Tài liệu Lục tảo pptx

Green algae Chlorophyta... • Type of reproduction sexual, asexual?. Cyanobacteria Cyanophyta• Prokaryotic, no cell organelles • Pigments: chlorophyll a, phycoerythrin + phycocyanin • On

Algae 2/3:

1 Unicelluar algae (various groups)

2 Green algae (Chlorophyta)

Unicellular algae

Figure 28.03x Euglena

Diatom

Dinoflagellate

Golden Algae

Unicellular algal groups

• Cyanophyta (Blue-green Algae;

prokaryotes)

• Diatoms

• Dinoflagellates

• Chrysophyta

• Chlorophyta (Green Algae)

• Rhodophyta (Red Algae)

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)

• 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 singleŠcelled protist

Conjugation

Diatoms

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

Figure 28.17x Diatom shell

Diatom Characteristics

• 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’)

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

Poisoning)

• Some species produce small amounts of light

by means of enzymes

Green Algae (Chlorophyta)

Chlorophyta - Green Algae

Green Algae - Characteristics

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

Chara

Volvox colony

Caulerpa

© D Stengel

Ulva and Enteromorpha

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 +

Ulva life-cycle: isomorphic