Notes Class 11 Chapter 3 Biology Maharashtra Board

Kingdom Plantae

1. Introduction to Kingdom Plantae

Kingdom Plantae includes all eukaryotic, multicellular, photosynthetic organisms, commonly known as plants. Plants are producers on land because they perform photosynthesis, converting solar energy into chemical energy, producing food, and releasing oxygen, forming the base of terrestrial food chains.

Classification Basis

Kingdom Plantae is classified based on:

• Presence or absence of seeds: Phanerogamae (seed-producing) vs. Cryptogamae (spore-producing).
• Vascular tissues: Presence or absence of xylem and phloem.
• Plant body differentiation: Undifferentiated (thallus) or differentiated into roots, stems, and leaves.

Major Divisions

• Cryptogamae: Non-seed-producing plants with hidden reproductive organs (e.g., algae, bryophytes, pteridophytes).
• Phanerogamae: Seed-producing plants with visible reproductive structures (e.g., gymnosperms, angiosperms).

Chart: Classification of Kingdom Plantae

2. Cryptogamae: Salient Features

A. Division: Thallophyta (Algae)

• Habitat: Mostly aquatic (marine or freshwater), some epiphytic or epizoic (non-parasitic on living organisms). Examples: Chlorella (symbiotic), Sargassum (marine).
• Plant Body: Thalloid, undifferentiated into roots, stems, or leaves. Can be:
  • Unicellular (e.g., Chlorella, Chlamydomonas).
  • Multicellular, unbranched filamentous (e.g., Spirogyra).
  • Branched filamentous (e.g., Chara).
  • Macroscopic (e.g., Sargassum, >60 meters).
• Cell Wall: Contains polysaccharides (cellulose/glucose) or proteins.
• Reserve Food: Starch or its derivatives.
• Reproduction:
  • Vegetative: Fragmentation, cell division.
  • Asexual: Spores (zoospores, aplanospores).
  • Sexual: Gametes; exhibits alternation of generations (haploid dominant, diploid reduced).
• Pigments: Chlorophyll, xanthophylls, phycobilins classify algae into subgroups.

Subgroups of Algae

1. Chlorophyceae (Green Algae):
   • Habitat: Mostly freshwater, some brackish or marine.
   • Plant Body: Unicellular (Chlamydomonas), colonial (Volvox), or filamentous (Spirogyra).
   • Cell Wall: Cellulose.
   • Pigments: Chlorophyll a and b.
   • Chloroplast Shapes: Discoid, plate-like, reticulate, cup-shaped, ribbon-shaped, or spiral.
   • Reserve Food: True starch.
   • Features: Pyrenoids (starch storage) in chloroplasts. Chlorella is protein-rich, used as food (even by space travelers).
   • Examples: Chlamydomonas, Spirogyra, Chara, Volvox, Ulothrix.
2. Phaeophyceae (Brown Algae):
   • Habitat: Mostly marine, rarely freshwater.
   • Plant Body: Simple branched (Ectocarpus), profusely branched (Petalonia), or differentiated into holdfast, stipe (stalk), and frond (leaf-like).
   • Cell Wall: Cellulose, fucans, algin.
   • Pigments: Chlorophyll a, c, fucoxanthin.
   • Reserve Food: Mannitol, laminarin, starch.
   • Economic Importance: Used as food (Laminaria), hydrocolloids (Ectocarpus).
   • Examples: Laminaria, Sargassum, Fucus, Ectocarpus.
3. Rhodophyceae (Red Algae):
   • Habitat: Marine, freshwater, brackish, or deep sea.
   • Plant Body: Thalloid.
   • Cell Wall: Cellulose, pectin, carbohydrates.
   • Pigments: Chlorophyll a, d, phycoerythrin.
   • Reserve Food: Floridean starch.
   • Economic Importance: Agar-agar (used in tissue culture) from Gelidium, Gracillaria.
   • Examples: Chondrus, Batrachospermum, Porphyra, Gelidium, Polysiphonia.

Economic and Environmental Importance of Algae

• Economic: Food (Chlorella, Laminaria), agar-agar, hydrocolloids, biofuels.
• Environmental: Oxygen production, primary producers in aquatic ecosystems, nitrogen fixation (Nostoc).

Note: Brown algae like kelps (Sargassum) can grow up to 100 meters. The Sargasso Sea is named after Sargassum.

B. Division: Bryophyta

• Habitat: Terrestrial, moist, shady places. Require water for fertilization, hence called amphibious plants.
• Plant Body: Thalloid or leafy, represents gametophyte (haploid, dominant). Sporophyte (diploid) is short-lived, dependent on gametophyte.
• Rhizoids: Root-like structures for absorption and anchorage; unicellular in liverworts, multicellular in mosses.
• Life Cycle: Alternation of generations with dominant gametophyte and reduced sporophyte.
• Groups:
  1. Liverworts (Hepaticeae):
     • Primitive, with flat, dorsiventral thallus.
     • Unicellular rhizoids.
     • Examples: Riccia, Marchantia.
     • Hornworts (Anthocerotae): Thallus with horny sporophytes. Example: Anthoceros.
  2. Mosses (Musci):
     • Advanced, with erect plant body.
     • Two gametophytic stages:
       • Protonema: Prostrate, green, filamentous, bears buds for vegetative propagation.
       • Leafy Stage: Erect, with stem-like (cauloid), leaf-like (phylloid), and multicellular rhizoids. Bears sex organs.
     • Examples: Funaria, Polytrichum, Sphagnum.
• Economic Importance:
  • Sphagnum (peat moss): Fuel, packing material due to water-holding capacity.
  • Soil formation: Decompose rocks, making soil suitable for higher plants.
  • Soil binders: Prevent erosion.
  • Food for herbivores.

C. Division: Pteridophyta

• Evolutionary Significance: First vascular, true land plants with xylem (tracheids) and phloem (sieve cells). Called vascular cryptogams due to spore-based reproduction.
• Habitat: Moist, shady places; some aquatic (Azolla, Marsilea), xerophytic (Equisetum), or epiphytic (Lycopodium).
• Plant Body: Sporophyte (diploid, dominant, autotrophic) differentiated into roots, stems, leaves. Gametophyte is haploid, short-lived, autotrophic.
• Leaves: Pinnate, either microphylls (small, e.g., Selaginella) or macrophylls (large, e.g., Nephrolepis).
• Vascular System: Xylem (tracheids only), phloem (sieve cells only). No secondary growth due to absence of cambium.
• Life Cycle: Heteromorphic alternation of generations (diploid sporophyte dominant).
• Classification:
  • Psilopsida: Psilotum.
  • Lycopsida: Selaginella, Lycopodium.
  • Sphenopsida: Equisetum.
  • Pteropsida: Dryopteris, Pteris, Adiantum.
• Economic Importance:
  • Medicinal uses.
  • Soil binders.
  • Ornamental plants (ferns).
• Examples: Nephrolepis (fern), Equisetum (horsetail).

3. Phanerogamae: Salient Features

A. Gymnospermae

• Definition: Primitive flowering plants with naked seeds (not enclosed in fruit).
• Distribution: ~70 genera, 1000 species globally; 16 genera, 53 species in India.
• Plant Body: Sporophyte (diploid, dominant), differentiated into roots, stems, leaves. Evergreen shrubs or woody trees.
• Roots: Tap root system. Some form symbiotic associations:
  • Coralloid roots (Cycas): With blue-green algae.
  • Mycorrhizae (Pinus): With fungi.
• Stem: Erect, aerial, solid, cylindrical. Unbranched (Cycas) or branched (conifers). Secondary growth due to cambium.
• Leaves: Dimorphic:
  • Foliage leaves: Green, needle-like, or pinnately compound.
  • Scale leaves: Small, membranous, brown.
• Reproduction: Heterosporous with microsporophylls (male cones) and megasporophylls (female cones).
• Economic Importance:
  • Ornamental (Cycas).
  • Timber, turpentine, resin (Pinus).
• Examples: Cycas, Pinus, Ginkgo biloba (living fossil), Sequoia sempervirens (tallest, ~366 feet), Zamia pygmaea (smallest, ~25 cm).

B. Angiospermae

• Definition: Most advanced flowering plants with enclosed seeds (within fruit/ovary).
• Plant Body: Sporophyte (diploid, dominant, autotrophic). Gametophytes (male/female) are haploid, reduced, parasitic within sporophyte.
• Reproduction: Heterosporous:
  • Microspores (pollen): Formed in anthers (microsporophylls/stamens).
  • Megaspores: Formed in ovules (megasporophylls/carpels).
• Flower Structure: Includes essential whorls (androecium, gynoecium) and accessory whorls (calyx, corolla).
• Unique Feature: Double fertilization (one sperm forms zygote, another forms endosperm).
• Classes:
  1. Dicotyledonae:
     • Embryo: Two cotyledons.
     • Roots: Tap root system.
     • Stem: Branched.
     • Leaves: Reticulate venation.
     • Flowers: Tetra- or pentamerous.
     • Vascular Bundles: Conjoint, collateral, open (cambium present).
     • Secondary Growth: Common.
     • Examples: Helianthus annuus (sunflower), Hibiscus rosa-sinensis (China rose).
  2. Monocotyledonae:
     • Embryo: Single cotyledon.
     • Roots: Adventitious.
     • Stem: Rarely branched.
     • Leaves: Parallel venation, sheathing leaf base.
     • Flowers: Trimerous.
     • Vascular Bundles: Conjoint, collateral, closed (no cambium).
     • Secondary Growth: Absent (except few cases).
     • Examples: Zea mays (maize), Sorghum vulgare (jowar).
• Size Variation: Wolffia (smallest, 1 mm) to Eucalyptus (>100 meters).
• Economic Importance: Food, timber, medicines, fibers, ornamental plants.

4. Plant Life Cycle and Alternation of Generations

• Definition: Plants exhibit two phases in their life cycle:
  • Sporophyte: Diploid (2n), produces haploid spores via meiosis.
  • Gametophyte: Haploid (n), produces gametes via mitosis.
• Alternation of Generations: Sporophyte and gametophyte alternate. The zygote (2n) forms the sporophyte, which produces spores (n) that develop into the gametophyte. Gametes fuse to form the zygote, restarting the cycle.
• Types of Life Cycles:
  1. Haplontic: Haploid phase dominant (e.g., some algae, fungi). Mitosis in haploid cells; zygote (diploid) undergoes meiosis.
  2. Diplontic: Diploid phase dominant (e.g., animals). Mitosis in diploid cells; gametes formed via meiosis.
  3. Haplo-diplontic: Both haploid and diploid phases multicellular (e.g., land plants, some algae). Seen in Bryophytes (gametophyte dominant) and Pteridophytes (sporophyte dominant).
• In Gymnosperms/Angiosperms: Gametophyte is reduced, parasitic within sporophyte.

5. Key Differences

Cryptogamae vs. Phanerogamae

Thallophyta vs. Bryophyta

Bryophyta vs. Pteridophyta

Gymnospermae vs. Angiospermae

Dicotyledonae vs. Monocotyledonae