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

2. Unicellular algae

3. Euglena

4. Diatom

5. Dinoflagellate

6. Golden Algae

7. Unicellular algal groups
Cyanophyta (Blue-green Algae; prokaryotes)
Diatoms
Dinoflagellates
Chrysophyta
Chlorophyta (Green Algae)
Rhodophyta (Red Algae)

8. 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’)

9. 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?

10. 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

11. Cyanobacteria bloom

12. Terrestrial environments

13. Extreme halophytes

14. Hot springs

16. Spirogyra Conjugation

17. Diatoms

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

19. Figure 28.17x Diatom shell

20. 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

21. Diatom Characteristics II
Forming cysts as resting stages if conditions are unfavourable
Accessory pigments: golden coloured

22. Dinoflagellates

23. 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’)

24. Dinoflagellates Importance: Harmful algal blooms
Toxic algal blooms: shellfish poisoning
Parasites: fish and copepodes
Symbionts: sponges

25. 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

26. Green Algae (Chlorophyta)
About 7000 species
3 Classes:
Chlorophyceae
Charophyceae
Prasinophyceae
Some relatively closely related to land plants:
(Charophyceae)

27. 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

28. 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

29. 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

30. 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

31. Examples of Green Algae
Chlamydomonas
Chara
Volvox
Caulerpa
Codium
Ulva
Enteromorpha

32. Chara

33. Volvox colony

34. Caulerpa

35. Codium
© D. Stengel

36. Ulva and Enteromorpha 2 genera of marine or brackish-water green algae
flat (“Sea Lettuce”)
2 layers thick
Enteromorpha
tubular
1 layer thick
No true tissues
cells are almost exactly the same throughout the thallus

37. 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)

38. 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.

40. Life cycle of Ulva + Enteromorpha
Diphasic:
Sporophyte and Gametophyte
Isomorphic:
S. and G. morphologically similar
Isogamous:
F and M gametes morphologically similar

41. Ulva life-cycle: isomorphic