In addition they have tails, or flagella, they use to maneuver the colony. Freshwater protists like a paramecium are osmoregulators. They expel extra water by the use of a contractile vacuole. Read More: How do you beat chain Chomplets in unchained?
Do they weigh you before parasailing? Can you unlock Mario Kart Wii levels in multiplayer? Are forsythia bushes poisonous to dogs? How do you go down a line without pressing Enter? How do you find the range rule of thumb? They need a moist environment to survive and are found in places where there is enough water for them, such as marshes, puddles, damp soil, lakes, and the ocean.
Some protists are free-living organisms and others are symbionts, living inside or on other organisms, including humans.
Plant-like protists are autotrophs. This means that they produce their own food. They perform photosynthesis to produce sugar by using carbon dioxide and water, and the energy from sunlight, just like plants. Protists can be unicellular single-celled or multicellular many-celled. Bacteria and archaea are prokaryotes, while all other living organisms — protists, plants, animals and fungi — are eukaryotes. The green, slimy patches that grows in moist areas or stagnant water is called algae.
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Pseudopodia function to trap and engulf food particles and to direct movement in rhizarian protists. These pseudopods project outward from anywhere on the cell surface and can anchor to a substrate. The protist then transports its cytoplasm into the pseudopod, thereby moving the entire cell.
This type of motion, called cytoplasmic streaming , is used by several diverse groups of protists as a means of locomotion or as a method to distribute nutrients and oxygen.
Foraminiferans, or forams, are unicellular heterotrophic protists, ranging from approximately 20 micrometers to several centimeters in length, and occasionally resembling tiny snails [link]. As a group, the forams exhibit porous shells, called tests that are built from various organic materials and typically hardened with calcium carbonate.
The tests may house photosynthetic algae, which the forams can harvest for nutrition. Foram pseudopodia extend through the pores and allow the forams to move, feed, and gather additional building materials. Typically, forams are associated with sand or other particles in marine or freshwater habitats.
Foraminiferans are also useful as indicators of pollution and changes in global weather patterns. A second subtype of Rhizaria, the radiolarians, exhibit intricate exteriors of glassy silica with radial or bilateral symmetry [link].
Needle-like pseudopods supported by microtubules radiate outward from the cell bodies of these protists and function to catch food particles. The shells of dead radiolarians sink to the ocean floor, where they may accumulate in meter-thick depths. Preserved, sedimented radiolarians are very common in the fossil record. Red algae and green algae are included in the supergroup Archaeplastida. It was from a common ancestor of these protists that the land plants evolved, since their closest relatives are found in this group.
Molecular evidence supports that all Archaeplastida are descendents of an endosymbiotic relationship between a heterotrophic protist and a cyanobacterium.
The red and green algae include unicellular, multicellular, and colonial forms. Red algae, or rhodophytes, are primarily multicellular, lack flagella, and range in size from microscopic, unicellular protists to large, multicellular forms grouped into the informal seaweed category. The red algae life cycle is an alternation of generations. Some species of red algae contain phycoerythrins, photosynthetic accessory pigments that are red in color and outcompete the green tint of chlorophyll, making these species appear as varying shades of red.
Other protists classified as red algae lack phycoerythrins and are parasites. Red algae are common in tropical waters where they have been detected at depths of meters. Other red algae exist in terrestrial or freshwater environments. The most abundant group of algae is the green algae. The green algae exhibit similar features to the land plants, particularly in terms of chloroplast structure. That this group of protists shared a relatively recent common ancestor with land plants is well supported.
The green algae are subdivided into the chlorophytes and the charophytes. The charophytes are the closest living relatives to land plants and resemble them in morphology and reproductive strategies. Charophytes are common in wet habitats, and their presence often signals a healthy ecosystem. The chlorophytes exhibit great diversity of form and function.
Chlorophytes primarily inhabit freshwater and damp soil, and 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 [link]. 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. 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 [link]. Caulerpa species undergo nuclear division, but their cells do not complete cytokinesis, remaining instead as massive and elaborate single cells.
The amoebozoans characteristically exhibit pseudopodia that extend like tubes or flat lobes, rather than the hair-like pseudopodia of rhizarian amoeba [link].
The Amoebozoa include several groups of unicellular amoeba-like organisms that are free-living or parasites. 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, much like 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 and move along surfaces like an amorphous blob of slime during their feeding stage [link]. 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, and 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. The cellular slime molds function as independent amoeboid cells when nutrients are abundant [link].
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. View this video to see the formation of a fruiting body by a cellular slime mold.
The opisthokonts include the animal-like choanoflagellates, which are believed to resemble the common ancestor of sponges and, in fact, all animals. Choanoflagellates include unicellular and colonial forms, and number about described species.
These organisms exhibit a single, apical flagellum that is surrounded by a contractile collar composed of microvilli. The collar uses a similar mechanism to sponges to filter out bacteria for ingestion by the protist.
The morphology of choanoflagellates was recognized early on as resembling the collar cells of sponges, and suggesting a possible relationship to animals. The Mesomycetozoa form a small group of parasites, primarily of fish, and at least one form that can parasitize humans.
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