Revision: Classification of Plants Science SSC (English Medium) 9th Standard Maharashtra State Board

1. Meaning- All eukaryotic, chlorophyll-containing organisms; cell wall made of cellulose; mostly autotrophic; some are insectivorous (e.g. Venus fly trap, Bladderwort) or parasitic (e.g. Cuscuta).

2. Members - Includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms.

3. Alternation of generations - Life cycle has two phases - diploid sporophyte and haploid gametophyte - which alternate with each other.

4. Plant groups at a glance:

• Algae - Simple, aquatic, no true roots/stems/leaves. e.g. Seaweed, Green algae
• Bryophytes - Non-vascular, moist environments. e.g. Mosses, Liverworts
• Pteridophytes - Vascular, no seeds, reproduce by spores. e.g. Ferns
• Gymnosperms - Naked seeds in cones, no flowers/fruits. e.g. Pine, Fir
• Angiosperms - Seeds enclosed in fruits, the most diverse group. e.g. Rose, Lily

5. Key features - Have prominent chloroplasts for photosynthesis; membrane-bound organelles; the most diverse group among all kingdoms.

• 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).

• 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.

• 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.