Chapter 21 PROTISTA

A. The Basal Eukaryotes Includes several distantly related groups; believed to be the earliest unicellular eukaryotes to diverge. 1. Basal Eukaryotes Lacking Mitochondria Ancestors of these organisms may have diverged before the endosymbiotic event that gave rise to mitochondria.

] Parabasalia - flagellated organisms found only in association with animals. Trichomonas vaginalis causes the STD trichomoniasis. Trichonympha live in termites; contain bacteria that digest cellulose. ] Diplomonadida - flagellated organisms found in stagnant fresh water or in intestines. Giardia lamblia causes “hiker’s diarrhea”.

2. Basal Eukaryotes With Mitochondria ] Amoebae - aquatic organisms that use pseudopodia to move & to feed. Amoeba proteus ] Acellular slime molds - heterotrophic organisms that exist as an amoeboid mass called a plasmodium. Physarum

] Cellular slime molds - heterotrophic organisms that exist as single cells. When food is lacking, cells aggregate to form a multicellular slug.

] Euglenida - organisms that possess an anterior chamber from which one or two flagella emerge. Euglena is a pond dwelling organism; has both plant & animal characteristics.

] Kinetoplastida (trypanosomes) - flagellated organisms; have a single, large mitochondrion containing a kinetoplast (houses extracellular DNA). Trypanosoma brucei causes African sleeping sickness; transmitted to humans by bite of tsetse fly.

B. The Alveolates Includes protists that have alveoli beneath the cell membrane. 1. Dinoflagellates - organisms possessing a pair of flagella that cause the cell to spin as it swims; major components of phytoplankton. Gonyaulax “blooms” cause red tides. Pfiesteria piscicida has 24 stage life cycle.

2. Ampicomplexans - obligate parasites of animals; all possess an apical complex & have complex life cycles. Plasmodium causes malaria; transmitted to humans by mosquitoes. Toxoplasma gondii causes toxoplasmosis; pregnant woman can become infected via cat feces & pass disease to fetus.

3. Ciliates - organisms that move by means of cilia. Paramecium Didinium

C. The Stramenopiles Includes protists that have unique flagella & laminarin; photosynthetic stramenopiles have pigments not found in plants. 1. Water molds (oomycetes) - absorb nutrients from their surroundings. Plasmopara viticola causes downy mildew of grapes. Phytophthora infestans causes late blight of potatoes.

2. Diatoms - organisms that have two- part silica walls called frustules; major components of phytoplankton. Abrasiveness of frustules makes diatoms useful ingredients in polishes.

3. Brown algae - large, multicellular seaweeds; brown color is due to the photosynthetic pigment fucoxanthin. Giant kelp 4. Golden algae - most are unicellular; golden color is due to carotene & xanthophyll photosynthetic pigments. When light or nutrient supplies dwindle, many will consume bacteria or diatoms.

D. The Red Algae Primarily multicellular; have photosynthetic pigments called phycobilins. Useful red algal products include: F agar - used as a culture medium for microbes, and to thicken ice cream & yogurt. F carageenan - used to stabilize paints, cosmetics & creamy foods.

E. The Green Algae Includes unicellular, multicellular & colonial autotrophs that resemble plants. Plant-like characteristics: F use chlorophyll a & b F store starch F have cell walls containing cellulose F most exhibit alternation of generations

Life cycle of the sea lettuce, Ulva

Green algae differ from plants: F most have pyrenoids (regions in chloroplasts that store starch) F lack true stems, roots & leaves Spirogyra - multicellular filaments containing spiral- shaped chloroplasts. Volvox - colonial organism consisting of 500 to 600,000 biflagellate cells.