Biology 2483A Lecture Notes - Lecture 10: Gastrointestinal Tract, Parasitoid, Whitefly

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11 Dec 2017

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Symbionts: organisms that live in or on other organisms: more than half of earth"s species are symbionts, our own bodies can be a home to many other species. Examples: athlete"s foot fu(cid:374)gus, fleas, (cid:373)ites, li(cid:272)e, a(cid:374)d ti(cid:272)ks. Some of these parasites also transmit disease organisms. Many disease organisms are endoparasites: the alimentary canal is excellent habitat for many parasites. Most do not eat host tissue, but rob the host of nutrients: tape(cid:449)or(cid:373)s atta(cid:272)h to the host"s i(cid:374)testi(cid:374)al (cid:449)all a(cid:374)d a(cid:271)sor(cid:271) digested food. Many endoparasites live in the host"s tissues/cells: examples: Yersinia pestis, the bacterium that causes the plague: mycobacterium tuberculosis, the bacterium that causes tuberculosis. Some hosts can encapsulate endoparasites, or their eggs, to make them harmless. In studies of wild flax and a rust pathogen: In flax populations with few resistance genes, there is no advantage to being virulent.

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Fungi Fungi are the great decomposers of the biosphere. Most plants form mycorrhizae with fungi to increase absorptive area without having to grow more roots, in this relationship fungi recieve carbohydrates from plants. Humans consume fungi, mushrooms, may use fungi as a source of drugs for blood pressure, antibiotics and immunosuppresive drugs. Fungi are used in biotechnology to produce fermetation products, and some have been very useful models to study gentics in eukaryotic cells that are unicellular such as yeasts. About one third of fungi may cause infections, mycoses, in plants, animals and humans. Fungi tolerate concentration of salt and sugar that plasmolyze bacteria in perserved foods exposed to air which contains fungal spores may germinate and may spoil food. Fungi have two body shapes, molds and yeasts. Mold are large and made of long filamentous hyphae. Hyphae form mats called mycelium ( plural is mycelia). Mycelia may extend for miles underground, making fungi the largest organism on earth. The visible portion of subterrean fungi are the fruitng bodies such as mushrooms. Yeasts are globular and unicellular. They may bud forming up 24 daughter cells from a single cell. When budding is incomplete it may produce a psuedohypa. Fungi that may exist in both body types are dimorphic fungi. In general, the yeast form of a dimorphic fungus is a pathogen, the filamentous form is not pathogenic. Examples are Histoplasmosis capsulatum (histoplasmosis) and Coccidiodes immitis (coccidioidomycosis). Fungi are saprobes, they absorb nutrients from the remains of dead plants or they lasso nematodes. Fungi may derive nutrients from a living plant utilizing haustoria which are modified hyphae that penetrate living plant tissue. Some fungi use melanin to absorb gamma rays which they convert to chemical energy. Some herbivores have fungi in thier gut microbiome to help digest plants. Zygomycota contains 1100 species and reproduces asexually through sporangiaspores, which form in a sac called a sporangium on a stalk called a sporangiaphore. An example is Nosema which is an obligate intracellular parasite in insects and honeybees. Ascomycota havd 32,000 species form haploid ascospores in sacs called ascus (asci plura) and reproduce asexually with condiospores which develop on the tips of hyphae on stalks called conidiophores. Examples are Claviceps purpurea, ergot, which grows on grain and causes abortions in cattle and hallucinations in humans. Penicillium the source of the first antibiotic discovered by Fleming in the 1940s. Saccharomyces, a facultative anaerobe, ferments sugar to produce alcohol and carbon dioxide gas and is used in baking and brewing. Neurospora was used as a model to study molecular biology, Beadle and Tatum established one gene one enzyme using this model organism.

14. Why are there more antibacterial drugs than antifungal drugs? Basidiomycota have fruiting bodies called basidiocarps. Basidiospores are dispersed by the wind and germinate in warm moist environments. An example is the pathogen Cryptococcus neoformans the leading cause of fungal meningitis

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Biology 2483A Lecture Notes - Lecture 10: Gastrointestinal Tract, Parasitoid, Whitefly

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