Lecture Notes on Algae, Bryophytes, and Pteridophytes

Algae

• Definition: Slimy green layer found on rocks near the sea; autotrophic organisms.
• Types:
  • Unicellular: e.g., Chlamydomonas
  • Colonial: e.g., Volvox
  • Filamentous: e.g., Spirogyra
  • Massive Plant Bodies: e.g., Laminaria
• Reproduction:
  • Vegetative: Through fragmentation (each fragment develops into a new organism).
  • Asexual: Via spores (e.g., zoospores).
  • Sexual:
    • Can be isogamous (similar size gametes) or anisogamous (different size gametes).
    • Isogamous: Both gametes flagellated (Chlamydomonas) or non-flagellated (Spirogyra).
    • Anisogamous: Larger non-motile female gamete fuses with smaller motile male gamete.
• Functions: Carbon dioxide fixation, increased dissolved oxygen, food source for aquatic organisms, commercial uses (e.g., agar in ice creams).
• Classification:
  • Chlorophyceae (Green Algae): e.g., Chlamydomonas, Volvox, Spirogyra.
  • Phaeophyceae (Brown Algae): e.g., Laminaria, Hechtokopytis.
  • Rhodophyceae (Red Algae): e.g., Polysiphonia, Gracilaria.

Bryophytes

• Overview:
  • Non-vascular land plants, often found in damp, shady locales.
  • Called amphibians of the plant kingdom due to dependence on water for reproduction.
• Structure:
  • Plant Body: Thallus-like, anchored by rhizoids, lacks true roots/stems/leaves.
  • Gametophyte Phase: Main body is haploid; produces gametes.
  • Male gametes produced in Antheridia, female in Archegonia.
• Reproduction:
  • Asexual: Via fragmentation and gemmae (asexual buds).
  • Sexual: Fertilization occurs in water, forming a zygote which develops into a sporophyte (dependent on gametophyte).
• Types:
  • Liverworts: Found in moist areas; reproduce both sexually and asexually.
  • Mosses: Dominant gametophyte stage; reproduce through fragmentation and budding.
• Uses:
  • Peat formation for fuel, soil erosion prevention, colonizers of bare rocks, ecological importance.

Pteridophytes

• Overview: First terrestrial plants with vascular tissues, true roots, stems, and leaves. Found in damp places.
• Structure:
  • Sporophyte Dominance: Main plant body is diploid, produces spores in sporangia.
• Reproduction:
  • Sporophytes produce spores that germinate into gametophytes (prothallus).
  • Male and female organs present, gametes fuse to form a zygote.
• Types:
  • Homospory: One type of spore.
  • Heterospory: Two types of spores (megaspores for female, microspores for male).
• Lifecycle: Alternation of generations between sporophyte and gametophyte phases.

Gymnosperms

• Definition: Plants with exposed ovules, first to have seeds.
• Structure:
  • Usually have tap roots; may associate with fungi.
  • Leaves adapted to reduce water loss (e.g., needle-like leaves).
• Reproduction:
  • Male and female cones produce pollen grains and ovules, respectively.
  • Pollination leads to fertilization, forming zygotes that develop into seeds.
• Uses: Products like varnish and cosmetics, lumber for furniture.

Angiosperms

• Definition: Flowering plants with seeds enclosed in fruits, can be monocots or dicots.
• Structure:
  • Flowers with male (stamen) and female (pistil) reproductive organs.
  • Pollination allows fertilization, leading to seed and fruit development.
• Lifecycle: Includes double fertilization (fusion of two gametes) unique to angiosperms.
• Importance: Major source of food, fuel, fodder, and medicines, integral to ecosystems.

Alternation of Generations

• Definition: Lifecycle alternates between sporophyte and gametophyte generations.
• Observed in many plant types; dominant phase varies:
  • Haploid: Dominant in some algae.
  • Diploid: Dominant in gymnosperms and angiosperms.
  • Bryophytes: Dominant gametophyte phase; short-lived sporophyte.
  • Pteridophytes: Dominant sporophyte phase with vascular tissues.