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The Algae

The Algae. Lecture 2. Algae. The course will also cover algae Term algae is used to collectively refer to a wide range of simple oxygen-evolving photosynthetic organisms Algae is not a taxonomic group but used informally

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The Algae

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  1. The Algae Lecture 2

  2. Algae.. • The course will also cover algae • Term algae is used to collectively refer to a wide range of simple oxygen-evolving photosynthetic organisms • Algae is not a taxonomic group but used informally • Include some prokaryotic and eukaryotic forms important in plant evolution

  3. Main features of algae • Body is not specialized into root, stem & leaves • Photosynthesis occurs in thallus (body) • Attachment by rhizoids • No embryo formation • Gametes fuse in open waters • Zygote develops into new plant- no embryos stage • Reproductive structures not protected • Gametes produced within a single cell, not well protected by sterile envelope as in plants

  4. Where found? • Mostly aquatic (watery environments) • Marine • Freshwater • Floating- planktonic (have floating structures) • Attached to objects- benthic • Terrestrial (wet soils) • Have mechanisms to survive drying

  5. Morphological diversity • Different body types • Some unicells- single cells with/ without flagella • Some filamentous- cells forming chains • Some colonial- several cells attached together • Coenobia- fixed number of cells in a colony • Siphonaceous- tubular structures not divided into cells; have many nuclei (coenocytic) • Parenchymatous- body made up of cells like higher plants; large (macro) algae

  6. Reproductive diversity • Both sexual and asexual reproductive • Asexual • Fragmentation- breaking away • Spore formation- dispersal structure • Sexual- fusion of gametes • Isogamy- fusion of equal size motile gametes • Anisogamy- gametes unequal, motile • Oogamy- small motile, male gamete fuse with large stationary gamete

  7. Algal groups • 1) Blue-green algae (cyanophyta or cyanobacteria) • Oldest group • Earliest Oxygen producing, photosynthetic plants • Prokaryotic as in bacteria- no organelles • No chloroplasts • Chlorophyll a and other blue (phycocyanin) pigments hence the name blue-green algae • Cell wall similar to bacteria- murein wall • Asexual reproduction by mitosis, fragmentation • No sexual reproduction known

  8. Blue-greens… • May be enclosed in a sheath • Unicells or colonies • Filamentous- cells in filaments surrounded by a sheath • Cells in filament may be differentiated into vegetative cells, akinetes (spore) and heterocysts ( nitrogen fixing cell) eg Anabaena, Nostoc • Many are important in nitrogen fixation like some bacteria

  9. Cyanobacteria- akinetes +vegetative cells

  10. Cyanobacteria with heterocysts+vegetative cells

  11. Blue-green algae… • Many blue greens form blooms that are toxic • Kill livestock, fish and humans • Important in the evolution of living organisms and in endosymbiont theory and the origin of chloroplasts and eukaryotic cell

  12. 2) Green algae- Chlorophyta • Largest, most common and diverse group especially in freshwaters • Found everywhere in Botswana • Unicels, filamentous, colonial &parenchymatous • Chlorophyll a &b and carotenoids • Cell wall mainly cellulose • Stored food product is starch • All above also found in plants • Show asexual and sexual reproduction • Life cycles show alternation of generations

  13. 3) Other algal groups • a)Diatoms • Silica cell wall • Glasshouse shell • b)Euglenoids • Unicelluar with flagellar • Soft cell covering, euglenoid movement • c)Brown algae- have chl a & c and brown pigments • d)Red algae- chl a and d and red pigments • Brown and red algae mostly marine known as macroalgae or ‘seaweeds’

  14. Economic importance of algae • Primary producers- contribute 50-60% of primary production on earth especially in aquatic environments (feed fish etc) • May grow into large numbers in nutrient –rich waters causing algal blooms or water blooms or ‘red tides’ • Some of these are poisonous to humans and aquatic organisms • Used as food or fertilizers

  15. Algae: Economic importance • Useful cps are extracted from cells walls of algae used as thickening agents in foods, cosmetics, media • ice creams, lotions, creams, microbiological media • Remains of dead algae (diatoms) form diatomaceous earth with many uses such as filters in water and beer filtration, reflective road signs, abrasives in tooth pastes, cleaning and polishing materials.

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