Plant Kingdom
Complete NCERT-based revision • Chapter 3
Classification Systems
Artificial System (Linnaeus)
Based on few superficial morphological characters like habit, color, number and shape of leaves, number of stamens. Limitation: Separated closely related species and grouped unrelated ones.
Natural System (Bentham & Hooker)
Based on natural affinities using external morphology, internal anatomy, embryology, and phytochemistry.
Phylogenetic System
Based on evolutionary relationships. Includes Numerical Taxonomy (computers, codes), Cytotaxonomy (chromosome info), Chemotaxonomy (chemical constituents).
Algae
Chlorophyll-bearing, simple, thalloid, autotrophic, largely aquatic organisms
| Feature | Chlorophyceae | Phaeophyceae | Rhodophyceae |
|---|---|---|---|
| Pigments | Chl a,b | Chl a,c + Fucoxanthin | Chl a,d + r-phycoerythrin |
| Food Reserve | Starch (pyrenoids) | Mannitol/Laminarin | Floridean starch |
| Cell Wall | Cellulose + Pectose | Cellulose + Algin | Cellulose + Pectin + Polysulphate esters |
| Flagella | 2–8, equal, apical | 2, unequal, lateral | Absent |
| Habitat | FW + marine | Marine mainly | Marine (deep water) |
| Examples | Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara | Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus | Polysiphonia, Porphyra, Gracilaria, Gelidium |
NCERT: Algae morphological diversity
Algae Reproduction
- • Vegetative: Fragmentation
- • Asexual: Zoospores (flagellated, motile)
- • Sexual: Isogamy (equal gametes — Ulothrix, Spirogyra) → Anisogamy (unequal — some Chlamydomonas) → Oogamy (non-motile egg + motile sperm — Volvox, Fucus)
Economic Importance
- • Gelidium, Gracilaria: source of Agar
- • Brown algae: source of Algin
- • Red algae: source of Carrageen
- • Chlorella: space food (protein-rich unicellular green alga)
- • Laminaria, Sargassum, Porphyra: consumed as food
- • Fix ~50% of total CO₂ on Earth
Bryophytes
"Amphibians of Plant Kingdom" — dependent on water for sexual reproduction
NCERT: Bryophyte examples
Liverworts
- • Thalloid, prostrate, dorsiventral
- • Asexual: Gemmae in gemma cups (dorsal surface)
- • Ex: Marchantia
Mosses
- • Erect, radially symmetric
- • Protonema → Leafy stage
- • Ex: Funaria, Sphagnum
Sex Organs: Antheridium (♂, biflagellate antherozoids) + Archegonium (♀, flask-shaped, single egg)
Life Cycle: Dominant Gametophyte (n). Sporophyte (2n) = Foot + Seta + Capsule. Meiosis in capsule → haploid spores.
Sporophyte is attached to and nutritionally dependent on gametophyte.
Ecology: Mosses + lichens = pioneer species in succession on bare rocks. Sphagnum = peat formation.
Pteridophytes
First land plants with vascular tissue (xylem + phloem)
NCERT: Ferns and allies
Main body = Sporophyte (2n) — differentiated into true roots, stem, and leaves. Used ornamentally and medicinally.
Leaves: Microphylls (Selaginella) vs Macrophylls (Ferns — Dryopteris, Pteris, Adiantum).
Sporangia borne on sporophylls; sometimes compact into strobili/cones (Selaginella, Equisetum).
Mostly homosporous. Only Selaginella + Salvinia are heterosporous (microspores + megaspores) — precursor to seed habit.
Gametophyte (Prothallus): Free-living, small, multicellular, photosynthetic, thalloid. Needs cool, damp places. Bears antheridia + archegonia.
Classes: Psilopsida (Psilotum), Lycopsida (Selaginella, Lycopodium), Sphenopsida (Equisetum), Pteropsida (Dryopteris, Pteris, Adiantum).
Gymnosperms
Naked-seeded plants — ovules NOT enclosed by ovary wall
NCERT: Cycas, Pinus, Ginkgo
Medium to tall trees/shrubs. Sequoia = tallest tree species (giant redwood). Tap roots generally.
Cycas: Coralloid roots (N₂-fixing cyanobacteria), unbranched stem, pinnate leaves, dioecious. Megasporophylls NOT in compact cones.
Pinus: Mycorrhiza roots (fungi), branched stem, needle-like leaves, monoecious. Both cones compact. Thick cuticle + sunken stomata.
Heterosporous: Microspores → Pollen grain (reduced male gametophyte). Megaspore → Female gametophyte (with 2+ archegonia), retained in megasporangium.
Key: Gametophytes have NO free-living existence — retained within sporangia on the sporophyte. Pollen tube delivers male gametes (no water needed).
Zygote → Embryo → Ovule → Naked seed (no fruit).
Angiosperms
Flowering plants — seeds enclosed inside fruits
NCERT: Dicot and Monocot
Pollen + ovules develop in specialized flowers. Seeds enclosed in fruits. Range: Wolffia (smallest) to Eucalyptus (100+ m).
Two classes: Dicotyledons (two cotyledons) and Monocotyledons (one cotyledon).
Double fertilization (unique to angiosperms): Syngamy (sperm + egg → 2n zygote) + Triple fusion (sperm + 2 polar nuclei → 3n endosperm).
Life Cycle Patterns
Alternation of generations — critical for NEET
NCERT: Life cycle patterns
| Pattern | Dominant Phase | Examples |
|---|---|---|
| Haplontic | Gametophyte (n). Sporophyte = zygote only. | Volvox, Spirogyra, Chlamydomonas |
| Diplontic | Sporophyte (2n). Gametophyte reduced. | Fucus, all Gymno/Angiosperms |
| Haplo-diplontic | Both multicellular (alternation visible) | Ectocarpus, Polysiphonia, Kelps, all Bryophytes, all Pteridophytes |
Evolutionary Trends at a Glance
| Feature | Algae | Bryo | Pteri | Gymno | Angio |
|---|---|---|---|---|---|
| Vascular tissue | ✗ | ✗ | ✓ | ✓ | ✓ |
| Seeds | ✗ | ✗ | ✗ | ✓ naked | ✓ enclosed |
| Water for fertil. | ✓ | ✓ | ✓ | ✗ | ✗ |
| Dominant phase | n (mostly) | n | 2n | 2n | 2n |
| Archegonia | ✗ | ✓ | ✓ | ✓ | ✗ |