Key Points
Key Points: Introduction of Plant Kingdom
- 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.
Key Points: Division II - Bryophyta
- 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.
Key Points: Division III - Pteridophyta
- 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.
Key Points: Phanerogams > Division I-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.
Key Points: Division II - Angiosperms
- 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.
Concepts [11]
- Introduction of Plant Kingdom
- Classification System - Artificial and Natural
- Phylogenetic Classification System
- Sub Classification of Plantae
- Concept of Algae
- Cryptogams > Division II- Bryophytes
- Cryptogams > Division III- Pteridophytes
- Phanerogams
- Phanerogams > Division I-Gymnosperms
- Phanerogams > Division II- Angiosperms
- Life Cycle Patterns in Plants
