1 / 15

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

damia
Télécharger la présentation

The Algae

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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.

More Related