Ph 162A Lec 2 Protozoans

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What are protozoans?

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unicellular eukaryotic marine bottom dwellers

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Are protozoans heterotrophs or autotrophs?

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They are heterotrophic and use organic carbon for growth by consuming other organisms.

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What are the structures related to feeding?

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Many merely absorb the nutrients they need directly through the membrane. Some use pseudopodia, when the plasma membrane engulfs a food. Some have a cytostome, a mouth-like structure surrounded by cilia to create a current to pull food in.

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How do they digest food?

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in a food vacuole with digestive enzymes that break down

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How are unwanted by-products excreted?

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involves diffusion and a contractile vacuole

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four forms of locomotion protozoans use

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1. pseudopodia
2. flagella
3. cilia
4. adhesive disc

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pseudopodia

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extension of a pseudopodium by an amoeba is accompanied by the constant flow of cytoplasm in direction of the extension

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flagella

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protozoans usually have between 2 or 3. each flagellum has 9+2 structure: 9 pairs of microtubules and 1 pair of 2 in the middle. long whiplike structure, propel by beating

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undulating membrane

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modified flagellum found in certain protozoans

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cilia

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much shorter and in larger #s than flagella. when fused together called cirri.

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adhesive disc

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helps resist movement; like a sucker. eg. Giardia

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structures related to protection

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1. pellicle
2. cysts
3. trophozoite

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pellicle

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like a cell wall; thick covering external to membrane

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shells of mineral substances

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cysts and trophozoite: composed of calcite and organic material, sediment particles, or mineral secretions

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cysts

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also trichocyst; when food is low, intracellular organelles shoot outward and release poisons eg. when Entamoeba histolytica forms cysts it causes amoebiasis

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protozoa asexual reproduction

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1.) binary fission- equal halves: eg. T. vaginalis
2.) schizogony- simultaneous multiple fission eg. in sporozoans

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protozoa sexual reproduction

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1.) syngamy- union of 2 unlike haploid cells eg. in sporozoans
2.) conjugation- 2 cells of unlike mating types exchange micronuclei eg. in ciliates

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how are protozoans classified?

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they are classified into 4 groups primarily by locomotion, cellular organization, method of obtaining nutrients, methods of protection, methods of reproduction, and biochemical analyses of nucleic acids

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what are some interactions between protozoans and humans?

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most species of protozoans are free-living in soil and water, and do not relate directly to the health and disease of humans. some contribute to health: eg. those that prevent tooth decay and gum disease

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backpacker's diarrhea

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caused by Giardia in water; because of poor hygeine, can be diagnosed using immunofluorescence assay (DFA), Ab's tagged with fluorescent markers are added to stool and incubated. visualization is under a fluorescent microscope. giardia cysts are green flowing ovoid objects

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helminthes

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worms; certain phases of life are microscopic (eg. ova) and have complex and characteristic individual life cycles; some are simple (1 host, 2 forms), or complex (several hosts, 4 forms)

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different life forms

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all worms have at least 2 forms; the ovum (fertilized, and containing the embryo) and the adult. some worms also have 1 or 2 larval stages between the ovum and the adult. for parasitic helminths each phase may involve a diff species of animal for a host

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definitive host

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can harbor an adult parasite; can reproduce

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intermediate host

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harbor larval stages; no sexual reproduction occurs in that host

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helminth cell and feeding

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they are multicellular and heterotrophs. some absorb directly through skin, some have well developed mouth for ingestion. some have advanced excretory systems. parasitic types have special structures for attachment to host membranes

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helminth sensory system

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aid in survival; have ganglia and nerve trunk. tactile and chemosense chemical receptors, no brains
eg. liver fluke- 3rd most prevalent parasite worm in the world; endemic to japan, china, taiwan, and SE asia

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Trypanosoma cruzi

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causes trypanosomiasis disease (chagas) in humans and animals in America. Reduviid bug deposits feces on the skin surface and subsequently bites. The human host scratches the bite area which facilitates penetration of the infected feces. Has undulating membrane, uses an insect vector

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locomotion in helminths

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muscle cells in adult form and cilia in larval forms

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protection in helminths

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adult forms have a thick skin to resist digestion by stomach enzymes and ova of helminths have thick shells for protection in and out of host

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helminth reproduction

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primarily sexual, but may occasionally be asexual. dioecious and hermaphroditic

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dioecious

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mating between separate indiv male and females --> feritilized eggs

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hermaphroditic

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both male and female reproductive organs in one individual. ova can be fertilized by sperm from another nearby or by itself.

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parthogenesis

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unfertilized female can develop new complete individual without fertilization.

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arthropods

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from the phylum arthropoda. very advanced animals with well developed systems. sexual reproduction

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chitin

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hard material which constitutes exoskeleton for protection

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2 classes of arthropods related to microbio

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insecta, arachnids

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importance of arthropods to public health

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ticks and mites as vectors of disease-causing viruses, bacteria, and protozoans; parasites (ectoparasites) because live on exterior of human body: ticks, dust mite, lice; release poisons or allergens eg. dust mites4