Protista, Chromista, Fungi
Eukaryotes - domain Eukaryota - are organisms whose cells have a nucleus enclosed within a nuclear envelope.
Protista (Empire Eukaryota)
A protist is any eukaryotic organism that is not an animal, land plant, or true fungus.
The primary feature of all protists is that they are eukaryotic organisms (with a membrane-enclosed nucleus and membrane-bound organelles). Most protist species are unicellular organisms that exist as independent cells or in colonies, but there are a few multicellular protists (e.g. kelp).
Memberst of Kingdom Protista are usually aquatic organisms, present in areas with moisture or in the soil. They may be autotrophic (can create their own food) or heterotrophic (has to derive nutrition from other organisms). Protista reproduces by asexual means. The sexual method of reproduction is extremely rare and occurs only during times of stress.
The taxonomy of protists is still changing.
Protists were traditionally subdivided into several groups based on superficial commonalities:
- Protozoa - unicellular "animal-like" (heterotrophic, and sometimes parasitic) organisms that are sub-divided by characteristics: (flagellated) Flagellata, the (ciliated) Ciliophora, the (phagocytic) amoeba, and the (spore-forming) Sporozoa.
- Protophyta - "plant-like" (autotrophic) organisms are composed mostly of unicellular algae.
- Molds - "fungus-like" slime molds and water molds.
Some protists, sometimes called ambiregnal protists, have been considered to be both protozoa and algae or fungi.
Chromista is a biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles. It includes all protists whose plastids contain chlorophyll c. Members range from marine algae, to potato blight, brain parasite (Toxoplasma), and malarial parasite (Plasmodium).
Chromista, unlike plants, have chlorophyll c, and do not store their energy in the form of starch. Photosynthetic chromists often carry various pigments in addition to chlorophyll that give them characteristic brown or golden color. Members range from marine algae, to potato blight, brain parasite (Toxoplasma), and malarial parasite (Plasmodium).
True fungi (Eumycota) include microorganisms such as yeasts, molds, and mushrooms, and have chitin in their cell walls.
Fungi are heterotrophs like animals: they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment. They are the principal decomposers in ecological systems. Fungi do not photosynthesize. They are usually noticeable when fruiting as mushrooms or molds.
Fungi have long been used as food: mushrooms, truffles, yeast (leavening agent for bread), and in the fermentation of wine, beer, soy sauce, etc. The fruiting structures of a few species contain psychotropic compounds. At least 300 fungi species can be pathogenic to humans, many produce mycotoxins that are toxic to all animals, including humans.
Since recently, fungi have been used for the production of antibiotics, enzymes, and detergents, as biological pesticides.
The mycorrhizal symbiosis existed at least 400 million years. Over 90% of all plant species are dependent upon relationship with fungi for survival. It often increases the plant's uptake of inorganic compounds, such as nitrate and phosphate from soils having low concentrations of these key plant nutrients. Common mycorrhizal networks can also mediate plant-to-plant transfer of carbohydrates and other nutrients. Endophytic colonization of plants by fungi may also benefit both symbionts. But over 8,000 species known to be detrimental to plants.
Little is known of the true biodiversity of fungi, which has been estimated at 2.2 - 3.8 million species (only about 148,000 have been described).
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