Quick Revision Notes: Plant Kingdom (Class 11 Biology - MP Board)

1. Introduction & Classification System

Plant Kingdom (Plantae): Includes eukaryotic, chlorophyll-containing organisms with cellulosic cell walls.
Artificial System of Classification: Proposed by Linnaeus. Based mainly on superficial morphological characters (vegetative characters and androecium structure). Limitation: Gave equal weightage to vegetative and sexual characteristics.
Natural System of Classification: Based on natural affinities among organisms (external and internal features like ultrastructure, anatomy, embryology, and phytochemistry). Given by George Bentham and Joseph Dalton Hooker.
Phylogenetic Classification Systems: Based on evolutionary relationships between various organisms. Assumes organisms belonging to the same taxa have a common ancestor. Proposed by Engler and Prantl, and widely accepted today.

Numerical Taxonomy: Based on all observable characteristics. Data is processed using computers; numbers and codes are assigned to all characters.
Cytotaxonomy: Based on cytological information like chromosome number, structure, and behaviour.
Chemotaxonomy: Uses the chemical constituents of the plant to resolve confusions.

Characteristics: Chlorophyll-bearing, simple, thalloid, autotrophic, and largely aquatic (freshwater and marine) organisms.
Reproduction:
- Vegetative: By fragmentation.
- Asexual: By different types of spores (most common is zoospores).
- Sexual: By fusion of two gametes (Isogamous, Anisogamous, or Oogamous).

Classes	Common Name	Major Pigments	Stored Food	Cell Wall	Flagellar Number & Position	Habitat
Chlorophyceae	Green Algae	Chlorophyll $a, b$	Starch	Cellulose	2-8, equal, apical	Freshwater, damp soil, marine
Phaeophyceae	Brown Algae	Chlorophyll $a, c$, Fucoxanthin	Laminarin, Mannitol	Cellulose & Algin	2, unequal, lateral	Mostly marine
Rhodophyceae	Red Algae	Chlorophyll $a, d$, Phycoerythrin	Floridean Starch	Cellulose, Pectin & Polysulphate esters	Absent	Mostly marine (warmer areas)

Key Examples:
- Chlorophyceae: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara.
- Phaeophyceae: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus.
- Rhodophyceae: Polysiphonia, Porphyra, Gracilaria, Gelidium.

The "Amphibians of the Plant Kingdom": They live in soil but are dependent on water for sexual reproduction.
Plant Body: More differentiated than algae; thallus-like, prostrate or erect, attached to the substratum by rhizoids. Lacks true roots, stem, or leaves.
Main Plant Body: Haploid ($n$) – Gametophyte.
Sex Organs: Multicellular. Male sex organ is Antheridium (produces biflagellate antherozoids); female sex organ is flask-shaped Archegonium (produces a single egg).
Sporophyte: Multicellular, not free-living, but attached to the photosynthetic gametophyte and derives nourishment from it. Zygote undergoes meiosis/mitosis to form a sporophyte consisting of foot, seta, and capsule.
Economic Importance: Food for herbaceous mammals/birds; Sphagnum (peat) provides packing material for trans-shipment of living material.
Key Examples: Liverworts (Marchantia), Mosses (Funaria, Polytrichum, Sphagnum).

First Terrestrial Plants: Possess vascular tissues (Xylem and Phloem).
Habitat: Cool, damp, shady places; some flourish well in sandy-soil conditions.
Main Plant Body: Sporophyte ($2n$) – differentiated into true root, stem, and leaves (microphylls like Selaginella or macrophylls like ferns).
Reproductive Structures: Sporophytes bear sporangia that subtend leaf-like appendages called sporophylls.
Prothallus: Spores germinate to give rise to inconspicuous, small, but multicellular, free-living, mostly photosynthetic thalloid gametophytes called prothallus (requires cool, damp places to grow).
Condition: Homosporous (all spores similar, e.g., Ferns) or Heterosporous (two kinds of spores: macro/megaspores and microspores, e.g., Selaginella, Salvinia). Heterospory is a precursor to the seed habit.
Key Examples: Psilotum, Equisetum, Dryopteris, Pteris, Adiantum.

Definition: Plants in which the ovules are not enclosed by any ovary wall and remain exposed both before and after fertilization.
Plant Body: Medium-sized trees or tall shrubs and climbers (e.g., Sequoia is one of the tallest trees).
Roots: Generally have tap roots. Roots in some have fungal association in the form of mycorrhiza (Pinus), while in some others (Cycas) small specialized roots called coralloid roots are associated with $\text{N}_2$-fixing cyanobacteria.
Reproduction: Heterosporous; produce microspores and megaspores.
- Strobili or cones (Male and Female) may be borne on the same plant (Pinus) or on different plants (Cycas).
Pollination: Wind pollination (Anemophily).
Key Examples: Cycas, Pinus, Ginkgo, Cedrus.

Definition: Flowering plants; pollen grains and ovules are developed in specialized structures called flowers. Seeds are enclosed inside fruits.
Size Range: From tiny, almost microscopic Wolffia to tall trees of Eucalyptus (over 100 meters).
Classes: Divided into two classes:
1. Dicotyledons: Two cotyledons, reticulate venation, tetramerous/pentamerous flowers.
2. Monocotyledons: Single cotyledon, parallel venation, trimerous flowers.
Double Fertilization (Unique feature):
- Syngamy: One male gamete fuses with the egg cell to form a zygote ($2n$).
- Triple Fusion: The second male gamete fuses with the diploid secondary nucleus to produce the Primary Endosperm Nucleus (PEN, $3n$), which develops into the endosperm to provide nourishment to the developing embryo.

The life cycle of plants alternates between a gametophytic generation ($n$) and a sporophytic generation ($2n$).

Haplontic Life Cycle:
- Dominant photosynthetic phase is free-living gametophyte ($n$).
- Zygote is the only sporophytic generation ($2n$); undergoes meiosis to form spores.
- Examples: Volvox, Spirogyra, Chlamydomonas.
Diplontic Life Cycle:
- Dominant, photosynthetic, independent phase is the sporophyte ($2n$).
- Gametophytic phase is represented by single to few-celled gametophyte.
- Examples: All seed-bearing plants (Gymnosperms and Angiosperms), Fucus (alga).
Haplo-diplontic Life Cycle:
- Intermediate condition. Both phases are multicellular and often free-living, though one may be dominant.
- Bryophytes: Dominant phase is photosynthetic, free-living gametophyte.
- Pteridophytes: Dominant phase is vascular sporophyte.
- Examples: Bryophytes and Pteridophytes, Kelps (Brown algae).