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Kingdom Protista: Its Characteristics, History and Classifications
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Protista are group of comparative simple organisms that belong to Kingdom Protoctista with both characteristics of both plants and animals and commonly known as “protist”. Protists are single-celled organism that can only be seen by a microscope though some protist contains more than one cell. They can live in different environment like freshwater, saltwater, soil, moist surfaces and even in the intestinal tract of animals that can cause vile digestive processes.
Protist can manufacture their own food just like plants and can also move around under their own power just like animals. Although, they don’t have cells organized to for specialized tissues. Some familiar protists are:
- Slime Molds
It was also believed that the members of Kingdom Protista gave rise to the Kingdom Fungi, Plantae and Animalia about 600 million years ago. Protists are considered all “eukaryotes” organisms which mean their cells have a nucleus which is a membrane-bounded structure that covers the cell’s genetic material. They are free-living organism. Protist that lives inside or outside an organism’s body that causes harm are called parasites. There are two types of parasitic protists:
- Ectoparasites – parasitic protist that lives only outside or in the surface host’s body.
- Endoparasites - parasitic protist that lives inside the host’s body mostly in food-tube or even in blood.
Protists are enormous in number. Like for example:
- A pond may contain billions of free-living protist
- A human body hosts may contain a large number of parasitic protist
Kingdom Protist includes three (3) big groups of organisms:
- Eukaryotic algae
- Fungus-like slime mold
Protozoans consist of four major groups:
Brief History of Protist
In 1976, Antoni van Leeuwenhoek a Dutch naturalist and also the inventor of the microscope has first made a detailed description about protest. He observed a microscopic organism moving and since all organisms are traditionally considered animals before he then called it “animalcules”.
In 1862, Ernst Haeckel a German biologist first used the term “protista” to describe microscopic organisms that show both characteristic of plants and animals, that these organisms are motile and photosynthetic. After Haeckel, scientist informally identified three kingdoms:
- Kingdom Plantae – includes all plants capable for making foods
- Kingdom Animalia – includes all animals
- Kingdom Protista – includes all microbes
In 1930s, scientist formally suggested that unicellular organisms, including bacteria must be put in their own kingdom – Kingdom Protista.
In 1959, R. H. Whittaker an American biologist illustrated a classification of a system of five (5) principal kingdoms:
- Kingdom Plantae
- Kingdom Animalia
- Kingdom Protista
- Kingdom Fungi
- Kingdom Bacteria
Four (4) Major Groups of Protozoan’s
Flagellates are single-celled organisms in the Subphylum Mastigophora with whip-like projections called “flagella” which they use for their movements. They can live as unicellular, in colonies or as parasites. Flagellates have approximately 2,000 species and most of them are free-living organisms. Some examples of these include:
Ciliates are a common name for higher protist that belongs to Phylum Ciliophora with almost 7000 known species that ranges from 10 micrometers to 2 millimeters in size. The name comes from the Latin word “Cilium” which means “eyelid” and Greek word “Phoros” which means “bearing”. Ciliates are unicellular organism that exhibit different shapes and arrangement of hair-like structure called “cilia” and contain two nuclei in their single cell. Some examples of ciliates are:
They can be found in all water environments and characterized by a mouth-like cytostome which is an area of the cell for gulping food. Most of ciliates show commensalism relationship to their host. They are food sharers for herbivores and parasites in human intestines that can cause inflammation (balantidiasis). Ciliates are divided into four groups:
- Holotricha - free swimming organism.
- Suctoria – have tentacles instead of cilia as adult and attached to substrate
- Peritricha – are bell-shaped organisms and are often colonial
- Spirotricha – are trumpet-shaped stentor and in Genera Euplotes which have fused cilia that serves as legs.
Sarcodina is the subphylum of (Phylum Sarcomastigophora) of single-celled organisms that move by protoplasmic flow. The name comes from the Greek term “Sarx” which means “flesh” and “Eidos” which means “form” with approximately about 8000 species. Certain sarcodine species have protoplasmic extension called “pseudopodia” which means “false feet” that are used for their movement (locomotion) and feeding. Most of them are free-living organisms in freshwater and in seawater. The subphylum includes:
- Foraminifera (shell secreting)
- Radiolaria (shell secreting)
Subphylum Sarcodina is sometimes subdivided into two classes:
- Rhizopoda (litterally “root-footed”)
- Actinopoda (literally “ray-footed”).
Sporozoans are unicellular animal-like organisms and often form colonies. They do not have differentiation in tissue system. They contain “spores” which is a specialized cell for production that is commonly known as “gamete or sex cell”.
Most of Sporozoans are found in aquatic habitats such as lakes, sea, oceans, rivers and ponds. They have different length that ranges from 2-17 micrometers. They obtain food by engulfing bacteria, waste products, algae and even other protozoa. Most species of Sporozoans are moving either via whip-like structure called flagella, hair-like structure called “cilia” or by amoeboid motion or foot-like extension called “pseudopods”.
All Sporozoans are vile parasites of animals. They can transfer and move from one host to another in the spore stage. Because their spores are light and small, they can be easily diffused by wind, water and other agents from one host to another. Some harmful Sporozoans are:
- Plasmodium vivax, P. falcifarum
- P. ovale
References ; Wikipedia, the free encyclopedia , Science and Technology by Lilia M. Rabago Ph. D , Crescensia C. Joaquin Ph.D, Catherine B. Lagunzad , PH. D, Encarta