Learning Objectives
- Understand the classification of the Plant Kingdom
- Learn the features of Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms
- Understand the concept of alternation of generations
- Differentiate between haplontic, diplontic, and haplo-diplontic life cycles
Key Concepts
Algae
Simple, autotrophic, thalloid plants mostly aquatic. Classified based on pigments: Chlorophyceae (green algae — chlorophyll a, b; stored food is starch; cell wall of cellulose; e.g., Chlamydomonas, Spirogyra, Ulothrix), Phaeophyceae (brown algae — chlorophyll a, c + fucoxanthin; stored food is mannitol/laminarin; e.g., Fucus, Sargassum, Laminaria), Rhodophyceae (red algae — chlorophyll a, d + phycoerythrin; stored food is floridean starch; e.g., Polysiphonia, Porphyra, Gelidium). Agar is obtained from Gelidium and Gracilaria.
Bryophytes
Called amphibians of the plant kingdom. Lack true roots, stems, and leaves. Dominant phase is gametophytic (haploid). Require water for fertilization. Divided into Liverworts (e.g., Marchantia — thalloid, gemma cups for vegetative reproduction) and Mosses (e.g., Funaria, Sphagnum). Sphagnum is used as packing material due to water-holding capacity. Mosses along with lichens are ecological succession pioneers on bare rocks.
Pteridophytes
First vascular plants (possess xylem and phloem). Dominant phase is sporophytic (diploid). Used for ornamental purposes (ferns). Classified into: Psilopsida (Psilotum), Lycopsida (Selaginella, Lycopodium), Sphenopsida (Equisetum), Pteropsida (ferns like Dryopteris, Pteris, Adiantum). Selaginella and Salvinia are heterosporous (produce microspores and megaspores).
Gymnosperms
Naked seed-bearing plants (seeds not enclosed in fruit). Sporophyte is the dominant phase. Examples: Cycas, Pinus, Ginkgo (living fossil), Sequoia (tallest tree). Male cones produce pollen (microspores), female cones produce megaspores. Pollination by wind. Fertilization does not require water.
Angiosperms
Flowering plants with seeds enclosed in fruits. Most advanced and diverse group. Divided into Dicotyledons (two cotyledons, reticulate venation, tap root) and Monocotyledons (one cotyledon, parallel venation, fibrous root). Double fertilization is unique to angiosperms.
Alternation of Generations
Plants alternate between haploid gametophytic and diploid sporophytic phases. Haplontic: Dominant gametophyte, sporophyte reduced (most algae). Diplontic: Dominant sporophyte, gametophyte reduced (all seed plants, some algae like Fucus). Haplo-diplontic: Both phases are multicellular (bryophytes — dominant gametophyte; pteridophytes — dominant sporophyte).
Summary
The Plant Kingdom is classified into Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms based on increasing complexity. Bryophytes are amphibians of the plant world. Pteridophytes are the first vascular plants. Gymnosperms bear naked seeds. Angiosperms have seeds enclosed in fruits with double fertilization. Life cycles show alternation of generations between gametophytic and sporophytic phases.
Important Terms
- Thallus: Undifferentiated plant body without true roots, stems, or leaves
- Gametophyte: Haploid, gamete-producing phase of the plant
- Sporophyte: Diploid, spore-producing phase of the plant
- Heterospory: Production of two types of spores (micro and mega)
- Double fertilization: Fusion of one sperm with egg and another with polar nuclei (unique to angiosperms)
- Agar: Gelatinous substance from red algae used in culture media
- Archegonium: Female sex organ in bryophytes and pteridophytes
- Antheridium: Male sex organ producing antherozoids (sperm)
Quick Revision
- Algae: Chlorophyceae (green), Phaeophyceae (brown), Rhodophyceae (red)
- Bryophytes = amphibians of plant kingdom; dominant gametophyte
- Pteridophytes = first vascular plants; dominant sporophyte
- Gymnosperms = naked seeds; Cycas, Pinus, Ginkgo
- Angiosperms = enclosed seeds; double fertilization
- Heterospory seen in Selaginella and Salvinia
- Agar from Gelidium/Gracilaria (red algae)
- Sphagnum used for packing; holds water