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 Photosynthesis occurs in thallus (body)
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… 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. Blue-green algae… Many blue greens form blooms that are harmful
May kill livestock, fish and humans
They are important in the evolution of living organisms
Also in endosymbiont theory and the origin of chloroplasts and eukaryotic cell

10. 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
Chlorophylls, cellulose and starch also found in plants
Show asexual and sexual reproduction
Life cycles show alternation of generations

11. 3) Other algal groups of importance
a) Diatoms
Silica cell wall (sand cell wall)
Form a 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’ , produce very useful cpds

12. Economic importance of algae
Primary producers- contribute 50-60% of primary production on earth especially in aquatic environments (feed fish etc)
Some are nitrogen fixers
May grow in 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
Some used as food or fertilizers

13. 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:
water filters,
beer filtration,
reflective road signs,
abrasives in tooth pastes,
cleaning and polishing materials.