Key Points
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.
