Revision: Class 11 >> Plant Kingdom NEET (UG) Plant Kingdom

Thallus refers to a plant body that is not differentiated into roots, stems, and leaves. Example: Algae.

• Plant cells have a cell wall primarily made of cellulose, providing rigidity and structural support.
• Most plants are autotrophic; they synthesise food (glucose) through photosynthesis using sunlight, water and CO₂; they release oxygen as a byproduct.
• The life cycle involves two phases - the haploid gametophyte and the diploid sporophyte - alternating with each other.
• The plant kingdom ranges from tiny mosses to towering trees; it shows a wide spectrum of adaptations and life cycles.

• Artificial system - Given by Carolus Linnaeus; based on vegetative characters and androecium (flower) structure; simplest but not natural.
• Natural system - Given by George Bentham and J.D. Hooker; based on natural affinities; included both external and internal features.
• Phylogenetic system - Given by Hutchinson; based on evolutionary relationships among organisms; the most advanced system.
• The plant kingdom is divided into 2 groups: Cryptogamae (no seeds), which includes Thallophyta, Bryophyta and Pteridophyta; and Phanerogamae (with seeds), which includes Gymnospermae and Angiospermae (Dicots + Monocots).
• Algae are further divided into Chlorophyceae (green), Phaeophyceae (brown) and Rhodophyceae (red algae).

• Artificial system - Based on superficial characteristics like habits, numbers, colours and leaf shapes; leads to grouping of many organisms together.
• Natural (Phenetic) system - Based on natural affinities; considers structure, anatomy, embryology and phytochemistry; more reliable than artificial system.
• Phylogenetic system - Based on evolutionary and genetic relationships; uses fossil records, biochemical, anatomical, morphological and physiological data.
• Numerical taxonomy - Carried out using computers; based on all observable characteristics; data assigned with numbers, codes and symbols; advantage - each character gets equal importance.
• Cytotaxonomy - Based on cytological information like chromosome number, structure and behaviour of cells; considers cell structure and functions.
• Chemotaxonomy - Based on chemical constituents (plant chemicals) for classification; it uses biochemical differences among organisms.

• Artificial system - Based on superficial characteristics like habits, numbers, colours and leaf shapes; leads to grouping of many organisms together.
• Natural (Phenetic) system - Based on natural affinities; considers structure, anatomy, embryology and phytochemistry; more reliable than artificial system.
• Phylogenetic system - Based on evolutionary and genetic relationships; uses fossil records, biochemical, anatomical, morphological and physiological data.
• Numerical taxonomy - Carried out using computers; based on all observable characteristics; data assigned with numbers, codes and symbols; advantage - each character gets equal importance.
• Cytotaxonomy - Based on cytological information like chromosome number, structure and behaviour of cells; considers cell structure and functions.
• Chemotaxonomy - Based on chemical constituents (plant chemicals) for classification; it uses biochemical differences among organisms.

• Cryptogamae are non-seed plants that reproduce by spores.
• They usually lack well-developed roots, stems, and leaves.
• In thallophyta and bryophyta, the gametophyte is dominant.
• In pteridophyta, the sporophyte is dominant.
• They mostly grow in moist habitats, as water is needed for reproduction.

• Thallophyta have a simple thallus body and lack true roots, stems, and leaves.
• They do not have vascular tissues, so transport of water and nutrients is simple.
• They are mostly found in moist environments like freshwater, marine, and damp areas.
• Reproduction occurs by asexual methods such as fragmentation and spore formation.
• They show wide diversity, ranging from microscopic forms to large multicellular seaweeds, and may form symbiotic associations (e.g., lichens).

• Algae are simple, chlorophyll-containing, autotrophic organisms, mostly found in aquatic habitats.
• They have a thallus body without true roots, stems, and leaves.
• Algae show different forms, such as unicellular (Chlamydomonas), colonial (Volvox), and filamentous (Spirogyra).
• Reproduction occurs by vegetative, asexual, and sexual methods, including fragmentation and spore formation.
• Algae play an important role in CO₂ fixation and oxygen production, supporting aquatic ecosystems.
• They have economic importance, providing food, agar, algin, carrageenan, and protein-rich supplements like Spirulina.

• Bryophytes are called amphibians of the plant kingdom as they live on land but need water for reproduction.
• They are found in damp, humid, and shaded places and lack true roots, stems, and leaves.
• The plant body is thallus-like and attached to the substratum by rhizoids.
• The gametophyte is the dominant phase, which produces male (antheridia) and female (archegonia) gametes.
• Fertilisation requires water, forming a zygote that develops into a sporophyte (foot, seta, capsule).
• Reproduction occurs by vegetative (fragmentation), asexual (gemmae), and sexual methods.
• Economic importance: prevents soil erosion, acts as a pioneer species, provides peat (fuel), and has medicinal uses.

• Pteridophytes are vascular plants with true roots, stems, and leaves; the sporophyte is the dominant phase.
• They are the first terrestrial plants with vascular tissues (xylem and phloem).
• Leaves may be microphylls (small), as in Selaginella, or macrophylls (large), as in ferns.
• Sporangia produce spores and are present on sporophylls, often forming cones (strobili).
• Spores germinate into a haploid gametophyte (prothallus), which is small, independent, and photosynthetic.
• Fertilisation requires water, and the zygote develops into a new sporophyte.
• Some pteridophytes show heterospory (microspores and megaspores), which is an important step towards a seed habit.

• Phanerogamae are seed-producing plants, also called spermatophytes.
• They have well-developed roots, stems, and leaves (vascular plants).
• They reproduce by seeds, which are enclosed in fruits (angiosperms) or naked (gymnosperms).
• They are widely distributed and can adapt to different environments like deserts and forests.

• Spermatophytes are seed-producing plants; seeds contain an embryo + a food reserve; this is important for dispersal and survival.
• Possess vascular tissue (xylem and phloem) for the transport of water, nutrients and sugars.
• Sporophyte generation is dominant; the gametophyte is reduced and dependent on the sporophyte.
• Reproductive structures - flowers in angiosperms and cones in gymnosperms.

• Naked seeds - Gymnosperms have ovules not enclosed by the ovary wall; seeds remain exposed before and after fertilisation.
• Vegetative features - Stem branched (Pinus) or unbranched (Cycas); leaves are needle-like with thick cuticle and sunken stomata to reduce water loss; roots are tap roots.
• Special roots - Pinus has mycorrhiza (fungal association); Cycas has coralloid roots with N₂-fixing cyanobacteria.
• Reproduction - Reproductive structures are strobili (cones); plants are heterosporous - male strobilus has microsporophylls (produce pollen); female strobilus has megasporophylls (bear ovules); pollination is by air (wind).
• Fertilisation - Pollen tube carries male gametes to archegonium → fuses with egg → zygote → embryo; ovule develops into seed; life cycle is diplontic (sporophyte dominant).
• 4 groups - Cycads (Cycas), Conifers (Pinus, Cedrus), Ginkgoales (Ginkgo biloba), Gnetales (Ephedra, Gnetum).
• Economic importance - Ephedrine (from Ephedra) for respiration; Taxol (from Taxus) for cancer; sago from Cycas; timber, resins, turpentine and paper pulp from conifers.

• Angiosperms are flowering plants with seeds enclosed in fruits.
• They show great variation in size, from small (Wolffia) to large trees (Eucalyptus).
• Classified into monocots and dicots.
• Double fertilisation occurs, forming a zygote and a triploid endosperm.
• After fertilisation, the ovary becomes a fruit, and the ovule becomes a seed.
• Life cycle is diplontic with a dominant sporophyte and a reduced gametophyte.