Plant Kingdom (Class 11 Biology)

• Introduction & Classification Systems

  • Artificial System
    • Based on vegetative characters & a few floral traits
    • Proposed by Linnaeus
    • Equal weightage to vegetative and sexual traits (flawed)
  • Natural System
    • Based on natural affinities among organisms
    • External and internal features (ultrastructure, anatomy, embryology)
    • Proposed by George Bentham and Joseph Dalton Hooker
  • Phylogenetic System
    • Based on evolutionary relationships between organisms
    • Assumes organisms belonging to the same taxa have a common ancestor
    • Numerical Taxonomy: Uses computers, all observable characteristics processed, equal weightage given to characters
    • Cytotaxonomy: Based on cytological information like chromosome number, structure, and behavior
    • Chemotaxonomy: Uses chemical constituents of the plants to resolve confusions

• Algae

  • General Characteristics
    • Chlorophyll-bearing, simple, thalloid, autotrophic
    • Mostly aquatic (freshwater and marine)
    • Form association with fungi (Lichen) and animals (sloth bear)
  • Reproduction
    • Vegetative: Fragmentation
    • Asexual: Various spores (most common is zoospores)
    • Sexual: Fusion of gametes (Isogamous, Anisogamous, or Oogamous)
  • Major Classes
    • Chlorophyceae (Green Algae)
      • Pigments: Chlorophyll $a$ and $b$
      • Stored Food: Starch
      • Cell Wall: Cellulose
      • Examples: Chlamydomonas, Spirogyra, Volvox
    • Phaeophyceae (Brown Algae)
      • Pigments: Chlorophyll $a$, $c$, and fucoxanthin
      • Stored Food: Laminarin or mannitol
      • Cell Wall: Cellulose with algin
      • Examples: Ectocarpus, Fucus, Sargassum, Laminaria
    • Rhodophyceae (Red Algae)
      • Pigments: Chlorophyll $a$, $d$, and phycoerythrin
      • Stored Food: Floridean starch
      • Cell Wall: Cellulose, pectin, and polysulphate esters
      • Examples: Polysiphonia, Porphyra, Gracilaria, Gelidium

• Bryophytes

  • General Characteristics
    • Amphibians of the plant kingdom
    • Occur in damp, humid, and shaded localities
    • Main plant body is haploid (gametophyte)
    • Lacks true roots, stem, or leaves (possesses root-like rhizoids)
  • Economic & Ecological Importance
    • Food for herbaceous animals
    • Sphagnum (peat) provides fuel and packing material for trans-shipment of living material
    • Prevents soil erosion on dense soil mats
  • Major Groups
    • Liverworts
      • Thalloid body (e.g., Marchantia)
      • Asexual reproduction by gemmae cups
    • Mosses
      • Predominant stage is protonema stage
      • Leafy stage bears sex organs (e.g., Funaria, Polytrichum)

• Pteridophytes

  • General Characteristics
    • First terrestrial plants to possess vascular tissues (xylem and phloem)
    • Main plant body is sporophyte (differentiated into true root, stem, and leaves)
    • Leaves may be small (microphylls as in Selaginella) or large (macrophylls as in ferns)
  • Reproduction & Life Cycle
    • Sporangia produce spores $\rightarrow$ germinate into inconspicuous, small, multicellular free-living thalloid gametophyte called prothallus
    • Heterospory: Production of two kinds of spores—macro (mega) and microspores (e.g., Selaginella, Salvinia) - precursor to seed habit
  • Classes
    • Psilopsida (Psilotum)
    • Lycopsida (Selaginella)
    • Sphenopsida (Equisetum)
    • Pteropsida (Dryopteris, Pteris, Adiantum)

• Gymnosperms

  • General Characteristics
    • Naked seeds (ovules are not enclosed by any ovary wall)
    • Medium-sized trees or tall trees and shrubs (e.g., Sequoia is one of the tallest)
    • Tap roots present; roots may have fungal association (mycorrhiza in Pinus) or specialized nitrogen-fixing roots (coralloid roots in Cycas)
  • Reproduction
    • Heterosporous (produces haploid microspores and megaspores)
    • Cones can be male or female on the same plant (monoecious, e.g., Pinus) or different plants (dioecious, e.g., Cycas)
    • Pollination is mainly by wind

• Angiosperms (Flowering Plants)

  • General Characteristics
    • Pollen grains and ovules are developed in specialized structures called flowers
    • Seeds are enclosed inside the fruits
    • Exceptional adaptability; ranges in size from tiny Wolffia to tall trees like Eucalyptus
  • Classes
    • Dicotyledons
      • Two cotyledons, reticulate venation, tetramenterous/pentamerous flowers
    • Monocotyledons
      • Single cotyledon, parallel venation, trimerous flowers

• Plant Life Cycles and Alternation of Generations

  • Haplontic Life Cycle
    • Dominant phase: Gametophyte (haploid)
    • Zygote is the only diploid cell (undergoes meiosis)
    • Examples: Volvox, Spirogyra, Chlamydomonas
  • Diplontic Life Cycle
    • Dominant phase: Sporophyte (diploid)
    • Gametophytic phase is represented by single to few-celled gametes
    • Examples: Gymnosperms, Angiosperms, Fucus
  • Haplo-diplontic Life Cycle
    • Intermediate condition
    • Multicellular dominant phase alternates between gametophytic and sporophytic
    • Examples: Bryophytes and Pteridophytes