Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms

Algae

• Definition: Simple, chlorophyll-bearing autotrophic organisms.

• Habitat: Grow on moist rocks, stones, wood, and in freshwater.

• Forms and Sizes:

  • Unicellular: Chlamydomonas
  • Colonial: Volvox
  • Filamentous: Spirogyra
  • Massive plant bodies: Kelps

• Reproduction:

  • Vegetative: Fragmentation (each fragment develops into a thallus).
  • Asexual: Spores (e.g., zoospores).
  • Sexual: Fusion of gametes (isogamous, anisogamous, oogamous).
    • Isogamous: Fusion of similar-sized gametes (e.g. flagellated in Chlamydomonas, non-flagellated in Spirogyra).
    • Anisogamous: Fusion of dissimilar-sized gametes.
    • Oogamous: Fusion of a large non-motile female gamete and small motile male gamete.

• Functions:

  • Carbon dioxide fixation.
  • Increase dissolved oxygen in surroundings via photosynthesis.
  • Produce energy-rich compounds for aquatic organisms.
  • Commercial use: Agar (from Gelidium), ice creams, and jellies (from Gracilaria).

Classification Based on Pigments and Stored Food

• Chlorophyceae (Green Algae)

  • Members: Chlamydomonas, Volvox, Spirogyra.
  • Body forms: Unicellular, colonial, filamentous.
  • Cell wall: Outer layer of pectose, inner layer of cellulose.
  • Chloroplasts: Contain chlorophyll a and b, giving green color.
  • Reproduction: Fragmentation (vegetative), zoospores (asexual).

• Phaeophyceae (Brown Algae)

  • Members: Ectocarpus, Dictyota, Laminaria.
  • Habitat: Brackish or saltwater.
  • Body forms: Filamentous (Ectocarpus), branched (Kelp).
  • Pigments: Xanthophylls, fucoxanthin, chlorophyll a, c, and carotenoids.
  • Structure: Frond (photosynthetic organ), stipe (stalk), holdfast (attachment).
  • Reproduction: Fragmentation, flagellated spores (asexual).

• Rhodophyceae (Red Algae)

  • Members: Polysiphonia, Gracilaria, Gelidium.
  • Color: Red due to phycoerythrin.
  • Structure: Multicellular thalli.
  • Habitat: Brackish and saltwater.
  • Reproduction: Non-motile spores (asexual), motile spores (sexual).

Bryophytes

• Definition: Non-vascular, amphibians of the plant kingdom.

• Habitat: Damp, humid, and shaded localities.

• Body Structure:

  • Thallus-like, prostrate or erect.
  • Attached by rhizoids.
  • No true roots, stem, or leaves (similar structures present).
  • Main plant body: Haploid (gametophyte).
  • Gametophytes: Male (antheridia) and Female (archegonia).

• Reproduction:

  • Male (antheridia) produces motile antherozoids.
  • Female (archegonia) produces one egg.
  • Fertilization: Antherozoid fuses with egg to form zygote.
  • Zygote develops into sporophyte, which produces haploid spores via meiosis.
  • Spores germinate into gametophyte.

Types

• Liverworts

  • Habitat: Moist, shady environments.
  • Body: Dorsiventral thallus, leafy forms.
  • Reproduction: Fragmentation (asexual), gemmae in gemma cups (asexual).

• Mosses

  • Common Species: Funaria, Polytrichum, Sphagnum.
  • Life Stages: Protonema (stage with filaments), leafy stage (bears sex organs).
  • Reproduction: Fragmentation, budding (vegetative).

• Uses: Peat (fuel), rainwater percolation, prevent soil erosion, ecological pioneers, decompose rocks.

Pteridophytes

• Definition: Vascular plants; first terrestrial plants with vascular tissues.

• Habitat: Damp, cool, shady, some in sandy soil.

• Body Structure:

  • True roots, stem, and leaves.
  • Leaves (microphylls in Selaginella, macrophylls in ferns).

• Reproduction:

  • Life Cycle: Alternates between sporophyte and gametophyte.
  • Sporophyte: Produces sporangia on sporophylls or compact structures (e.g., cones in Equisetum).
  • Spores: Meiosis in sporangia -> spores -> gametophyte (prothallus).
  • Gametophyte: Bears male (antheridia) and female (archegonia) organs.
  • Fertilization: Antherozoids travel to archegonium, form zygote, develop into sporophyte.

• Types: Homosporous (same type of spores), Heterosporous (megaspores and microspores).

• Uses: Ornamentals, soil binders, medicinal.

Gymnosperms

• Definition: Seed-producing plants with naked ovules.

• Morphology:

  • Roots: Tap roots, sometimes with fungal associations (mycorrhiza in Pinus, coralloid roots in Cycas).
  • Stems: Branched or unbranched.
  • Leaves: Simple or compound, adapted to extreme climates (needle-like, thick cuticle, sunken stomata).

• Reproductive Structures:

  • Strobili (Cones): Male and female cones (same tree like Pinus or different like Cycas).
  • Microsporophylls: Bear microsporangia -> microspores -> pollen grains.
  • Megasporophylls: Bear ovules -> megaspore mother cell -> meiosis -> megaspores -> female gametophyte.
  • Fertilization: Pollen carried to ovule, pollen tube forms, zygote forms, ovule -> seed.

• Uses: Varnish, cosmetics, lumber.

Angiosperms

• Definition: Flowering plants with seeds enclosed in fruits.

• Structure:

  • Flower: Contains stamen (male) and pistil (female).
  • Stamen: Filament and anther (produce pollen grains).
  • Pistil: Stigma, style, ovary (contain ovules).

• Reproduction:

  • Pollination: Transfer of pollen to stigma.
  • Fertilization: Pollen tube forms, carries male gametes to ovule.
    • Double Fertilization: One male gamete fuses with egg (zygote), other with secondary nucleus (endosperm).

• Life Cycle: Seed germinates, embryo -> new plant.

• Uses: Food, fuel, fodder, medicines.

Alternation of Generations

• Definition: Lifecycle alternates between sporophyte (diploid) and gametophyte (haploid) stages.
• Types:
  • Haplontic: Dominant gametophyte, short-lived sporophyte (e.g., Chlamydomonas, Volvox).
  • Diplontic: Dominant sporophyte, short-lived gametophyte (e.g., gymnosperms, angiosperms).
  • Haplo-Diplontic: Both stages multicellular and free-living (e.g., bryophytes, pteridophytes).
    • Bryophytes: Dominant gametophyte, dependent sporophyte.
    • Pteridophytes: Dominant sporophyte, independent gametophyte.

Significance: Every plant lifecycle alternates between these stages with dominant phases varying across plant groups.