This, obviously, is a form of asexual reproduction. But, remember that protists are an extremely diverse kingdom, and some protists can also reproduce sexually. Like all other eukaryotes, protists have a nucleus containing their DNA. They also have other membrane-bound organelles, such as mitochondria and the endoplasmic reticulum. Most protists are single-celled. Some are multicellular. Because the protist kingdom is so diverse, their ways of getting food and reproducing vary widely.
Most protists are aquatic organisms. They need a moist environment to survive. They are found mainly in damp soil, marshes, puddles, lakes, and the ocean. Some protists are free-living organisms. Others are involved in symbiotic relationships. They live in or on other organisms, including humans.
Most protists have motility. This is the ability to move. Protists have three types of appendages for movement. There may be one or more whip-like flagella. Cilia are similar to flagella, except they are shorter and there are more of them. Still other protists are composed of enormous, multinucleate, single cells that look like amorphous blobs of slime, or in other cases, similar to ferns.
Many protist cells are multinucleated; in some species, the nuclei are different sizes and have distinct roles in protist cell function. Single protist cells range in size from less than a micrometer to thousands of square meters giant kelp. Animal-like cell membranes or plant-like cell walls envelope protist cells. In other protists, glassy silica-based shells or pellicles of interlocking protein strips encase the cells.
The pellicle functions like a flexible coat of armor, preventing the protist from external damage without compromising its range of motion. Protists exhibit many forms of nutrition and may be aerobic or anaerobic. Protists that store energy by photosynthesis belong to a group of photoautotrophs and are characterized by the presence of chloroplasts.
Other protists are heterotrophic and consume organic materials such as other organisms to obtain nutrition. Amoebas and some other heterotrophic protist species ingest particles by a process called phagocytosis in which the cell membrane engulfs a food particle and brings it inward, pinching off an intracellular membranous sac, or vesicle, called a food vacuole.
The vesicle containing the ingested particle, the phagosome, then fuses with a lysosome containing hydrolytic enzymes to produce a phagolysosome, which breaks down the food particle into small molecules that diffuse into the cytoplasm for use in cellular metabolism.
Undigested remains ultimately exit the cell via exocytosis. Protist metabolism : The stages of phagocytosis include the engulfment of a food particle, the digestion of the particle using enzymes contained within a lysosome, and the expulsion of undigested materials from the cell. Subtypes of heterotrophs, called saprobes, absorb nutrients from dead organisms or their organic wastes. Some protists function as mixotrophs, obtaining nutrition by photoautotrophic or heterotrophic routes, depending on whether sunlight or organic nutrients are available.
The majority of protists are motile, but different types of protists have evolved varied modes of movement. Protists such as euglena have one or more flagella, which they rotate or whip to generate movement. Paramecia are covered in rows of tiny cilia that they beat to swim through liquids. Other protists, such at amoebae, form cytoplasmic extensions called pseudopodia anywhere on the cell, anchor the pseudopodia to a surface, and pull themselves forward.
Some protists can move toward or away from a stimulus; a movement referred to as taxis. Protists accomplish phototaxis, movement toward light, by coupling their locomotion strategy with a light-sensing organ. Different types of motility in protists : Protists use various methods for transportation. Protists live in a wide variety of habitats, including most bodies of water, as parasites in both plants and animals, and on dead organisms.
Protist life cycles range from simple to extremely elaborate. Certain parasitic protists have complicated life cycles and must infect different host species at different developmental stages to complete their life cycle. Some protists are unicellular in the haploid form and multicellular in the diploid form, which is a strategy also employed by animals.
The green algae are subdivided into the chlorophytes and the charophytes. The charophytes are the closest-living relatives of land plants, resembling them in morphology and reproductive strategies. Charophytes are common in wet habitats where their presence often signals a healthy ecosystem. The chlorophytes exhibit great diversity of form and function.
Chlorophytes primarily inhabit freshwater and damp soil; they are a common component of plankton. Chlamydomonas is a simple, unicellular chlorophyte with a pear-shaped morphology and two opposing, anterior flagella that guide this protist toward light sensed by its eyespot. More complex chlorophyte species exhibit haploid gametes and spores that resemble Chlamydomonas. The chlorophyte Volvox is one of only a few examples of a colonial organism, which behaves in some ways like a collection of individual cells, but in other ways like the specialized cells of a multicellular organism.
Volvox colonies contain to 60, cells, each with two flagella, contained within a hollow, spherical matrix composed of a gelatinous glycoprotein secretion. Individual Volvox cells move in a coordinated fashion and are interconnected by cytoplasmic bridges. Only a few of the cells reproduce to create daughter colonies, an example of basic cell specialization in this organism. Volvox aureus is a green alga in the supergroup Archaeplastida.
This species exists as a colony, consisting of cells immersed in a gel-like matrix and intertwined with each other via hair-like cytoplasmic extensions. True multicellular organisms, such as the sea lettuce, Ulva , are represented among the chlorophytes. In addition, some chlorophytes exist as large, multinucleate, single cells. Species in the genus Caulerpa exhibit flattened, fern-like foliage and can reach lengths of 3 meters. Caulerpa species undergo nuclear division, but their cells do not complete cytokinesis, remaining instead as massive and elaborate single cells.
Caulerpa taxifolia is a chlorophyte consisting of a single cell containing potentially thousands of nuclei. Amoebozoa are a type of protist that is characterized by the presence of pseudopodia which they use for locomotion and feeding. Protists are eukaryotic organisms that are classified as unicellular, colonial, or multicellular organisms that do not have specialized tissues.
This identifying property sets protists apart from other organisms within the Eukarya domain. The amoebozoans are classified as protists with pseudopodia which are used in locomotion and feeding. Amoebozoans live in marine environments, fresh water, or in soil.
In addition to the defining pseudopodia, they also lack a shell and do not have a fixed body. The pseudopodia which are characteristically exhibited include extensions which can be tube-like or flat lobes, rather than the hair-like pseudopodia of rhizarian amoeba.
Rhizarian amoeba are amoeboids with filose, reticulose, or microtubule-supported pseudopods and include the groups: Cercozoa, Foraminifera, and Radiolaria and are classified as bikonts. The Amoebozoa include several groups of unicellular amoeba-like organisms that are free-living or parasites that are classified as unikonts.
The best known and most well-studied member of this group is the slime mold. Additional members include the Archamoebae, Tubulinea, and Flabellinea. Pseudopodia structures : Amoebae with tubular and lobe-shaped pseudopodia, such as the ones seen under this microscope, would be morphologically classified as amoebozoans.
A subset of the amoebozoans, the slime molds, has several morphological similarities to fungi that are thought to be the result of convergent evolution. For instance, during times of stress, some slime molds develop into spore -generating fruiting bodies, similar to fungi. The slime molds are categorized on the basis of their life cycles into plasmodial or cellular types.
Plasmodial slime molds are composed of large, multinucleate cells that move along surfaces like an amorphous blob of slime during their feeding stage. Food particles are lifted and engulfed into the slime mold as it glides along. Upon maturation, the plasmodium takes on a net-like appearance with the ability to form fruiting bodies, or sporangia, during times of stress. Haploid spores are produced by meiosis within the sporangia. These spores can be disseminated through the air or water to potentially land in more favorable environments.
If this occurs, the spores germinate to form ameboid or flagellate haploid cells that can combine with each other and produce a diploid zygotic slime mold to complete the life cycle.
Badhamia utricularis : Badhamia utricularis: an example of a plasmodial slime mold with the ability to form a fruiting body. The cellular slime molds function as independent amoeboid cells when nutrients are abundant.
When food is depleted, cellular slime molds pile onto each other into a mass of cells that behaves as a single unit called a slug. Some cells in the slug contribute to a 2—3-millimeter stalk, drying up and dying in the process.
Cells atop the stalk form an asexual fruiting body that contains haploid spores. As with plasmodial slime molds, the spores are disseminated and can germinate if they land in a moist environment. One representative genus of the cellular slime molds is Dictyostelium, which commonly exists in the damp soil of forests.
Plasmodial slime mold: Physarum polycephalum : Physarum polycephalum is an example of a cellular slime mold. The Archamoebae are a group of Amoebozoa distinguished by the absence of mitochondria.
They include genera that are internal parasites or commensals of animals Entamoeba and Endolimax. A few species are human pathogens, causing diseases such as amoebic dysentery. The other genera of archamoebae live in freshwater habitats and are unusual among amoebae in possessing flagella. Most have a single nucleus and flagellum, but the giant amoeba, Pelomyxa , has many of each.
The Tubulinea are a major grouping of Amoebozoa, including most of the larger and more familiar amoebae like Amoeba , Arcella , and Difflugia. During locomotion, most Tubulinea have a roughly cylindrical form or produce numerous cylindrical pseudopods. Each cylinder advances by a single central stream of cytoplasm, granular in appearance, and has no subpseudopodia. This distinguishes them from other amoeboid groups, although in some members this is not the normal type of locomotion.
Privacy Policy. Skip to main content. Search for:. Groups of Protists. Excavata includes the protists: Diplomonads, Parabasalids and Euglenozoans. Diplomonads are defined by the presence of a nonfunctional, mitochrondrial-remnant organelle called a mitosome. Parabasalids are characterized by a semi-functional mitochondria referred to as a hydrogenosome; they are comprised of parasitic protists, such as Trichomonas vaginalis.
Euglenozoans can be classified as mixotrophs, heterotrophs, autotrophs, and parasites; they are defined by their use of flagella for movement.
Key Terms mitosome : an organelle found within certain unicellular eukaryotes which lack mitochondria hydrogenosome : a membrane-bound organelle found in ciliates, trichomonads, and fungi which produces molecular hydrogen and ATP kinetoplast : a disk-shaped mass of circular DNA inside a large mitochondrion, found specifically in protozoa of the class Kinetoplastea.
Giardia lamblia The mammalian intestinal parasite Giardia lamblia, visualized here using scanning electron microscopy, is a waterborne protist that causes severe diarrhea when ingested. Chromalveolata: Alveolates Alveolates are defined by the presence of an alveolus beneath the cell membrane and include dinoflagellates, apicomplexans and ciliates.
Learning Objectives Evaluate traits associated with protists classified as alveolates which include dinoflagellates, apicomplexans, and ciliates. Key Takeaways Key Points Alveolates are classified under the group Chromalveolata which developed as a result of a secondary endosymbiotic event. Dinoflagellates are defined by their flagella structure which lays perpendicular and fits into the cellulose plates of the dinoflagellate, promoting a spinning motion.
Apicomplexans are defined by the asymmetrical distribution of their microtubules, fibrin, and vacuoles; they include the parasitic protist Plasmodium which causes malaria. Ciliates are defined by the presence of cilia such as the oral groove in the Paramecium , which beat synchronously to aid the organism in locomotion and obtaining nutrients.
Ciliates are defined by the presence of cilia, which beat synchronously, to aid the organism in locomotion and obtaining nutrients, such as the oral groove in the Paramecium. Key Terms osmoregulation : the homeostatic regulation of osmotic pressure in the body in order to maintain a constant water content plastid : any of various organelles found in the cells of plants and algae, often concerned with photosynthesis conjugation : the temporary fusion of organisms, especially as part of sexual reproduction.
Chromalveolata: Stramenopiles Stramenophiles include photosynthetic marine algae and heterotrophic protists such as diatoms, brown and golden algae, and oomycetes. Learning Objectives Describe characteristics of the following Stramenophiles: diatoms, brown algae, golden algae, and oomycetes.
Diatoms, present in both freshwater and marine plankton, are unicellular photosynthetic protists that are characterized by the presence of a cell wall composed of silicon dioxide that displays intricate patterns.
Golden algae, present in both freshwater and marine plankton communities, are unicellular photosynthetic protists characterized by the presence of carotenoids yellow-orange photosynthetic pigments.
Oomycetes, commonly referred to as water molds, are characterized by their fungus-like morphology, a cellulose-based cell wall, and a filamentous network used for nutrient uptake.
Oomycetes, commonly referred to as water molds, are characterized by their fungus-like morphology, a cellulose-based cell wall and a filamentous network used for nutrient uptake. Key Terms stipe : the stem of a kelp raphe : a ridge or seam on an organ, bodily tissue, or other structure, especially at the join between two halves or sections saprobe : an organism that lives off of dead or decaying organic material. Oomycete : A saprobic oomycete engulfs a dead insect.
Rhizaria Rhizaria are a supergroup of protists, typically amoebas, that are characterized by the presence of needle-like pseudopodia. Learning Objectives Describe characteristics associated with Rhizaria. Key Takeaways Key Points The needle-like pseudopodia are used to carry out a process called cytoplasmic streaming which is a means of locomotion or distributing nutrients and oxygen.
Two major subclassifications of Rhizaria include Forams and Radiolarians. Forams are characterized as unicellular heterotrophic protists that have porous shells, referred to as tests, which can contain photosynthetic algae that the foram can use as a nutrient source.
Radiolarians are characterized by a glassy silica exterior that displays either bilateral or radial symmetry. Key Terms pseudopodia : temporary projections of eukaryotic cells test : the external calciferous shell of a foram.
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