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Unicellular algal groups
• Cyanophyta (Blue-green Algae; prokaryotes)
• Diatoms
• Dinoflagellates
• Chrysophyta
• Chlorophyta (Green Algae)
• Rhodophyta (Red Algae)
Occurrence of Unicellulars• Phytoplankton (freshwater, marine)• Benthic microalgae• Epiphytic (on other algae) or on rocks,
sediments, etc.• Terrestrial algae (walls, trees, etc)• Symbioses: in lichens, root nodules, marine
sponges• Parasites (e.g. heterotropic dinoflagellates)• Hot springs• Ice algae (‘red snow’)
How to distinguish between different unicellular algae?
• Pigments?
• Flagella: types of movement?
• Type of reproduction (sexual, asexual)?
• Life history?
• Cell structure?
• Formation of colonies or filaments?
Cyanobacteria (Cyanophyta)
• = ‘Blue-green Algae’• Prokaryotic, no cell organelles• Pigments: chlorophyll a, phycoerythrin +
phycocyanin• Only asexual reproduction• Some can fix atmospheric Nitrogen• Can form blooms• In extreme habitats (e.g. hot springs)• In lichens
Diatom Characteristics
• 2 orders: • Centrales: radial symmetry (centric diatoms)• Pennales: bilateral symmetry (pennate diatoms)
• Cell wall consists of 2 shells• Large top shell (‘lid’): Epitheca• Small bottom shell (‘box’): Hypotheca• Cell wall contains silica
Diatom Characteristics II
• Forming cysts as resting stages if
conditions are unfavourable
• Accessory pigments: golden coloured
Dinoflagellate Characteristics
• Generally unicellular, may form colonies or filaments
• Chlorophyll a and a range of other pigments giving lots of different colours
• Numerous colourless genera (animal-like): heterotrophic!
• 2 flagella: • one apically inserted
• one in equatorial groove (=‘horizontal slit’)
Dinoflagellates
Importance:
• Harmful algal blooms
• Toxic algal blooms: shellfish poisoning
• Parasites: fish and copepodes
• Symbionts: sponges
Dinoflagellates: Red Tides• often the cause of “red tides” or blooms of
toxic or non-toxic cells
• blooms may cause mass mortalities of marine and freshwater organisms
• contain toxins that are accumulated by shellfish and cause PSP (Paralytic Shellfish Poisoning)
• Some species produce small amounts of light by means of enzymes
Green Algae (Chlorophyta)
• About 7000 species
• 3 Classes: • Chlorophyceae• Charophyceae • Prasinophyceae
• Some relatively closely related to land plants:(Charophyceae)
Chlorophyta - Green Algae
• Morphological types:• unicellular • multicellular • colonial • coenocytic (one large cell
with no cross walls)
• Some symbiotic (e.g. in lichens)
• Asexual and sexual reproduction
Green Algae - Characteristics
• Pigments: • Chlorophylls a and b, • ß-carotene and various xanthophylls
• Food reserves: • true starch, fats and oils
• Eukaryotic algae: • membrane-bound organelles
• Flagella: • 2 or 4, • apically inserted, • smooth
Distribution of Green Algae
• >90% freshwater, some marine
• planktonic in ocean and freshwater
• ‘terrestrial’ environments
• in lichens = symbiosis of alga + fungus;
• exchange of nutrients between partners
Distribution and habitats• Common in ponds, ditches etc.
• Attached to rocks
• May be free floating
• Often in brackish water
• Shallow, nutrient-rich water
• Important marine algae in tropics
Ulva and Enteromorpha• 2 genera of marine or
brackish-water green algae• Ulva:
• flat (“Sea Lettuce”)
• 2 layers thick
• Enteromorpha• tubular
• 1 layer thick• No true tissues • cells are almost exactly the
same throughout the thallus
Ulva and Enteromorpha
• Both reproduce sexually and asexually
• Fast growth rates
• High metabolic rates
• Fast nutrient uptake
• Occupy new spaces after disturbances
• May form Green Tides:• High light• High nutrients (e.g. sewage)
Enteromorpha + Ulva: Reproduction
• Asexual reproduction: Bi-flagellate zoospores
• Sexual reproduction: • Gametophytes (1n) form biflagellate
isogametes; fuse in pairs -> germinate -> form sporophyte (2n).
• Sporophyte cells undergo meiosis -> form quadriflagellate zoospores (1n) -> release -> form the gametophytes (1n).
• Sporophyte isomorphic to gametophyte except that it is diploid.
Life cycle of Ulva + Enteromorpha• Diphasic:
Sporophyte and Gametophyte
• Isomorphic:
S. and G. morphologically similar
• Isogamous:
F and M gametes morphologically similar
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