The Protista kingdom is the most diverse of the five eukaryotic kingdoms. There are over 200,000 known species of protists, with many more yet to be discovered. Protists come in a myriad of colors, sizes, and shapes. They inhabit almost all areas where water occurs part or all of the time. They form the basis of ecosystems by producing food, as is the case with photosynthetic protists, or by being eaten by larger organisms. They range in size from microscopic single-celled organisms to giant algae that can grow up to 100 m in length.
German zoologist Ernst Haeckel (1834–1919) first proposed the kingdom of Protista in 1866. This early classification included all microorganisms that were not plants or animals. Biologists did not readily accept this realm, and even after American botanist Herbert F. Copeland tried again to establish its use 90 years later, there was not much support from the scientific community. Around 1960, R.Y. Stanier et al.CV of Neil(1897–1985) proposed the division of all organisms into two groups, prokaryotes andeukaryotes🇧🇷 Eukaryotes are organisms that have membrane-bound organelles in which metabolic processes take place, while prokaryotes lack these structures. In 1969, Robert Whittaker proposed the Five Kingdoms classification system. The Kingdom of Protista was one of five proposed kingdoms. At that time, only single-celled eukaryotic organisms were considered protists. Since then, the kingdom has expanded to include multicellular organisms, although biologists still disagree on what exactly makes an organism a protist.
Protists are difficult to characterize because of the great diversity of the kingdom. These organisms vary in body shape, diet, and reproduction. They can be unicellular, colonial or multicellular. Like eukaryotes, protists can have many different organelles, including aKern, mitochondria, contractile vacuoles, food vacuoles, eyespots, plastids, cuticles and flagella. They contain the nuclei of protists.chromosomes, SwindlerDNSassociated with proteins. Protists are also capable of having sex.asexual reproduction, meiosis and mitosis. Protists can live freely or in symbiosis with another organism. This symbiosis can be mutual, where both partners benefit, or it can be parasitic, where the protist uses its host as a source of food or shelter without bringing any benefit to the other organism. Many protists are economically important and useful to mankind, while others cause deadly diseases. Protists make up the majorityPlanktonin aquatic systems, where they serve as the basis forfood chain🇧🇷 Many protists are motile and use structures such as cilia, flagella, orpseudopods (false feet) to move, while others are sessile. They can be autotrophs, which make their own food from sunlight, or heterotrophs, which require an external source of food. It is not known whether protists were the progenitors of plants or animals.mushrooms🇧🇷 It is possible that several evolutionary lineages of protists evolved separately. Biologists consider protists to be a polyphyletic group, which means they probably don't have a common ancestor. The word protist comes from the Greek word for first, indicating that researchers believe that protists were the first eukaryotes on which they evolved.Terra.
Despite the great diversity of this kingdom, scientists have managed to divide protists into several groups. Protists can be classified into one of three main categories, animal-like, plant-like, and fungal-like. Grouping into one of three categories is based on an organism's mode of reproduction, diet, and motility. Animal-like protists are known asprotozoa, plant-like protists are algae and fungal-like protists areslime moldsand shapes of water.
Protozoa are all unicellular heterotrophs. They obtain their food by eating other organisms or dead organic matter. The word protozoan comes from the Latin word for first animals. Protozoa are divided into different phyla based on their mode of locomotion. They may use cilia, flagella or pseudopods. Some protozoa are sedentary, meaning they don't move. These organisms are parasites because they cannot actively consume food. They must live in an area of the host organism that is constantly supplied with food, such as an animal's intestines or bloodstream. Protozoa that use pseudopodia to move are known as amoebae, those that use flagella are called flagellates, those that use cilia are called ciliates, and those that do not move are called sporozoans.
Amoebas belong to the phylum Rhizopoda. These protists have no wall outside of them.cell membrane🇧🇷 This gives the cell flexibility and allows it to change shape. The word amoeba actually comes from the Greek word for change. Amoebas use extensions of theircell membrane, called pseudopods, for moving and devouring food. When the pseudopod picks up some food, the cell membrane closes around the food. This envelope forms a food vacuole. DigestiveDifficultthey are secreted into the food vacuole, which breaks down the food. The cell then absorbs the nutrients. Because amoebas live in water, dissolved nutrients from the environment can diffuse directly through their cell membranes. Most amoebas live in marine environments, although there are some freshwater species. Freshwater amoebae live in a hypotonic environment, so water constantly enters the cell by osmosis. To get around this problem, these amoebae use contractile vacuoles to pump excess water out of the cell. Most amoebas reproduce asexually by removing part of the cell membrane to form a new organism. Amoebas can form cysts when environmental conditions become unfavorable. These cysts can survive conditions such as water or nutrient deprivation. Two types of amoebas have shells, foraminifera and radiolarians.
The foramina have a hard shell.calcium carbonate🇧🇷 These shells are called tests. Foraminifera live in marine environments and are very common. When they die, their shells sink to the bottom, where they become part of the muddy ocean floor. Geologists use fossilized shells to determine the age of rocks and sediments. Shells on the seafloor gradually turn into limestone deposits that can be lifted up to form a land formation, such as the White Cliffs of Dover.England🇧🇷 Instead, radiolarians have silica shells.calcium carbonate🇧🇷 Both organisms have many tiny holes in their shells through which they extend their pseudopods. Pseudopods act like a sticky web that traps food scraps.
Flagellates have one or more flagella and belong to the phylum Zoomastigina. These organisms whip their flagella back and forth to move through the aquatic environment. These organisms are also known as zooflagellates. Flagellates are mostly unicellular and have a spherical or oblong shape. Some are also amoeboid. Many ingest their food through a primitive mouth called the oral sulcus. While most are motile, a class of flagellates called choanoflagellates are sessile. These organisms attach themselves to a rock or other substrate with a stalk.
Ciliates are members of the phylum Ciliopa. There are about 8,000 species of ciliates. These organisms move by the synchronized pulsing of the cilia that coat their bodies. They can be found almost anywhere, in marine or freshwater environments. The best-known ciliate is the organismparamecium🇧🇷 Paramecia have many well-developed organelles. Food enters the cell through the oral sulcus (lined with cilia to "sweep" food into the cell), where it travels to the esophagus, which packs the food into a food vacuole. Enzymes released into the food vacuole break down the food and the nutrients are absorbed into the cell. Waste is removed from the cell through an anal pore. Contractile vacuoles pump out excess water because paramecia live in a freshwater (hypotonic) environment. Paramecia have two nuclei, a macronucleus and a micronucleus. The larger macronucleus controls most of the cell's metabolic functions. The smaller micronucleus controls most of the pathways involved in sexual reproduction. Thousands of cilia emerge through the cuticle, a tough protective covering that surrounds the cell membrane. These cilia beat synchronously to move the paramecium in any direction. Below the cuticle are the trichocysts that shoot out small spines that help capture prey. Paramecia usually reproduce asexually when the cell divides into two new organisms after all organelles have duplicated. However, under unfavorable conditions, the organism can reproduce sexually. This form of sexual reproduction is calledconjugation🇧🇷 During conjugation, two paramecia come together in the oral cavity, where they exchange genetic material. They then separate and divide asexually, although this division does not necessarily occur immediately after exchanging genetic material.
Sporozoans belong to the phylumsporozoene🇧🇷 These organisms are sessile, so they cannot capture prey. Therefore, sporozoans are allparasites🇧🇷 As their name suggests, many of these organisms produce spores, reproductive cells that can give rise to a new organism. Sporozoans often have complex life cycles, as they often live on more than one host throughout their lives.
Plant or algae-like protists are all photosynthetic autotrophs. These organisms form the base of many food chains. Other creatures depend on these protists, either directly for food or indirectly for the oxygen they produce. Algae are responsible for more than half of the oxygen produced by photosynthetic organisms. Many forms of algae resemble plants, but differ in many ways. Algae do not have roots, stems or leaves. They don't have the waxy cuticle that plants have to prevent water loss. As a result, algae must live in areas where water is readily available. Algae do not have multicellular gametangia like plants. includeChlorophyll, but also contain other photosynthetic pigments. These pigments give algae distinctive colors and are used to classify algae into different phyla. Other features used to classify algae are storage of energy reserves and cell wall composition.
Members of the phylum Euglenophyta are known as euglenoids. These organisms are autotrophs and heterotrophs. There are hundreds of species of euglenoids. Euglenoids are protozoa and share characteristics of plants and animals. They are similar to plants in that they contain and are able to produce chlorophyll.photosynthesis🇧🇷 They don't have a cellulose cell wall like plants do; Instead, they have a protein membrane. Euglenoids are like animals in that they are mobile and respond to external stimuli. One specific species, Euglena, has a structure called an ocellus. This area of red pigment is sensitive to light. A Euglena may respond to its environment by moving to areas of bright light where photosynthesis takes place best. Under conditions where light is not available for photosynthesis, euglenoids can be heterotrophic and ingest their food. Euglenoids store their energy as paramylon, a type of polysaccharide.
Members of the phylum Bacillariophyta are calleddiatoms🇧🇷 Diatoms are single-celled organisms with shells made of silica. They are autotrophic and can live in marine or freshwater environments. They contain chlorophyll and pigments called carotenoids, which give them an orange-yellow color. Their bowls resemble small boxes with lids. These shells are covered with grooves and pores, giving them an ornate appearance. Diatoms can be radially or bilaterally symmetrical. Diatoms reproduce asexually in a unique way. The two shell halves are separated, each creating a new shell that fits into the original half. Therefore, each new generation produces offspring that are smaller than the parents. As each generation gets smaller and smaller, a lower limit is reached, about a quarter of the original size. At that point, the diatom produces gametes that fuse with gametes from other diatoms to produce zygotes. The zygotes develop into complete diatoms, which are ready to function.asexual reproductiononce again. When diatoms die, their shells sink to the ocean floor, forming deposits called diatoms.Terra🇧🇷 This residue can be collected and used as an abrasive or as an additive to lighten certain colors. Diatoms store their energy in the form of oils or carbohydrates.
WhatDinoflagellatesThey are members of the phylum Dinoflagellata. These organisms are unicellular autotrophs. Their cell walls contain cellulose, creating thick protective plaques. These plates contain two grooves at right angles to each other, each containing a flagellum. When the two flagella collide, they spin the organism around in the water. Most dinoflagellates are marine organisms, although some have been found in freshwater environments. Dinoflagellates contain chlorophyll as well as carotenoids and red pigments. They can be free-living or live in symbiotic relationships with jellyfish or corals. Some of the free-living dinoflagellates are bioluminescent. Many dinoflagellates produce potent toxins. One species in particular, Gonyaulax catanella, produces a deadly neurotoxin. These organisms sometimes multiply in large numbers in the summer, causing aRed Sea🇧🇷 During a red tide, there are so many of these organisms that the ocean appears red. Toxins released into the sea reach such high concentrations that many fish die. Dinoflagellates store their energy in the form of oils or polysaccharides.
The tensionrodofitaconsists notroot algae🇧🇷 The 4,000 species in this phylum are multicellular (with the exception of a few unicellular species) and live in marine environments. Red algae are typically found in tropical waters and sometimes along the coast in cooler areas. They live attached to the rocks by a structure called break point. Their cell walls contain thick polysaccharides. Some species also incorporate calcium carbonate from the ocean into their cell walls. Red algae contain chlorophyll and phycobilins, red and blue pigments that are involved in photosynthesis. The red pigment is called phycoerythrin and the blue pigment is called phycocyanin. Phycobilins absorb green, violet and blue light waves that can penetrate deep water. These pigments allowroot algaecarry out photosynthesis in deep water with low light. Reproduction in these organisms is a complex alternation between sexual and asexual phases. Red algae stores its energy as Florida starch.
The 1,500 species of brown algae belong to the phylum Phaeophyta. Most brown algae live in marine environments on rocks in cold water. They contain chlorophyll and a yellowish-brown carotenoid called fucoxanthin. The largest brown algae areSeetang🇧🇷 Kelp uses retaining clips to adhere to rocks. The body of an alga is called a thallus, which can grow up to 60 m in length. The stalk consists of three sections, the handle, the stem and the blade. Some species of brown algae have an air sac to keep the thallus floating on the surface of the water, where more light is available for photosynthesis. Brown algae store their energy as laminarin carbohydrate.
The tensionchlorophytais known as thealga verde🇧🇷 With over 7,000 species, this phylum is the most diverse of all algae. This onealga verdecontain chlorophyll as the main dye. Most live in freshwater, although there are some marine species. Their cell walls are made of cellulose, suggesting that green algae may be the ancestors of modern plants. Green algae can be unicellular, colonial or multicellular. An example of a single-celled green alga is Chlamydomonas. An example of colonial algae is Volvox. a volvoxCologneit is a hollow sphere made up of thousands of individual cells. Each cell has a single flagellum facing the outside of the sphere. Individual cells hit their flagella in a coordinated fashion, allowing the colony to move. Daughter colonies form inside the sphere, grow to a certain size, and are released when the mother colony breaks down. Spirogyra and Ulva are examples of multicellular green algae. Reproduction in green algae can be sexual and asexual. Green algae store their energy in the form of starch.
Mushroom-like protists resemble fungi during part of their life cycle. These organisms exhibit characteristics of fungi and protists. This group includes slime molds and aquatic fungi. They all obtain energy by breaking down organic materials and are therefore important for nutrient recycling. They can be brightly colored and live in cold, wet, and dark habitats. Slime fungi are classified as either plasmodial or cellular based on their modes of reproduction. Plasmodial slime molds belong to the phylum Myxomycota and cellular slime molds belong to the phylum Acrasiomycota.
Plasmodial slime fungi form a structure calledPlasmodio, a mass ofcytoplasmcontaining many nuclei but without cell walls or membranes to separate individual cells. Plasmodium is the slime's feeding stage.Schimmel🇧🇷 It moves like an amoeba, moving slowly through decaying organic material. It moves at a speed of 2.5 cm per hour and devoursmicroorganisms🇧🇷 The reproductive structure of plasmodial slime fungi occurs when the plasmodium forms a stem structure under unfavorable conditions. This structure produces spores that are released and can travel great distances. The spores land and produce a zygote that develops into a new plasmodium.
Cellular slime fungi exist as single cells during the feeding phase. These cells can also move around like an amoeba, devouring food in the process. Food cells reproduce asexually.cell division🇧🇷 When conditions become unfavorable, the cells clump together to form a large Plasmodium-like mass of cells. This mass of cells can move like an organism and looks a lot like a garden snail. The mass eventually develops into a stalked structure capable of sexual reproduction.
Water molds and downy mildew belong to the phylum Oomycota. They grow on the surface of dead organisms or plants, breaking down organic matter and absorbing nutrients. Most live in water or in humid areas. Water mold grows as a mass of fluffy white threads on dead material. The difference between these organisms and true fungi is that aquatic fungi produce flagellated reproductive cells throughout their life cycle.
Many protists can cause serious illness and disease.Malariait is caused, for example, by the protist Plasmodium. Plasmodia are sporozoans and are transmitted from person to person by female mosquitoes of the genus Anopheles. People with malaria have symptoms such as shivering, sweating, high fever and delirium. Africansleeping sickness, also known as African trypanosomiasis, is caused by another sporozoan, Trypanosoma. Trypanosoma is transmitted by AfricansTsetsefliege🇧🇷 This organism causes high fever and swollen lymph nodes. Eventually, the protist invades the victim's brain, where it causes a feeling of uncontrollable tiredness. Giardiasis is another example of a disease caused by a protist. This disease is caused byGarden, a sporozoan carried by muskrats and beavers. Giardiasis is characterized by fatigue, cramps, diarrhea and weight loss. amoebasRuhroccurs when a certain amoebaEntamoeba histolytica,infects thecolonfrom us. It is spread through infected food and water. This organism causes bleeding, diarrhea, vomiting, and sometimes death.
Members of the Protista kingdom can also be very beneficial to life on Earth. Many red algae species are popular edible foods in certain parts of the world. Red seaweed is rich in vitamins and minerals. Carrageenan, a polysaccharide obtained from red algae, is used as a thickening agentesand other foods. Giant kelp forests are rich ecosystems that provide food and shelter for many organisms. Trichonymphs are flagellates that live in the intestines of termites. These protozoa break down wood cellulose into carbohydrates that termites can digest.
Kingdom Protista is a diverse group of organisms. Some protists are harmful, but many more are beneficial. These organisms form the base of food chains, produce the oxygen we breathe, and play an important role in nutrient recycling. Many protists are also economically useful. As many of these unique organisms are discovered, people are sure to take advantage of the new uses and benefits that protists offer.
See too eukaryotes