Kingdom Protista is a diverse group of eukaryotic organisms. Protists are unicellular, some are colonial or multicellular, they do not have specialized tissue organization. The simple cellular organization distinguishes the protists from other eukaryotes. The cell body of the protists contain have a nucleus which is well defined and membrane bound organelles. Some have flagella or cilia for locomotion. Reproduction in protists is both asexual and sexual. They live in any environment that contains water.
General characteristics of Kingdom Protista are as follows:
- They are simple eukaryotic organisms.
- Most of the organisms are unicellular, some are colonial and some are multicellular like algae.
- Most of the protists live in water, some in moist soil or even the body of human and plants.
- These organisms are eukaryotic, since they have a membrane bound nucleus and endomembrane systems.
- They have mitochondria for cellular respiration and some have chloroplasts for photosynthesis.
- Nuclei of protists contain multiple DNA strands, the number of nucleotides are significantly less than complex eukaryotes.
- Movement is often by flagella or cilia.
- Protists are multicellular organisms, they are not a plant, animal or fungus.
- Respiration - cellular respiration is primarily aerobic process, but some living in mud below ponds or in digestive tracts of animals ares strict facultative anaerobes.
- Nutrition - they can be both hetreotrophic or autotrophic.
- Flagellates are filter feeding, some protists feed by the process of endocytosis (formation of food vacuole by engulfing a bacteria and extending their cell membrane).
- Reproduction - some species have complex life cycle involving multiple organisms. Example: Plasmodium. Some reproduce sexually and others asexually.
- They can reproduce by mitosis and some are capable of meiosis for sexual reproduction.
- They form cysts in adverse conditions.
- Some protists are pathogens of both animals and plants. Example: Plasmodium falciparum causes malaria in humans.
- Protists are major component of plankton.
Kingdom Protista are categorized into two taxons:
Protozoans - animal-like single-celled organisms.
Algae - plant-like single or multi-celled organisms.
Animal-like Protists - PROTOZOANS
Protists that have resemblance to animals are known as protozoans. They in moist and watery enviroments. The characteristics similar to animals are - their ability to move and their inability to produce their own food (heterotrophs). They differ from animals being unicellular while animals are multicellular.
Protozoans are classified on the way they move into four categories:
Sacordinians - move using pseudopod.
Zooflagellates - move using flagella.
Ciliaphorans - move using cilia.
Sporozoans - forms spores.
Phylum Sarcodina - The movement in sarcodinians is by extending lobes of cytoplasm known as pseudopodia. The pseudopoda is used for movement and feeding. During the formation of the pseudopodia the cytoplasm streams into the lobe causing the lobe to 'ooze' and grow. Because of this the peudopodians have a 'blob like appearance. Example: Amoeba, Foraminiferans.
Phylum Mastigophora (Zooflagellata) - These protozoans move with the help of flagella. Most of them are parasitic. Many flagellates are seen in the intestine of humans, in termites and other animals, some flagellates are harmful. Example: Trypanosoma gambiense causes sleeping sickness in cattle and human.
Phylum Ciliophora (Ciliates) - Protozoans of this phylum move with hair like structures called cilia. The cilia stick out of their cells. The movement of cilia is paddle like, it sways back and forth for movement and fast beating of the cilia causes movement of the organism. The cilia is also used to sweep food particles into the organism. Example: Paramecium - It is a ciliate protozoan found in fresh water and ponds. It commonly known as the slipper animal-cule.
Phylum Sporozoa - All members of this phylum are non-motile and parasitic. They forms spores and hence the name sporozoa. They lack locomotory structures and they are carried in their hosts by their body fluids. Many sporozoans causes serious diseases in humans. Example: Plasmodium - this parasite causes malaria in humans.
Plant-like Protists - ALGAE
Plant-like protists have chlorophyll like that in plants. The green substance in their cells enable them to make food bu photosynthesis. They produce and release oxygen like the plants. It is believed to be the most supply of oxygen on Earth is from the plant-like protists. The plant-like protists are the major food source and primary producers for water organisms.
Phylum Chlorophyta (Green Algae) - The green algae include unicellular and multicellular algae. They are mostly fresh water. Body is sheet-like thallus. They have cell walls made of cellulose and pectin. Food is reserve starch which is stored in pyrenoids. Example: Spirogyra - it is a unicellular green alga, it grows as a green thread or filament.
Phylum Rhodophyta (Red Algae) - Red algae are mostly large and multicellular. They grow in oceans. The algae 'Nori' and Gelidium are used as food, in parts of Asia. Carragean and agar are glue-like substances in red-a;gae. Agar is used as a medium used for growing bacteria and other organisms under laboratory conditions. Agar is also used to make gelatin capsules. and a base for cosmetics. Carragean is used as a stabilizer and thickener in dairy products. It is also used to give toothpaste its creamy texture.
Phylum Phaeophyta (Brown Algae) - Brown algae are multicellular. They grow on rocks in shallow water of the sea. Large brown algae are called kelps. Kelps may grow densely in the sea and form kelp forests. They form important food sources for fish and invertebrates. The brown algae growing on rocks are known as rockweed. Example of rockweed is Sargassum. Algin is a substance derived from some algae which is used in making ice cream, lotion and plastics.
Phylum Chrysophyta (Golden algae) - 'Chryso' means 'color of gold'. There are three types of golden-algae: yellow-green algae, golden brown algae, diatoms. Diatoms are the most abundant and are found in seawater and freshwater habitats. The shell of diatoms are made of silica. They are major source of food to may aquatic organisms. The shells of fossil diatoms form thick deposits on the sea floor known as 'diatomaceous earth'. It is used as water filters, abrasive and to add sparkling to products such as paint and fingernail polish.
Phylum Pyrrophyta (Fire Algae) - It contains of species of one-celled algae called dinoflagellate which means 'spinning swimmers'. They store food in the form of starch and oils. The red color is due to chlorophyll a and c and xanthophylls. These organisms have ability of bioluminescence. Almost all species like in marine water. Some species causes the 'red tide phenomenon'. The dinoflagellates causing red tides are known as Gonyaulax, which contain a neurotoxin and are poisonous to marine fauna.
Fungus-like ProtistsSlime Molds
- Slime molds are saprophytic protists. They are very bright in appearance. They live in moist soil, decaying plants and trees. They are single-celled organisms. During favorable condition they form multicellular aggregations called plasmodium. During unfavorable conditions, plasmodia differentiate to form fruiting bodies bearing spores at the tip. These spores posses resistant true walls, which help in survival for a long time during adverse conditions. These spores disperse by air currents.
Few well known examples are follows:
Green algae - Spirogyra, Ulva, Chlamydomonas, Volvox.
Red algae - Porphyra, Rotalgen.
Brown algae - Laminaria, Nereocystis.
Water molds - Saprolegnia.
Phylum Ciliata - Paramecium, Vorticella.
Phylum Dinoflagellata - Ceratium, Gonyaulax.
Phylum Mastigophora - Trypanosoma, Trichonympha.
Phylum Sarcodina - Amoeba.
Economic Importance of Protists
Protists are useful in the following manners:Source of food
- Some protists like kelps are edible.Source of commercial products
- Marine protists are source of useful substances like algin, agar, carragean and antiseptics.Primary producer of aquatic ecosystem
- Many protists are primary producers, they play a basic role in food cahins, providing food and oxygen.Source of medicines
- Sodium laminaria sulphate, Fucoidin, Heparin are algal products used as blood coagulants. Lyngbya produces an anti-cancer compound. Source of mineral
- Kelps are rich in sodium, potassium, iodine etc, they are good source of minerals. Biological research
- They are used in biological research, e.g., Chlorella is unicellular, non-motile alga.Pathogens
- Thhese ar pathogenic organisms and may cause many disease in man and also in fruits and vegetables it causes late blight potatoes and causes disease in some fishes.