Service are taking advantage of protists as pathogens in an effort to control red imported fire ant (Solenopsis invicta) populations in Argentina. With the help of spore-producing protists such as Kneallhazia solenopsae the red fire ant populations can be reduced by 53-100%.[16] Researchers have also found a way to infect phorid flies with the protist without harming the flies. This is important because the flies act as a vector to infect the red fire ant population with the pathogenic protist.[17]

 

 

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 thank you sir

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