|21.1 -Kingdom Protista Lies at the Crossroads Between the Simpler and the Complex
1. Most protista are unicellular eukaryotes; a few are multicellular.
2. Some protista may resemble early eukaryotes or more complex plants, animals, and fungi.
3. Classification of protista is changing as RNA and DNA sequence data are considered along with traditional traits.
4. The basal eukaryotes include protista that may reveal stages in the evolution of endosymbiont bacteria into mitochondria. They may be free-living or parasitic.
5. Basal eukaryotes lacking mitochondria include Giardia lamblia, which exists as a nonmotile, thick-walled cyst or a flagellated feeding form, and Parabasalia, some of which cause amoebic dysentery.
6. The acellular and cellular slime molds, along with some amoebae, Euglenida, and Kinetoplastida, represent the diversity of basal eukaryotes that have mitochondria.
21.2 -The Alveolates Include Dinoflagellates, Apicomplexa, and Ciliates
7. The alveolates share flattened sacs beneath the cell membrane and tubular mitochondrial cristae.
8. Dinoflagellates have two different-sized flagella at right angles that generate a whirling movement. Many have outer plates made of cellulose.
9. The apicomplexa are obligate parasites of animals. They share an apical complex of organelles that helps them attach to or penetrate host cells. Apicomplexa cause malaria and toxoplasmosis.
10. The ciliates are complex cells with cilia, food and contractile vacuoles, trichocysts, and two types of nuclei.
21.3 The Stramenopiles Include Water Molds, Diatoms, and Some Algae
11. The stramenopiles are diverse organisms that have unique types of flagella, laminarin, and photosynthetic pigments not found in plants.
12. The water molds are filamentous heterotrophs that live in moist or wet environments. Some are pathogens of plants.
13. Diatoms are microscopic phytoplankton with silica walls called frustules.
14. Fucoxanthin colors brown algae, which are large, multicellular seaweeds. The golden algae, which may be related to the brown algae, are photosynthetic but can eat other microorganisms when light or nutrient supplies decline.
21.4 The Red Algae Contain Unique Photosynthetic Pigments
15. Like plants, red algae have cellulose cell walls and chlorophyll a. Red algae produce phycobilin pigments that expand their photosynthetic range.
16. Red algae provide products such as agar and carageenan.
21.5 The Green Algae
17. Green algae are aquatic, store carbohydrates as starch, are photosynthetic and use the same pigments as plants. Many have alternation of generations. Unlike plants, green algae lack true roots, stems, and leaves, and they have less specialized cells.
18. The green algae have diverse body forms, ranging from microscopic, one-celled organisms to large, multicellular seaweeds.