Kingdom Plantae: Complete One-Shot (NEET/NCERT)

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🌿 Kingdom Plantae: Complete One-Shot (NEET/NCERT)

I. Systems of Classification

Before diving into plant groups, NCERT defines how plants were classified historically.

SystemProposed ByBasis of Classification
Artificial SystemLinnaeusBased on superficial morphological characters (habit, color, number, and shape of leaves). Mainly based on androecium structure.
Natural SystemGeorge Bentham & Joseph Dalton HookerBased on natural affinities, considering ultrastructure, anatomy, embryology, and phytochemistry.
Phylogenetic System(Various)Based on evolutionary relationships. Assumes organisms in the same taxa have a common ancestor.

Modern Taxonomy Tools:

  1. Numerical Taxonomy: Uses computers; assigns numbers/codes to characters; processes all data equally.
  2. Cytotaxonomy: Based on cytological information like chromosome number, structure, and behavior.
  3. Chemotaxonomy: Uses the chemical constituents of the plant.

II. Algae (The Simple Thallophytes)

  • Structure: Chlorophyll-bearing, simple, thalloid, autotrophic, and largely aquatic (freshwater & marine).
  • Forms:
    • Colonial: Volvox
    • Filamentous: Ulothrix, Spirogyra
    • Massive Plant Bodies: Kelps (Marine forms).

Comparative Table of Algae Classes (High Yield)

FeatureChlorophyceae (Green)Phaeophyceae (Brown)Rhodophyceae (Red)
Major PigmentsChlorophyll a, bChlorophyll a, c, FucoxanthinChlorophyll a, d, r-phycoerythrin
Stored FoodStarch (Pyrenoids store protein + starch)Mannitol, Laminarin (Complex carbs)Floridean Starch (Similar to amylopectin & glycogen)
Cell WallCellulose (Inner), Pectose (Outer)Cellulose + AlginCellulose, Pectin, Polysulphate esters
Flagella2-8, equal, apical2, unequal, lateralAbsent
ExamplesChlamydomonas, Volvox, Ulothrix, Spirogyra, CharaEctocarpus, Dictyota, Laminaria, Sargassum, FucusPolysiphonia, Porphyra, Gracilaria, Gelidium

Economic Importance of Algae:

  1. CO2 Fixation: Perform 50% of total CO2 fixation on earth.
  2. Hydrocolloids (Water holding): Algin (Brown algae) and Carrageen (Red algae).
  3. Agar: From Gelidium and Gracilaria (used in microbes/ice-cream).
  4. Space Food: Chlorella (unicellular protein-rich alga).

III. Bryophytes (Amphibians of Plant Kingdom)

  • Habitat: Moist, shaded areas.
  • Key Feature: Live in soil but depend on water for sexual reproduction.
  • Plant Body: Haploid Gametophyte (Dominant). Lacks true roots/stems; has rhizoids.
  • Reproduction:
    • Male: Antheridium – Antherozoids (Biflagellate).
    • Female: Archegonium – Egg.
    • Sporophyte: Dependent on gametophyte. Divided into Foot, Seta, Capsule.

Classification: Liverworts vs. Mosses

Liverworts (Marchantia)Mosses (Funaria, Sphagnum)
Thallus is dorsiventral and appressed.Plant body has upright, slender axes with spirally arranged leaves.
Asexual reproduction by Gemmae (Green, multicellular, asexual buds).Life cycle has Protonema (creeping, green) – Leafy Stage.
Sporophyte is simple.Sporophyte is elaborate with mechanisms for spore dispersal.

Specific Note: Sphagnum (Moss) provides Peat (fuel/packing material) due to water holding capacity.

IV. Pteridophytes (First Vascular Plants)

  • Evolution: First terrestrial plants with Vascular Tissue (Xylem/Phloem).
  • Dominant Phase: Diploid Sporophyte (True root, stem, leaves).
  • Leaves: Small (Microphylls e.g., Selaginella) or Large (Macrophylls e.g., Ferns).
  • Reproduction:
    • Sporophyte bears Sporangia subtended by Sporophylls.
    • Compact structures called Strobili/Cones found in Selaginella and Equisetum.
    • Spores germinate to form Prothallus (inconspicuous, free-living, photosynthetic gametophyte).
    • Water is essential for fertilization.

Heterospory & Seed Habit (Most Important Concept)

  • Homosporous: Most pteridophytes (one type of spore).
  • Heterosporous: Produce Macro (large) and Micro (small) spores.
    • Examples: Selaginella, Salvinia.
  • Significance: Female gametophyte is retained on the parent sporophyte. Zygote develops into embryo inside the gametophyte. This is a precursor to the seed habit.

Classes:

  1. Psilopsida (Psilotum)
  2. Lycopsida (Selaginella, Lycopodium)
  3. Sphenopsida (Equisetum)
  4. Pteropsida (Dryopteris, Pteris, Adiantum)

V. Gymnosperms (Naked Seeds)

  • Ovules: Not enclosed by ovary wall; remain exposed.
  • Roots:
    • Mycorrhiza (Fungal association) – Pinus.
    • Coralloid Roots (N2-fixing cyanobacteria) – Cycas.
  • Leaves: Needle-like in conifers (reduced surface area, thick cuticle, sunken stomata).
  • Reproduction:
    • Heterosporous.
    • Male and female cones can be on same tree (Monoecious – Pinus) or different trees (Dioecious – Cycas).
    • Male gametophyte is reduced to a Pollen Grain.
    • NO free-living gametophyte.

VI. Angiosperms (Flowering Plants)

  • Key Feature: Pollen and ovules in Flowers; seeds in Fruits.
  • Classification: Dicots and Monocots.
  • Double Fertilization (Unique Event):
    1. Syngamy: Male gamete + Egg – Zygote (2n).
    2. Triple Fusion: Male gamete + Polar Nuclei – Primary Endosperm Nucleus (3n).

VII. Plant Life Cycles (Alternation of Generations)

  1. Haplontic:
    • Dominant: Gametophyte (n).
    • Sporophyte: Only Zygote (1-celled). Meiosis in Zygote.
    • Examples: Volvox, Spirogyra, Chlamydomonas.
  2. Diplontic:
    • Dominant: Sporophyte (2n).
    • Gametophyte: Single to few-celled.
    • Examples: Gymnosperms, Angiosperms, Fucus (Alga).
  3. Haplo-diplontic:
    • Intermediate condition. Both phases multicellular.
    • Examples: Bryophytes, Pteridophytes.
    • Algal Exceptions: Ectocarpus, Polysiphonia, Kelps.

Final Checklist: Common NCERT Confusions

  • Redwood Tree: Sequoia (Gymnosperm).
  • Colonial Alga: Volvox.
  • Filamentous Alga: Ulothrix, Spirogyra.
  • Alga with Diplontic Cycle: Fucus.
  • Heterosporous Pteridophytes: Selaginella, Salvinia.
  • Monoecious Gymnosperm: Pinus.
  • Dioecious Gymnosperm: Cycas.

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