Plant Diversity and Morphology — NEET Biology
Diversity and morphology are pure classification recall — and NEET loves them, drawing 5–7 questions on the five kingdoms, plant groups and floral structure every year. The marks are fast if you have the categories, defining features and examples fixed in memory. This chapter organises the living world from kingdoms down to the parts of a flower, exactly as NCERT presents it, with the distinguishing features, life-cycle patterns and family characters the exam quotes almost verbatim.
1. Biological classification — the five kingdoms
Whittaker's five-kingdom system (1969) classifies by cell structure, body organisation, mode of nutrition and phylogeny:
| Kingdom | Cell | Body | Nutrition |
|---|---|---|---|
| Monera | prokaryotic | unicellular | autotroph/heterotroph |
| Protista | eukaryotic | unicellular | photosynthetic/heterotroph |
| Fungi | eukaryotic | multicellular (hyphae) | heterotroph (saprophytic/parasitic), absorptive |
| Plantae | eukaryotic | multicellular | autotroph (photosynthesis) |
| Animalia | eukaryotic | multicellular | heterotroph (holozoic) |
Later, three domains (Archaea, Bacteria, Eukarya) refined the picture. Viruses, viroids and lichens are not placed in any kingdom (viruses are non-cellular).
2. Kingdom Monera
Bacteria are the sole members — the most abundant micro-organisms. Grouped by shape: coccus, bacillus, vibrio, spirillum.
- Archaebacteria — live in extreme habitats: halophiles (salt), thermoacidophiles (hot springs), methanogens (gut of ruminants, produce methane / biogas). Special cell-wall chemistry.
- Eubacteria ("true bacteria") — include cyanobacteria (blue-green algae, photosynthetic, some fix nitrogen via heterocysts, e.g. Nostoc, Anabaena) and mycoplasma (smallest living cells, no cell wall).
- Nutrition: autotrophic (photosynthetic/chemosynthetic) or heterotrophic (saprophytic, parasitic, symbiotic).
- Reproduce mainly by binary fission; exchange genes by conjugation, transformation, transduction.
Worked example 2.1. Which bacteria produce biogas and where are they found? Methanogens (archaebacteria) — found in the gut of ruminant animals and in marshes; they produce methane (biogas) from organic matter.
3. Kingdoms Protista and Fungi
Protista (eukaryotic, mostly aquatic, unicellular): includes chrysophytes (diatoms — "diatomaceous earth"), dinoflagellates (red tides), euglenoids (Euglena — mixotrophic), slime moulds, and protozoans (Amoeba, Paramecium, Plasmodium — malaria parasite; Trypanosoma).
Fungi (eukaryotic, heterotrophic, cell wall of chitin; body of thread-like hyphae forming a mycelium):
| Class | Feature | Example |
|---|---|---|
| Phycomycetes | aseptate coenocytic hyphae; asexual zoospores | Rhizopus (bread mould), Mucor |
| Ascomycetes | sac fungi; ascospores in an ascus | Penicillium, yeast (Saccharomyces), Aspergillus |
| Basidiomycetes | club fungi; basidiospores | mushrooms (Agaricus), rusts, smuts |
| Deuteromycetes | "fungi imperfecti" (sexual stage unknown) | Alternaria, Colletotrichum |
Lichens are a symbiosis of a fungus (mycobiont) and an alga (phycobiont) — good pollution indicators. Mycorrhiza is a fungus–root association.
Worked example 3.1. Which fungal class does the antibiotic-yielding Penicillium belong to? Ascomycetes (sac fungi) — they produce ascospores in an ascus. Penicillium yields penicillin; yeast (also Ascomycetes) is used in baking and brewing.
4. Viruses, viroids and prions
- Viruses — non-cellular, obligate intracellular parasites; a nucleic acid (DNA or RNA) core in a protein capsid. Plant viruses usually have ssRNA; animal viruses ss/dsRNA or DNA; bacteriophages are usually dsDNA. Cause many diseases (mosaic, AIDS, influenza).
- Viroids — free RNA only, no protein coat (smaller than viruses; potato spindle tuber disease).
- Prions — infectious proteins (mad-cow disease, CJD).
5. The plant kingdom
The plant kingdom shows a progression from simple, water-dependent forms to complex, seed-bearing land plants, marked by alternation of generations (a haploid gametophyte alternating with a diploid sporophyte).
| Group | Features | Dominant phase | Examples |
|---|---|---|---|
| Algae | simple, autotrophic, chlorophyll; aquatic | gametophyte | Chlamydomonas, Spirogyra, Ulothrix (green); Fucus (brown); Polysiphonia (red) |
| Bryophytes | "amphibians of plant kingdom"; no vascular tissue; need water for fertilisation | gametophyte | mosses (Funaria), liverworts (Marchantia) |
| Pteridophytes | first with vascular tissue (xylem/phloem); no seeds | sporophyte | ferns (Dryopteris), Selaginella, Equisetum |
| Gymnosperms | naked seeds (no fruit); vascular; heterosporous | sporophyte | Pinus, Cycas, Ginkgo |
| Angiosperms | flowering, seeds enclosed in fruit; double fertilisation | sporophyte | all flowering plants |
Algal pigments/reserves — a NEET table: green algae (chlorophyll a,b; starch), brown algae (fucoxanthin; laminarin/mannitol), red algae (phycoerythrin; floridean starch).
Angiosperms split into dicots (two cotyledons, reticulate venation, tap root, floral parts in 4s/5s) and monocots (one cotyledon, parallel venation, fibrous root, parts in 3s).
Worked example 5.1. Why are bryophytes called the "amphibians of the plant kingdom"? They live on land but require water for fertilisation — the motile male gametes must swim to the egg — so, like amphibians, they can inhabit land but depend on water to reproduce.
6. Morphology of the root, stem and leaf
Root — non-green, positively geotropic, absorbs water/minerals. Tap root (dicots) vs fibrous root (monocots) vs adventitious. Modifications: storage (carrot, radish), respiratory (pneumatophores in mangroves), prop/stilt (banyan, maize).
Stem — bears nodes/internodes, buds; positively phototropic. Modifications: underground (potato tuber, ginger rhizome, onion bulb), tendrils, thorns (Citrus), phylloclade (Opuntia).
Leaf — the photosynthetic organ, arises at a node; venation reticulate (dicot) or parallel (monocot); simple vs compound (pinnately/palmately). Phyllotaxy = arrangement (alternate, opposite, whorled). Modifications: tendrils (pea), spines (cactus), storage.
Worked example 6.1. Pneumatophores are a modification of which organ, and what is their function? A root modification in mangrove plants growing in marshy, oxygen-poor soil; these upward-growing roots take in oxygen for respiration.
7. The flower, fruit and seed
The flower is the reproductive shoot. Its four whorls (from outside in): calyx (sepals), corolla (petals), androecium (stamens — anther + filament), gynoecium (carpels — stigma, style, ovary). Key terms:
- Symmetry: actinomorphic (radial) vs zygomorphic (bilateral).
- Ovary position: superior (hypogynous), inferior (epigynous), perigynous.
- Aestivation: the arrangement of sepals/petals in a bud (valvate, twisted, imbricate, vexillary).
- Placentation: the arrangement of ovules (marginal, axile, parietal, basal, free central).
Inflorescence = the arrangement of flowers on the axis: racemose (main axis grows, flowers laterally) vs cymose (axis ends in a flower).
Fruit develops from the ovary after fertilisation (true fruit); a false fruit involves other floral parts (apple — thalamus). Seed = fertilised ovule: seed coat, embryo (radicle, plumule, cotyledons), with/without endosperm.
Floral formula encodes structure symbolically (e.g. bracts, symmetry, whorl numbers, ovary position). Learn three families:
| Family | Floral character | Examples/uses |
|---|---|---|
| Fabaceae (pea) | zygomorphic, papilionaceous corolla, diadelphous stamens, marginal placentation | pulses, root nodules (N-fixing) |
| Solanaceae (potato) | actinomorphic, 5 fused petals, axile placentation | potato, tomato, tobacco |
| Liliaceae (lily) | actinomorphic, trimerous (3s), monocot | onion, garlic, tulip |
Worked example 7.1. In which family are the flowers zygomorphic with a papilionaceous corolla and root nodules that fix nitrogen? Fabaceae (the pea/legume family) — its papilionaceous (butterfly-shaped) flowers and nitrogen-fixing root nodules (with Rhizobium) are defining NEET facts.
8. Common traps NEET sets here
- Five kingdoms and their criteria — cell type, body, nutrition; know the defining feature of each.
- Archaebacteria types: halophiles, thermoacidophiles, methanogens (biogas).
- Fungal classes by spore type: Phycomycetes (zoospores), Ascomycetes (ascospores), Basidiomycetes (basidiospores).
- Bryophytes gametophyte-dominant; pteridophytes onward sporophyte-dominant.
- Gymnosperms naked seeds; angiosperms seeds enclosed in fruit.
- Dicot vs monocot: cotyledon number, venation, root, floral symmetry counts.
- Pneumatophores = root; phylloclade = stem; tendrils can be either.
- Racemose (indefinite axis) vs cymose (axis ends in a flower).
- Apple is a false fruit (thalamus develops).
9. Memory aids
- "Monera-Protista-Fungi-Plantae-Animalia" — the five kingdoms in order of complexity.
- "Bryophytes are amphibians" — land plants needing water to reproduce.
- "Gymno = naked seed, Angio = enclosed seed" — the seed distinction.
- "Dicot: two, reticulate, tap; Monocot: one, parallel, fibrous" — the flowering-plant split.
- "Racemose grows on, cymose ends" — inflorescence types.
- "Fabaceae fixes nitrogen" — the legume family character.
10. Exam protocol
- Fix the five kingdoms with their four defining criteria and typical examples.
- Monera: archaebacteria types, cyanobacteria (heterocysts, N-fixation), mycoplasma (smallest).
- Fungi: classify by spore type; know lichens (symbiosis) and mycorrhiza.
- Plant kingdom: order algae → bryophytes → pteridophytes → gymnosperms → angiosperms; which phase dominates; alternation of generations.
- Dicot vs monocot on cotyledon, venation, root and floral counts.
- Morphology: identify root/stem/leaf modifications and flower whorls, symmetry, placentation.
- Learn the three families (Fabaceae, Solanaceae, Liliaceae) and read floral formulae.
