“Plant-Like” Protists:

1. “Plant-Like” Protists: Unicellular Algae

2. Unicellular Algae • Algae are • photosynthetic protists whose chloroplasts support food chains in • freshwater and • marine ecosystems. • Many unicellular algae are components of plankton, the communities of mostly microscopic organisms that drift or swim weakly in aquatic environments. • Chlorophyll and accessory pigments allow algae to harvest and use energy from sunlight. • Both give algae a wide range of colors

3. Unicellular Algae • Unicellular algae include: • dinoflagellates, with • two beating flagella and • external plates made of cellulose, • diatoms, with glassy cell walls containing silica, and • green algae, which are • unicellular in most freshwater lakes and ponds, • sometimes flagellated, such as Chlamydomonas, and • sometimes colonial, forming a hollow ball of flagellated cells as seen in Volvox.

4. Phylum Pyrrophyta - Dinoflagellates • Half are photosynthetic, half are heterotrophs • Two flagella • Reproduce asexually by binary fission • Some luminescent/give off light • Only eukaryote with no histones to help store DNA • Can cause red tides

5. Phylum Bacillariophyta – Diatoms • Most abundant organisms on Earth • Thin, silicon cell walls used to make glass

6. Phylum Euglenophyta - Euglena • “Plant-like” protists that have two flagella but no cell wall • Red eye-spot – helps organism find sunlight to power photosynthesis • Phototrophic autotroph or heterotroph (absorb nutrients in decayed organic material) • Pellicle – cell membrane • Reproduce asexually by binary fission

7. Euglena Anatomy Chloroplast Carbohydrate storage bodies Gullet Pellicle Contractile vacuole Nucleus Flagella Eyespot

8. Phylum Chrysophyta • Mostly solitary • Yellow-green and golden-brown algae • Gold-colored chloroplasts • Cell walls contain pectin rather than cellulose; others can have both pectin and cellulose • Reproduce asexually and sexually • Store oil, not starch

9. Ecology of Unicellular Algae • Helpful: • Phytoplankton – diatoms and dinoflagellates • 70% of photosynthesis occurs in ocean • Symbiosis – corals and dinoflagellates – Tridacha gigas (clam) and dinoflagellates • In both cases, algae provide food to the animal

10. Ecology of Unicellular Algae • Harmful: • Algae “blooms” – dangerous toxin produced by algae – shellfish eat the algae and eat the toxin = people can’t eat it • Dinoflagellate Gonyaulx – red tide

11. “Fungus-like” Protists • Heterotrophs that absorb nutrients from dead or decaying matter. Unlike true fungi, “fungus-like” protists have centrioles and lack chitin in cell walls • Recyclers of dead organisms

12. Slime Molds • Slime molds • resemble fungi in appearance and lifestyle, but • are more closely related to amoebas. • The two main groups of these protists are • plasmodial slime molds (aka acellular slime molds) and • cellular slime molds.

13. Slime Molds • Play key roles in recycling organic material • 3 Phyla of slime molds • Phylum Myxomycota (plasmodial) • Phylum Acrasiomycota (cellular) • Phylum Oomycota

14. Phylum Myxomycota • Plasmodial slime molds (aka acellular slime molds) • Begin life as amoeba-like cell, called plasmodia, that contain thousands of nuclei but only one cell membrane • Plasmodia may reach several meters in diameter • Form fruiting bodies • Produce haploid spores which germinate into flagellate cells which fuse to produce the diploid “amoeba”

15. Phylum Acrasiomycota • Cellular slime molds • Begin life as amoeba-like cells • When food begins to run out, then form colonies and produce a fruiting body which produces spores • Spores “hatch” into amoeba-like cells

16. Phylum Oomycota • Water molds • Thrive on dead or decaying organic matter in water and are plant parasites on land • Hyphae – thin filaments • A water mold caused the potato famine in Ireland in 1840s