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CYANOBACTERIA, DINOPHYTA, BACILLARIOPHYCEAE, & COSCINODISCOPHYCEAE Objective Today we will examine members of the Cyanobacteria, Dinophyta, Bacillariophyceae, Coscionodiscophyceae and Magnoliophyta. We will become familiar with aspects of their diversity, variation in morphology, and special thallus features. Notebook Requirements: 12 drawings Phytoplankton (treasure hunt): Drawings: Draw 3 Diatoms Draw 3 Dinoflagellates Note: For taxonomy, you only need to include Division, Class (diatoms) and Genus (make best guess from drawings on lab handout provided) Questions: Define each term and suggest its function: Raphe Undulopodium Frustule Auxospore Girdle Planozygote Epicone Hypnozygote Hypocone Trichocysts 1. Label the ploidy of diatoms & dinoflagellates. What type of life history do each have? 2. Describe asexual reproduction in diatoms. What triggers sexual reproduction in diatoms? 3. What triggers asexual and sexual reproduction in dinoflagellates? 4. What types of strategies do diatoms and dinoflagellates use to stay in the photic zone? Cyanophyta: Drawings: Draw Spirulina (live) Draw Oscillatoria (live) Draw Anabaena and Nostoc (live) o Label: heterocysts, akinetes Draw Tolypothrix (prepared slide) o Label and define: false branching Draw Stigonema (prepared slide) o Label and define: true branching Bonus: Look for and label hormogonia (notify TA if you find any) Questions: Define each term and suggest its function: Filament Trichome Sheath Heterocyst Hormogonia Akinete Gas vacuoles Carboxysome 1. Under what conditions are heterocysts and akinetes formed? 2. Describe the process of nitrogen fixation. Why does it need to occur in a specia lized environment? Name the enzyme involved. 3. Besides heterocyst formation, what other ways can some Cyanophyta spatially separate the enzyme used to fix atmospheric nitrogen from oxygen? 4. Describe the fate of an akinete once it is formed within the trichome. Are akinetes positively or negatively buoyant? Introduction - Cyanobacteria Although the exact number of species is debatable, “Algaebase.org” estimates there to be about ~4000 species. Being Bacteria, the Cyanobacteria lack membrane bound organelles. However, given that they have chlorophyll a and release oxygen through photosystems I & II, we will consider them to be “algae.” The Cyanobacteria (also called bluegreen algae) are the oldest organisms to give off oxygen via Photosystems I and II and are estimated to have existed for between 2.2 and 3.5 billion years; fossil stromatolites (layered rocks formed by accretion of minerals around cells) date back to the Precambrian period. The Cyanobacteria are ubiquitous, occurring in both seawater and freshwater, on unconsolidated substrata—endolithically in deserts and in Antarctic ice, and epilithically on tropical intertidal limestone. They are important fixers of nitrogen, contibute to toxic red tides, and were some of the first organisms to give off oxygen, thus playing a pivotal role in creating Earth’s oxidizing atmosphere. Many species possess specialized thick-walled cells called heterocysts that aid in nitrogen fixation by separating the site of nitrogen fixation from sources of oxygen. Systematics - CYANOPHYTA Orde r Thallus Characteristics Examples Chroococcales Unbranched filaments fragmentation, hormogonia production, no specialized cells Spirulina Oscillatoriales Unbranched filaments fragmentation, hormogonia production, no specialized cells Oscillatoria, Nostocales Unbranched filaments Branched filaments May have heterocysts, hormogonia and akinetes Nostoc, Anabaena, Tolypothrix Stigonema LIVE SPECIMENS - CYANOPHYTA Spirulina Anabaena Filamentous, common in lakes with high soda, high pH, spiraled trichomes. Planktonic, anatoxin (neurotoxin) hepatoxin, heterocysts visable, negative phototaxis— can steer the tip of the filament towards light. Nostoc Often associated with fungi in lichens, filamentous, can form colonies, akinetes midway between heterocysts. PREPARED SPECIMENS - CYANOPHYTA 3 Tolypothrix Stigonema Planktonic, often in freshwater lakes, false branching at heterocysts Inhabits moist rocks and soil, often associated with fungi in lichens, filaments can be multiple cells in width (multiseriate), exhibits true branching 4 5 6 7 8 9 10 11 12