Chapter 17 Protists

17.1 Protists are the most diverse of all eukaryotes protists: eukaryotes that are not animals, plants, or fungi –Most are unicellular and free-living –Some are colonial –Some are multicellular, like seaweed

Structure Internal membranes, nucleus with a nuclear envelope, organelles like chloroplasts(in some) and mitochondria Protists are so different from each other that eventually the classification system will divide them into several kingdoms

Cells More complex than humans Human cells are highly specialized Protists cells must carry out all life functions

Types of Nutrition Autotroph vs heterotroph Animal-like: protozoans –Heterotroph Fungus-like –Heterotroph; feed on decaying matter Plant-like: algae –Autotroph; make food by photosynthesis

17.2 Protozoans ingest their food Protozoans; animal-like Eat bacteria, other protists, non-living organic matter Lack cell wall Live in most aquatic environments & some in body fluids Classified by movement

Flagellates zooflagellates: move by one or more flagella (whip-like) Reproduce asexually by binary fission Most are free-living; exceptions are parasites (ex Giardia, Trypanosoma, Trichonympha)

Parasites Giardia: infects human intestine and can cause abdominal cramps and diarrhea –Infected by drinking water contaminated with animal feces –2 separate nuclei, no mitochondria (the hypothesis is that they lost in in evolution) –No cellular respiration--> fermentation (which is why it can live in intestines; no need for oxygen)

Trypanosoma –Causes African sleeping sickness –Spread by tsetse fly Trichonympha –Symbiotic in gut of termites –Digest cellulose

Sarcodina pseudopodia: extensions of cytoplasm and plasma membrane –Amoeba- moves and feeds by pseudopodia

forams: marine protozoans with porous shells made of organix material and calcium carbonate –Extends pseudopodia through pores Forms limestone by build up of shells in sediment

Ciliates ciliates: diverse group of protists named for the hair-like projections called cilia to move and feed Cilia are shorter and more numerous than flagella and are arranged in rows or clusters Paramecium - free-living pond water organism

Stylonchia - leg-like structures, many cilia together Stentor - attaches to a surface and uses cilia around its “mouth” to capture food like a whirlpool

Bursaria & Didinium

Two kinds of nuclei –Macronucleus: coordinates various cellular activity –1 to 80 micronuclei: sexual reproduction Reproduces by binary fission or conjugation Structure and Reproduction

Sporozoa apicomplexans: parasites with no active motility –“apical complex” - organelles at tip of cell specialized for penetrating host cell Plasmodium - organism that causes malaria –Reproduces asexually in humans, sexually in mosquitos

17.3 Fungus-like protists Plasmodial Slime Molds: protist that feeds on decaying matter –Not multicellular plasmodium: single mass of cytoplasm undivided by membranes or cell walls containing many nuclei –“supercell” - behaves like an amoeba –Large surface area for increased availability of food, water, and oxygen –Cytoplasm streams in pulsing flows to distribute nutrients

Plasmodial Slime Mold Reproduction sporangia: fruiting bodies that function as reproductive structures –Only grow during lack of food and water –Produce spores that dispearse in the wind –Good conditions= spore releases active haploid cell which fuses with another to form a zygote

Cellular Slime Molds cellular slime molds: decomposers that live mainly on decaying matter Both uni- and multicellular stages

Dictyostelium 3 life cycle stages: individual, colony, spore 1.Individual - amoeba-like Spends most time here during food periods Separate and reproduce asexually 2.Colony - multicellular - food is scarce Secrete chemicals that attract each other Form stalk or spores 3.Spores- good conditions Amoeba-like cells emerge from spores Asexual

Water Molds Freshwater habitats; some parasitic on fish gills and skin –Unicellular or –Thin, branching filaments with many nuclei Reproduce sexually –Release motile spores with 2 flagella

Downy Mildews Produce egg cell; flagellated spores Phytophthora infestans - plant parasite –Infected potato crops in Ireland –Potatoes are asexual so no resistance through variation Related more closely to algae than slime molds

17.4 Algae are photosynthetic protists Classified by cell wall, photopigments, structure, carb storage, nucleic acid sequence euglenoids: group of single-celled, photosynthetic protists that have 1 or 2 flagella and no cell walls

Euglena Live in fresh water Plasma membrane is tough and has chloroplasts Flagellum at base near eyespot Swims toward light for photosynthesis In the dark, absorbs nutrients instead of making food

Dinoflagellates dinoflagellates: unicellular, mostly photosyn., cell walls of cellulose, 2 flagella –Both fresh and salt plankton: communities of organisms that drift near the surface phytoplankton: photosyn organism in plankton zooplankton: plankton that are protozoans

Red Tide Large number of dinoflagellates that turn coastal marine waters pinkish-orange –Produce toxins that kill fish –Can be deadly to humans that eat the shellfish

Bioluminescence Ability to produce light

Diatoms Unicellular with glass-like cell wall –Contains silica; same mineral that makes up glass –Variety of shapes Contain chlorophyll and other pigments Store food as oil; float to surface for photosynthesis When they die, glass walls accumulate and fossilize –Sediments called diatomaceous earth –Used as filter material, grinding and polishing, toothpaste

Seaweeds Large, multicellular marine algae Like plants but no true roots, stems, leaves 3 types: brown, red, green Unusual polysaccharide human’s can’t digest Gives slimy feel; helps cushion organisms Carrageenan - thicken foods (pudding) Algin - thicken foods, cosmetics, paints Agar - gelatin-like for cultures

Brown Algae Grow on rocky shores; tolerate wave action Kelp - grown to 60m “holdfasts” - root-like structures to help anchor

Red Algae Warm coastal waters Can live in deep water; red can absorb blue & green light (which goes deepest in water) Most are multicellular Coralline algae - hard cell walls from mineral deposits; coral reefs Depend on currents to bring gametes together

Green Algae Most live in fresh water Uni-, multicell., and colonial Phytoplankton - unicellular Chlamydomonas - uni-, fresh water –2 flagella, toward light Volvox - colonial –Hollow ball Ulva - multi- –Seaweeds –Ancestors of plants

17.5 Plants, fungi, and animals evolved from protists Scientists believe that plants, animals, and fungi evolved from protists hundreds of millions of years ago

The Origin of Eukaryotes Combination of 2 processes 1.Internal membranes, ER, golgi and nuclear envelope evolved from inward folds of plasma membrane of ancestral prokaryotic cells –Membrane allowed cell to do more complex reactions in separate compartments 2.Existence of mitochondria and chloroplasts –Endosymbiosis: chloroplasts and mitochondria evolved from small symbiotic prokaryotes that lived within other, larger host cells

Symbiosis Symbiosis - relationship between 2 organisms of different species that live in close contact Symbiotic ancestors of mitochondria = aerobic bacteria –Ancestral host cell may have ingested these and the cells remained alive and performed CR in host cell Ancestors of chloroplast - same with photosynthesis Mitochondria evolved first

Evidence for Endosymbiosis Theory Mitochondria and chloroplasts are similar to prokaryotic cells –Contain DNA, RNA, ribosomes; resemble prokaryotes more than eukaryotes Mito and chloro copy own DNA and reproduce within host cell by a process resembling binary fission