Section 1: Algae — Classification and Features
Algae are non-vascular, thalloid, primarily aquatic, photosynthetic eukaryotes. Three classes are recognised in NCERT:
Chlorophyceae (Green Algae): Chlorophyll a + b; starch storage; cellulose cell walls; freshwater or shallow marine. Examples: Chlamydomonas (unicellular, biflagellate, cup-shaped chloroplast), Volvox (colonial, hollow sphere of cells), Ulothrix (unbranched filament, girdle chloroplast), Spirogyra (spiral ribbon chloroplast, conjugation), Chara (calcified, most advanced). Reproduction: isogamy, anisogamy, or oogamy depending on species.
Phaeophyceae (Brown Algae): Chlorophyll a + c + fucoxanthin (brown); laminarin storage; cellulose + algin cell walls; cold marine waters. Examples: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus. Commercial product: algin from Laminaria/Sargassum.
Rhodophyceae (Red Algae): Chlorophyll a + d + phycoerythrin (red); floridean starch storage; cellulose walls; deep marine. Examples: Polysiphonia, Porphyra, Gelidium, Gracilaria. Commercial product: agar from Gelidium and Gracilaria.
Section 2: Bryophytes — Amphibians of the Plant Kingdom
Bryophytes are the first land plants but remain water-dependent for fertilization. Key features: non-vascular, dominant gametophyte, flagellated sperm (antherozoids), sporophyte (foot + seta + capsule) dependent on gametophyte. Liverworts (Marchantia: flat thallus, gemma cups) vs mosses (Funaria: protonema → gametophore; Sphagnum: hyaline cells for water retention).
Section 3: Pteridophytes — First Vascular Plants
Pteridophytes evolved true xylem and phloem — a landmark transition. Sporophyte dominant; gametophyte = prothallus (independent, photosynthetic). Water still required for fertilization. Homosporous (Dryopteris, Equisetum, Adiantum) vs heterosporous (Selaginella, Salvinia). Heterospory = evolutionary precursor to seed habit.
Section 4: Gymnosperms — Naked Seed Plants
Gymnosperms achieved seed habit (ovules on megasporophylls) and pollen tubes (no water for fertilization). Wind-pollinated. Key examples: Pinus (needle leaves, monoecious), Cycas (dioecious, largest ovules, living fossil, motile sperm), Ginkgo (fan leaves, deciduous, living fossil), Sequoia (tallest tree).
Section 5: Angiosperms — Flowering Plants
Angiosperms: flowers, fruits enclosing seeds, double fertilization. Most successful plant group (~300,000 species). Monocots (1 cotyledon, parallel venation, fibrous root, scattered VB, trimerous) vs dicots (2 cotyledons, reticulate venation, tap root, ring VB with cambium, pentamerous). Female gametophyte = 7-celled embryo sac; endosperm = 3n (triploid).
Section 6: Alternation of Generations
Universal theme: haploid gametophyte (produces gametes by mitosis) alternates with diploid sporophyte (produces spores by meiosis). Dominant phase shifts from gametophyte (bryophytes) → sporophyte (pteridophytes → angiosperms). Gametophyte progressively reduced: visible plant (bryophytes) → small prothallus (pteridophytes) → microscopic within pollen/embryo sac (angiosperms).