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   1. a. Characteristics The characteristics of phylum sarcomastigophora are : (1) Nucleus is of one type except in the stages of certain foraminifera. (2) Locomotory organ either pseudopodia or flagella or both. (3) Reproduction asexual , but when sexually it is essentially by syngamy (4) Spore formation is absent. Example : Amoeba, Euglena etc. b. Ciliates have several distinguishing features and they are one of the most clearly defined groups of protist. These features are: Cilia at some stage during the life cycle. Cilia are fine hair-like organelles that beat rhythmically for locomotion or to create feeding currents. Body or somatic cilia lie in rows called kineties (sing. kinety). Oral cilia aid in food capture and may be simple or form complex compound stuctures. The cilia are anchored within the cell with three unique fibers, called the Infraciliature. The Infraciliature consists of a ribbon transverse microtubules, a ribbon of postciliary microtubules, and a striated fibrillar kinetodemal fiber. There are two types of nuclei: a macronucleus and a micronucleus. The macronucleus is vegetative and is responsible for protein transcription (in other words the day-today operations of the cell). The micronucleus is smaller and primarily functions in exchange of genetic material during conjugation. The fission line of cell division cuts at right angles to the kineties, dividing the mother cell into an anterior proter and a posterior opisthe. During cell division, the oral structure of the opiste must be formed and it does so in a process called stomatogenesis. Stomatogenesis varies somewhat from group to group in the ciliates. Genetic recombination is by conjugation. Most organisms have gametic genetic recombination. Ciliates have a unique process called conjugation in which micronuclei are exchanged. Food is ingested through a permanent opening called a cytostome where it is enclosed in a food vacuole. c. Dinoflagellates Dinoflagellates are microorganisms that are regarded as algae. Their wide array of exotic shapes and, sometimes, armored appearance is distinct from other algae. The closest microorganism in appearance are the diatoms .  Dinoflagellates are single-celled organisms. There are nearly 2000 known living species. Some are bacterial in size, while the largest, Noctiluca, can be up to two millimeters in size. This is large enough to be seen by the unaided eye. Ninety per cent of all known dinoflagellates live in the ocean, although freshwater species also exist. In fact, dinoflagellates have even been isolated from snow. In these environments, the organisms can exist as free-living and independent forms, or can take up residence in another organism. A number of photosynthetic dinoflagellates inhabit sponges, corals, jellyfish, and flatworms. The association is symbiotic. The host provides a protective environment and the growth of the dinoflagellates impart nutritive carbohydrates to the host. As their name implies, flagella are present. Indeed, the term dinoflagellate means whirling flagella. Typically, there are two flagella. One of these circles around the body of the cell, often lying in a groove called the cingulum. The other flagellum sticks outward from the surface of the cell. Both flagella are inserted into the dinoflagellate at the same point. The arrangement of the flagella can cause the organism to move in a spiral trajectory. The complex appearance, relative to other algae and bacteria , is carried onward to other aspects of dinoflagellate behavior and growth. Some dinoflagellates feed on other microorganisms, while others produce energy using photosynthesis. Still other dinoflagellates can do both. The life cycle of the organisms is also complex, involving forms that are immobile and capable of movement and forms that are capable of sexual or asexual reproduction (bacteria, for example, reproduce asexually, by the self-replication of their genetic material and other constituents). Dinoflagellates are primarily asexual in reproduction. Some dinoflagellates contain plates of cellulose that lie between the two surface membranes that cover the organism. These plates function as protective armor. Dinoflagellates are noteworthy for several reasons. They are one of the bedrocks of the food chain, particularly in the oceans and lakes of the world. Their numbers can be so great that they are evident as a mass of color on the surface of the water. Sometimes satellite cameras can even visualize these blooms. This abundant growth can consume so much oxygen that survival of other species in the area is threatened. As well, some dinoflagellates can produce toxins that can find their way into higher species, particularly those such as shellfish that feed by filtering water through them. Paralytic shellfish poisoning, which harms the neurological system of humans, is an example of a malady associated with the consumption of clams, mussels, and oysters that are contaminated with dinoflagellate toxins known as saxitoxin and brevitoxin. Saxitoxin is extremely potent, exerting its effect on the neurological system at concentrations 10,000 times lower than that required by cocaine. Another example of a dinoflagellaterelated malady is a disease called ciguatera, which results from eating toxin-contaminated fish. A third distinctive feature of dinoflagellates concerns their nucleus . The deoxyribonucleic acid shares some features with the DNA of eukaryotes , such as the presence of repeated stretches of DNA. But, other eukaryotic features, such as the supportive structures known as histones, have as yet not been detected. Also, the amount of DNA in dinoflagellates is far greater than in eukaryotes. The nucleus can occupy half the volume of the cell.  As with other microorganisms, dinoflagellates have been present on the Earth for a long time. Fossils of Arpylorus antiquus have been found in rock that dates back 400 million years. And, fossils that may be dinoflagellate cysts have been found in rock that is almost two billion years old. Current thought is that dinoflagellates arose when a bacterium was swallowed but not digested by another microorganism. The bacteria became symbiotic with the organism that swallowed them. This explanation is also how mitochondria are thought to have arisen. Dinoflagellates cysts are analogous to the cysts formed by other microorganisms. They function to protect the genetic material during periods when conditions are too harsh for growth. When conditions become more favorable, resuscitation of the cyst and growth of the dinoflagellate resumes. Dinoflagellates are sometimes referred to as Pyrrhophyta, which means fire plants. This is because of their ability to produce biological luminescence, akin to that of the firefly. Often, these luminescent dinoflagellates can be seen in the wake of ocean-going ships at night. d. Apicomplexa is a phylum made up almost entirely of parasites. Apicomplexans are distinguished by their unique method of entering host cells. Apicomplexan parasites cause a number of serious illnesses, such as babesiosis in dogs and cattle, leucocytozoonosis in birds, and most significantly malaria in humans. They are grouped with dinoflagellates and ciliates to make up the Alveolata, a higher order whose most common shared characteristic is the cortical alveolae, flattened vesicle-like structures which are found just under the plasma membrane. Unlike their Alveolate relations, however, Apicomplexans have undergone degenerative evolution, losing all flagella and cilia. Their unique characteristic, the product of past endosymbiosis, is the apical complex, a group of secretory organelles, in particular the apicoplast, which enable the parasitic cells to invade the host cell. 2. a. d. The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of plastid called an apicoplast, and an apical complex structure. The organelle is an adaptation that the apicomplexan applies in penetration of a host cell. The Apicomplexa are unicellular and spore-forming. All species are obligate endoparasites of animals,[3] except Nephromyces, a symbiont in marine animals, srcinally classified as a chytrid fungus.[4] Motile structures such as flagella or pseudopods are present only in certain gamete stages. The Apicomplexa are a diverse group that includes organisms such as the coccidia, gregarines, piroplasms, haemogregarines, and plasmodia. Subgroups Within this phylum are three groups — coccidians, gregarines, and haemosporidians. The coccidians and gregarines appear to be relatively closely related.  Perkinsus , while once considered a member of the Apicomplexa, has been moved to a new phylum — Perkinsozoa.[12] Gregarines Trophozoite of a gregarine Main article: Gregarinasina The gregarines are generally parasites of annelids, arthropods, and mollusks. They are often found in the guts of their hosts, but may invade the other tissues. In the typical gregarine lifecycle, a trophozoite develops within a host cell into a schizont. This then divides into a number of merozoites by schizogony. The merozoites are released by lysing the host cell, which in turn invade other cells. At some point in the apicomplexan lifecycle, gametocytes are formed. These are released by lysis of the host cells, which group together. Each gametocyte forms multiple gametes. The gametes fuse with another to form oocysts. The oocysts leave the host to be taken up by a new host. Coccidians Dividing Toxoplasma gondii (Coccidia) parasites Main article: Coccidia In general, coccidians are parasites of vertebrates. Like gregarines, they are commonly parasites of the epithelial cells of the gut, but may infect other tissues. The coccidian lifecycle involves merogony, gametogony, and sporogony. While similar to that of the gregarines it differs in zygote formation. Some trophozoites enlarge and become macrogamete, whereas others divide repeatedly to form microgametes (anisogamy). The microgametes are motile and must reach the macrogamete to fertilize it. The fertilized macrogamete forms a zygote that in its turn forms an oocyst that is normally released from the body. Syzygy, when it occurs, involves markedly anisogamous gametes. The lifecycle is typically haploid, with the only diploid stage occurring in the zygote, which is normally short-lived. The main difference between the coccidians and the gregarines is in the gamonts. In the coccidia, these are small, intracellular, and without epimerites or mucrons. In the gregarines, these are large, extracellular, and possess epimerites or mucrons. A second difference between the coccidia and the gregarines also lies in the gamonts. In the coccidians, a single gamont becomes a macrogametocyte, whereas in the gregarines, the gamonts give rise to multiple gametocytes.

Chap 4

Oct 7, 2019

multiplself

Oct 7, 2019
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