Algae are a diverse group of photosynthetic organisms that are either protists or primitive aquatic plants. They vary greatly in size and structure from single-celled to multicellular forms over 70 meters long. While similar to plants in some ways like possessing chlorophyll and cell walls, algae differ in lacking true roots, stems, leaves and vascular tissue. They are classified into seven phyla based on pigments, food storage and cell wall composition, with the largest being the Chlorophyta (green algae), Phaeophyta (brown algae) and Rhodophyta (red algae). Algae play important ecological roles as primary producers and oxygen generators in many aquatic ecosystems.

1. ALGAE
Multicellular Protist or Primitive
Aquatic Plant?
Cyanobacteria
Plant-like
Protists

2. Algae

3. Algal Characteristics
• Vary in size from
nanoplankton (< 2 µm
cyanobacteria ) to Giant kelps
(> 70 m long). Possess a cell
wall.
• Contain pigments
• chlorophylls a, and many
often have another
chlorophyll, like b, c, or d
and accessory red, blue
and brown photosynthetic
pigments

4. Algae - What are they?
• Primitive plants
• No true roots, only attachment
structures (Holdfasts)
• Produce spores (not seeds)–
motile or non-motile
• Most have sexual and asexual
reproduction
• Non-vascular, do not possess
an internal transport system.

5. Algae vs. ‘REAL’
plants
Similarities and differences:
• Both are photoautotrophic
• Similar metabolic functions to higher
plants eg. photosynthesis
• different anatomical structures,
reproductive structures.
• different reproduction.
• No true roots, stems leaves.
• Non-vascular, therefore nutrient
uptake over surface. And wastes
washed away from surface by
aquatic environment

6. Classification - a few Algal Phyla
• Cyanophyta: Blue-green or Cyanobacteria.
Prokaryotic. Marine, FW and terrestrial.
• Pyrrophyta, Chrysophyta, Euglenophyta: Marine
and FW phytoplankton – Photosynthetic Protists.
KINGDOM PLANTAE:
• Rhodophyta: Red algae. Mostly marine.
• Phaeophyta: Brown algae. Mostly marine.
• Chlorophyta: Green algae. Marine, FW and
terrestrial.

7. The role of these pigments is to absorb light
- In water the problem is that red and violet wavelengths do not
penetrate the vertical column very well. So Chlorophylls do not
work well at greater depths. Algae that inhabit greater depths do so
with the help of accessory pigments, these algae take on a variety of
colours.

8. -Chlorophyta – Contain
Chlorophyll a + b. So green
wavelengths reflect. They store
their products of photosynthesis
as starch.
- Phaeophyta – Contain
Chlorophylls a + c as well as an
accessory pigment Fucoxanthin.
So yellow and brown
wavelengths reflect. Store food
as starch and as oil.
Rhodophyta - Contain
Chlorophyll a + (d) as well as
accessory pigment Phycobillins.
These phycobillins are
specialized for absorbing blue
light, which allows them to
inhabit the deepest depths.

9. Where do Algae live?
Marine habitats:
• seaweeds, phytoplankton
Freshwater habitats:
• streams, rivers, lakes
and ponds
Terrestrial habitats:
• stone walls, tree bark,
leaves, in lichens, on
snow

10. Marine Biomes

11. Freshwater habitats

12. Terrestrial habitats

13. How do algae function?
Photoautotrophs: 6C02 + 6H20 
C6H1206 + O2
• use carbon, light, and water
• produce chemical energy
(carbohydrates) and produce O2 as
a by-product.
• Basic storage products:
carbohydrates as starch or
converted to fats as oil
• Require nutrients: N, P and
minerals.

14. Why are ALGAE important?
Ecological importance of algae
a) Production of Oxygen as ‘by-
product’ of photosynthesis:
• All aerobic heterotrophic
organisms require O2,
• e.g. fungi and animals need O2, to
run cellular respiration to stay alive
b) Production of biomass:
• autotrophic organisms
- represent the base of the food
chain/web,
particularly in aquatic
environments.

15. Algal diversity
• Algae ARE NOT a single phylogenetic
grouping, but give rise to several independent
evolutionary lines. Our focus is on
“CHLOROPHYTA” as it is believed to give rise
to the terrestrial plants.
• Very diverse, very well adapted to certain
environments,
• Range from unicellular,  colonial 
multicellular
• e.g. marine, freshwater, terrestrial;
• often extreme habitats
• CHLOROPHYTES share Similarities to
true plants – Same two chlorophylls a
and b, Store products of photosynthesis
as starch, cell wall primarily made of
cellulose.

16. Algal construction types : Morphology
1. Unicellular algae
2. Colonies
3. Filaments
4. Multicellular

17. Unicellular algae
• ‘Microalgae’ - some may form colonies

18. Algal colonies
e.g. Chlorophyta: Volvox (Order Volvocales)
- 500-5000 cells per colony.
- Colonies spherical up to 1.5 mm diameter.
- Individual cells surrounded by a mucilaginous sphere
- marine and freshwater
http://www.youtube.com/watch?v=w8O4OolGcPg

19. Volvox colony – with Daughter colonies

20. Filamentous algae
• Unbranched filaments
• Branched filaments
• Different branches can have different
morphologies:

21. MULTICELLULAR - Macroscopic

22. Why are algae important?
• Primary producers, basis of food webs,
“FORESTS/GRASSES OF THE SEA”
• Pioneer Species: on rocky shores, mudflats,
hot springs, lichen communities, 'snow algae'
• O2 production and carbon fixation in aquatic
habitats.
• Rare autotrophic organisms in extreme
habitats.

23. Examples of ecological importance
• Red tides, other algal blooms
• Hot springs
• Kelp forests
• Rocky shore ecology
• Aquaculture

25. Cyanobacterial bloom

26. Extreme halophytes

27. Uses of Seaweeds
• Present
• Food
• Hydrocolloids and some
chemical substances
• Fertilizers
• Potential
• Source of
energy/compost by
digestion
• Waste-water treatment

28. Algae as human food
• Annual value is about US$6 billion
• Main market and production area is Asia
• “Mariculture” has become very important
• Main high-value species are ‘Nori’, ‘Kombu’ and
‘Wakame’ (Porphyra, Laminaria and Undaria)
• Mainly used as a subsidiary food: adding relish, taste
and 'feel' to food
• European and North American market presently very
small but has potential

29. CLASSIFICATION OF ALGAE
• SEVEN PHYLUM BASED ON
• COLOR
• TYPE OF CHLOROPHYLL
• FOOD-STORAGE SUBSTANCE
• CELL WALL COMPOSITION

30. Phylum Chlorophyta
• Green algae
• 7000 diverse species
• Biologist reason that green algae give
rise to land plants.
• Both green algae and land plants have
chlorophyll a and B as well as
carotenoids and store food as starch
• Both have walls made of cellulose

31. Phylum Phaeophyta
• 1500 species of Brown
algae
• Mostly marine and include
seaweed and kelp
• All are multicellular and large
(often reaching lengths of
147 feet)
• Individual alga may grow to a
length of 100m with a
holdfast, stipe and blade
• Used in cosmetics and most
ice creams

32. Phylum Rhodophyta
• 4000 species of RED Algae
• Most are marine
• Smaller than brown algae and are often
found at a depth of 200 meters.
• Contain chlorophyll a and C as well as
phycobilins which are important in
absorbing light that can penetrate deep
into the water
• Have cells coated in carageenan which is
used in cosmetics, gelatin capsules and
some cheeses

33. Phylum Euglenophyta
• 1000 species of
Euglenoids
• Have both plantlike
and animal-like
characteristics
• Fresh water

34. Other Phylum
Representatives
Diatoms – used in detergents,
paint removers, toothpaste
Dinoflagellates – red tides
Important in the
formation of
petroleum
products
Golden algae