A Survey of Eukaryotic Cells and Microorganisms

November 8, 2017 Medical

A Survey of Eukaryotic Cells and Microorganisms HISTORY OF EUKARYOTES: 1. Evidence indicates that the first Eukaryotic cells first appeared on the earth approximately 2 billion years ago. Fossilized cells appear in shale sediments from China, Russia and Australia the date from 850-950 million years ago. 2. Biologists have discovered evidence to suggest that the eukaryotic cell evolved from prokaryotic organisms by a process of intracellular symbiosis. 3. Some of the organelles that distinguish eukaryotic cells originated from prokaryotic cells that became trapped inside them. . The structure of these first eukaryotic cells was so versatile that eukaryotic microorganisms soon spread out into available habitats and adopted greatly diverse styles of living. 5. The first primitive eukaryotes were probably single celled and independent, but over time some forms began to cluster in permanent groupings called colonies. With further evolution some of these cells within colonies became specialized or adapted to perform a particular function advantageous to the whole colony such as locomotion, feeding, or reproduction. 6.

Multicellular organisms are composed of distinct groups of cells that cannot exist independently of the rest of the body. 7. The cell groupings of multicellular organisms that have a specific function are termed tissues and groups of tissues make up organs. 8. Protozoa , algae and fungi are unicellular 9. Plants, animals, mushrooms and seaweeds are multicellular. FORM AND FUNCTION OF THE EUKARYOTIC CELL: EXTERNAL AND INTERNAL STRUCTURES: A. Eukaryotic cells are complex and compartmentalized into individual organelles B. Major organelles and other structural features include: * Appendages (cilia and flagella) * Glycocalyx * Cell wall Cytoplasmic or cell membrane * Organelles (nucleus, nucleolus, endoplasmic reticulum, Golgi complex, mitochondria and chloroplasts) * Ribosomes * Cytoskeleton: microfilaments and microtubules THE KINGDOM OF FUNGI: -Common names of the macroscopic fungi are mushrooms, bracket fungi, and puffballs. Microscopic fungi are known as yeast and molds. A. Overall Morphology: At the cellular microscopic level, fungi are typical eukaryotic cells eigh thick cell walls. Yeasts are single cells that form buds and pseudohyphae ( a chain of easily separated spherical to sausage-shaped yeast cells partitioned by construction rather than by septa) .

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Hyphae are long tubular filaments that can be septate or nonseptate and grow in a network called a mycelium (the filamentous mass that makes up a mold. Composed of hyphae). Hyphae are characteristic of the filamentous fungi called molds. B. Nutritional Mode/ Distribution: All are heterotrophic (An organism that cannot synthesize its own food and is dependent on complex organic substances for nutrition). The majority are harmless saprobes (a microbe that decomposes organic remains from dead organisms), living of substrates (molecule upon which enzymes acts) such as dead animal or plant tissues.

A few are parasites (An organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host). Distribution is extremely widespread in many habitats. C. Reproduction: Primarily through spores formed on special reproductive hyphae. In asexual reproduction, spores are formed through budding, partitioning of a hypha or in special sporongenus structures, examples are conidia (asexual fungal spores shed as free units from the tips of fertile hyphae) and sporangiospores (a spore produced by a hollow single- or multicelled organ sporangium in fungi, ferns, and some other plants) .

In sexual reproduction spores are formed following fusion of male and female strains and the formation of a sexual structure. Sexual spores are one basis for classification. D. Major Groups: The four main phyla among the terrestrial fungi, given with sexual spore type are: Zygomycota; Ascomycota; Basidimycota and Chytridiomycota. E. Importance: Fungi are essential decomposersof plant and animal detritis in the environment. They are economically beneficial as sources of antibiotics; used in making foods and in genetic studies. Adverse impacts include: decomposition of fruits nd vegetables; human infectionsand some produce substances that are toxic if eaten. THE PROTISTS: –General group that traditionally includes single celled and colonial eukaryotic microbes that lack organizations into tissues A. THE ALGAE: * Overall Morphology: Are unicellular, colonial, filamentous, or larger forms such as seaweeds * Nutritional Mode/ Distribution: Photosynthetic; freshwater and marine water habitats, main component of plankton * Importance: Provide the basis of the food web in most aquatic habitats.

Certain algae produce neurotoxins that are harmful to humans and animals. B. THE PROTOZOA: –Include large single celled organism, a few are pathogens * Overall Morphology: Most are unicellular, lack a cell wall. The cytoplasm is divided into ectoplasm. Many convert to a resistant, dormant stage called a cyst (the resistant, dormant, but infectious form of protozoans). * Nutritional Mode/ Distribution: All are hetrotrophic (obtaining carbon for growth and energy from complex organic compounds).

Most are free living in a moist habitat like water or soil; feed by engulfing other microorganisms and organic matter. * Reproduction: Asexual by binary fission and mitosis; budding; sexual by fusion of free swimming gametes, and conjuction. * Major Groups: Protozoa are divided into four groups based upon mode of locomotion and type of reproduction. 1. Mastigophora—the flagellates that are motile by flagella 2. Sarcodina—the amoebas that ate motile by pseudopods 3. Ciliophora—the ciliates that are motile by cilia . Apicomplexa –the motility is not well developed and it produces unique reproductive structures. * Importance: Ecologically important in food webs and decomposing organic matter. Medical Significance: hundreds of millions of people are afflicted with one of the many protozoan infections such as malaria, amoebiasis, or trypanosomiasis. Diseases can be spread from host to host by insect vectors. C. THE PARASITIC HELMINTHS: –Includes three catagories: roundworms, tapeworms and flukes. Overall Morphology: Animals cells, multicellular, individual, organs specialized for reproduction, digestion, movement, protection though some of these reduced * Nutritional Mode/ Distribution: Includes embroyo, larval, and adult stages. Majority reproduce sexually. Sexes may be hermaphroditic (an organism, as an earthworm or plant, having normally both the male and female organs of generation. ) * Epidemiology: Developing countries in the tropics hardest hit with parasitic helminthes infictions; transmitted via ingestion of larvae or eggs in food; from soil or water. They afflict billions of humans.

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