Chapter 17 Protists. 17.1 Protists are the most diverse of all eukaryotes protists: eukaryotes that...
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Transcript of Chapter 17 Protists. 17.1 Protists are the most diverse of all eukaryotes protists: eukaryotes that...
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, spore1. 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 processes1. 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