Algae 2/3: 1. Unicelluar algae (various groups) 2. Green algae (Chlorophyta)

Algae 2/3:

1. Unicelluar algae (various groups)

2. Green algae (Chlorophyta)

Unicellular algae

Euglena

Figure 28.03x Euglena

Diatom

Dinoflagellate

GoldenAlgae

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

Cyanobacteria bloom

Terrestrial environments

Extreme halophytes

Hot springs

Figure 28.3 Euglena: an example of a single–celled protist

SpirogyraConjugation

Diatoms

Figure 28.17 Diatoms: Diatom diversity (left), Pinnularia (left)

Figure 28.17x Diatom shell

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

Dinoflagellates

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

Examples of Green Algae

• Chlamydomonas

• Chara

• Volvox

• Caulerpa

• Codium

• Ulva

• Enteromorpha

Chara

Volvox colony

Caulerpa

Codium

© D. Stengel

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

Ulva life-cycle: isomorphic