Algae-General characteristics and Classification




ALGAE-

GENERAL CHARACTERSTICS

  1. Algae are the simplest multicellular plants. Some are unicellular eg. Chlamydomonas
  2. Pant body: known as Thallus and they are avascular
  3. Habitat: Algae are usually aquatic, either freshwater or marine and some are terresterial.
  4. Algae are eukaryotic thallophytes.
  5. Algae are photoautotrophs.
  6. Storage form of food: Starch
  7. Reproduction: Algae reproduce either by vegetative, asexual or sexual method
  8. Vevetative method: fragmentation, hormogonia
  9. Asexual spore: zoospores, aplanospores, hypnospores, akinetes, azygospore
  10. Sexual method:  isogamous, anisogamous, and oogamous gametic fusion

CLASSIFICATION OF ALGAE

On the basis of photosynthetic pigments algae classified into three classes.

  1. Chlorophyceae (green algae)
  2. Phaeophyceae (brown algae)
  3. Rhodophyceae (red algae).

 1. Chlorophyceae (Green algae)

General characterstics

  • It is the largest class of algae
  • They are commonly known as green Algae.
  • Photosynthetic pigments: They possesses chlorophyll a, chlorophyll b and small amount of β-carotenoids.
  • The chloroplasts shows various shape ie. Spiral shape in Spirogyra, cup shaped in Chlamydomonas, star shaped in Zygnema, girdle shaped in Ulothrix
  • Habitat: Mostly freshwater (Spirogyra, Oedogonium, Chlamydomonas, Volvox, etc), some are marine (Sargassum, Laminaria, etc) and some are parasitic (Polysiphonia, Harvevella, Cephaleuros)
  • Distribution: they are cosmopolitan in distribution
  • They are unicellular as well as multicellular.
  • Each cell is eukaryotic
  • Thalllus: their body structure, shape and size varies.

Chlamydomonas: unicellular free living

Volvox: colonial form

Spirogyra: multicellular, unbranched filamentous form

Ulva: multicellular, parenchymatous form

  • Storage form of food: Starch
  • Pyrenoids stores starch
  • Cell wall has two layer: outer layer composed of pectose and inner layer is composed of cellulose
  • Reproduction: vegetative, asexual and sexual method
  • Vegetative : fragmentation
  • Asexual: asexual sopre (akinete, aplanospore, azygospore)
  • Sexual: isogamous, anisogamous, oogamous type gametic fusion

2. Phaeophyceae (Brown algae)

General characteristics

  • Pheophyceae are called commonly known as brown algae
  • Photosynthetic pigments: They possesses brown colored photosynthetic pigments fucoxanthin and β-carotenoids in addition to chlorophyll a and c.
  • Habitat: They are almost marine, very few are fresh water eg.
  • Thallus: they are multicellular brown algae. No unicellular and colonial (motile or non-motile) brown algae till known.
  • Storage form of food: laminarin starch, manitol (alcohol) and some store iodine also.
  • Reproduction: vegetative, asexual and sexual methods
  • Vegetative: fragmentation.
  • Asexual: asexual spores (motile zoospores).
  • Sexual: isogamous or oogamous type gametic fusion.

 

3. Rhodophyceae (Red algae)

General characteristics

  • Rhodophyceae are commonly known as Red Algae
  • Photosynthetic pigments: They possesses Red colored photosynthetic pigments r-phycocyanin and r-phycoerythrin along with chlorophyll a, d, xanthophyll and β-carotenoid
  • Habitat: They are aquatic, mostly marine. Some are freshwater e.g. Batrachospermum.
  • Thallus: Red algae show a variety of life forms-

Unicellular- Porphyridium,

multicellular- Goniotrichum,

Parenchymatous- Porphyra,

unicellular colonies-Chroothece,

  • Storage form of food: Floridean starch and floridosides sugar.
  • Reproduction: vegetative, asexual and sexual mode
  • Vegetative: fragmentation
  • Asexual reproduction: non- motile spores( akinete, aplanospore, azygospore)
  • sexual reproduction: Oogamous.
  • Some species shows Alternation of generations in their life cycle.