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