Introduction to Algae
- Characteristics:
- Chlorophyll-bearing, simple, thalloid, and autotrophic organisms.
- Largely aquatic, found in freshwater and marine environments.
- Can also inhabit moist stones, soils, wood, and live in symbiotic relationships (e.g., lichens with fungi, on sloth bears).
Forms and Sizes of Algae
- Variable Forms:
- Colonial forms like Volvox.
- Filamentous forms like Ulothrix and Spirogyra.
- Massive marine forms like kelps.
Reproduction in Algae
Vegetative Reproduction:
- By fragmentation.
- Each fragment develops into a new thallus.
Asexual Reproduction:
- Through spores, primarily zoospores (flagellated and motile).
Sexual Reproduction:
- Isogamous: Fusion of similar-sized gametes (e.g., Ulothrix).
- Anisogamous: Fusion of dissimilar-sized gametes (e.g., species of Eudorina).
- Oogamous: Fusion of a large non-motile female gamete and a smaller motile male gamete (e.g., Volvox, Fucus).
Importance of Algae
Ecological Role:
- Major contributors to carbon dioxide fixation through photosynthesis.
- Increase dissolved oxygen levels in their environment.
- Primary producers in aquatic food cycles.
Economic Importance:
- Edible species like Porphyra, Laminaria, and Sargassum.
- Production of hydrocolloids such as algin (from brown algae) and carrageen (from red algae).
- Agar from Gelidium and Gracilaria used in microbial culture, ice-cream, and jelly production.
- Chlorella as a protein-rich food supplement, even for space travelers.
Classes of Algae
Chlorophyceae (Green Algae):
Characteristics:
- Unicellular, colonial, or filamentous.
- Green due to chlorophyll a and b.
- Chloroplasts can be discoid, plate-like, reticulate, cup-shaped, spiral, or ribbon-shaped.
- Storage bodies (pyrenoids) contain protein and starch.
- Cell wall composed of cellulose and pectose.
Reproduction:
- Vegetative by fragmentation.
- Asexual by flagellated zoospores.
- Sexual can be isogamous, anisogamous, or oogamous.
Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara.
Phaeophyceae (Brown Algae):
Characteristics:
- Mostly marine.
- Size ranges from simple filamentous forms to large kelps.
- Contain chlorophyll a, c, carotenoids, and fucoxanthin (xanthophyll pigment).
- Store food as laminarin or mannitol.
- Cell wall has cellulose and a gelatinous algin coating.
- Structure includes holdfast, stipe, and frond.
Reproduction:
- Vegetative by fragmentation.
- Asexual by biflagellate zoospores.
- Sexual can be isogamous, anisogamous, or oogamous with pyriform gametes.
Examples: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus.
Rhodophyceae (Red Algae):
Characteristics:
- Predominantly marine, especially in warmer regions.
- Red due to r-phycoerythrin pigment.
- Can live in well-lit regions or deep ocean areas.
- Multicellular with complex body structures.
- Store food as floridean starch (similar to amylopectin and glycogen).
Reproduction:
- Vegetative by fragmentation.
- Asexual by non-motile spores.
- Sexual reproduction by non-motile gametes.
Examples: Porphyra, Polysiphonia, Gelidium, Gracilaria.
Visual Summary (Mind Map)
Algae
Characteristics
- Chlorophyll-bearing
- Thalloid
- Autotrophic
- Aquatic
Forms and Sizes
- Colonial: Volvox
- Filamentous: Ulothrix, Spirogyra
- Massive: Kelps
Reproduction
- Vegetative: Fragmentation
- Asexual: Zoospores
- Sexual:
- Isogamous: Ulothrix
- Anisogamous: Eudorina
- Oogamous: Volvox, Fucus
Importance
- Ecological: CO2 fixation, Oxygen production, Primary producers
- Economic: Food, Hydrocolloids (algin, carrageen), Agar, Chlorella
Classes
- Chlorophyceae (Green Algae)
- Characteristics: Chlorophyll a, b, pyrenoids, cellulose cell wall
- Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara
- Phaeophyceae (Brown Algae)
- Characteristics: Chlorophyll a, c, fucoxanthin, laminarin/mannitol storage
- Examples: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus
- Rhodophyceae (Red Algae)
- Characteristics: r-phycoerythrin, floridean starch
- Examples: Porphyra, Polysiphonia, Gelidium, Gracilaria
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