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 Include some prokaryotic and eukaryotic forms important in plant evolution

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

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

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

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

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

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

Cyanobacteria- akinetes +vegetative cells

Cyanobacteria with heterocysts+vegetative cells

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

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

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’

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

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.