Class 11 Biology: A Comprehensive Guide to Algae (With NCERT Notes & Mind Maps)

  

Algae

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

1. Vegetative Reproduction:

   • By fragmentation.
   • Each fragment develops into a new thallus.

2. Asexual Reproduction:

   • Through spores, primarily zoospores (flagellated and motile).

3. 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

1. 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.

2. 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.

3. 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

 Also Read:

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