Plant Kingdom

2.1 Core concepts

• Classification systems evolved in three stages — artificial systems (Linnaeus) used only gross morphology and androecium structure, gave equal weight to vegetative and sexual characters; natural systems (Bentham & Hooker) used external + internal features (anatomy, embryology, phytochemistry); phylogenetic systems are based on evolutionary relationships and are currently accepted (NCERT §3 intro, pp. 23–24).
• Numerical Taxonomy uses computers with codes assigned to all observable characters; Cytotaxonomy uses chromosome number/structure/behaviour; Chemotaxonomy uses chemical constituents of the plant (NCERT §3 intro, p. 24).
• Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic; also found on moist stones, soils, wood and in symbiosis (lichen with fungi; with animals like sloth bear) (NCERT §3.1, p. 24).
• Algal reproduction: vegetative — by fragmentation; asexual — by spores (zoospores most common, flagellated and motile); sexual — isogamous (similar gametes, flagellated as in Ulothrix or non-flagellated as in Spirogyra), anisogamous (dissimilar in size, Eudorina), oogamous (large non-motile female + small motile male, Volvox, Fucus) (NCERT §3.1, p. 24).
• Economic importance of algae: at least half of Earth's CO₂ fixation; primary producers of aquatic food cycles; Porphyra, Laminaria, Sargassum used as food; algin (brown algae) and carrageen (red algae) are commercial hydrocolloids; agar from Gelidium and Gracilaria; Chlorella — protein-rich food supplement used by space travellers (NCERT §3.1, p. 26).
• Chlorophyceae (green algae): pigments chlorophyll a and b; storage as starch in pyrenoids (protein + starch) or oil droplets; cell wall — inner cellulose + outer pectose; examples — Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara (NCERT §3.1.1, p. 26).
• Phaeophyceae (brown algae): chlorophyll a, c, carotenoids and xanthophylls; colour due to fucoxanthin; food stored as laminarin or mannitol; plant body = holdfast + stipe + frond; cellulose wall coated with algin; biflagellate pyriform zoospores with two unequal lateral flagella; examples — Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus (NCERT §3.1.2, pp. 26–27).
• Rhodophyceae (red algae): red colour due to r-phycoerythrin; mostly marine; food stored as floridean starch (similar to amylopectin/glycogen); sexual reproduction is oogamous with complex post-fertilisation development; flagella absent; examples — Polysiphonia, Porphyra, Gracilaria, Gelidium (NCERT §3.1.3, pp. 27–28).
• Bryophytes are "amphibians of the plant kingdom" — live on soil but need water for sexual reproduction; pioneer colonisers of bare rock; prevent soil erosion (NCERT §3.2, p. 29).
• Bryophyte body plan: thallus-like, attached by uni-/multicellular rhizoids; main plant body is haploid gametophyte; male sex organ = antheridium (produces biflagellate antherozoids); female = flask-shaped archegonium (single egg); zygote develops into a multicellular sporophyte attached to and dependent on the gametophyte; sporophyte cells undergo meiosis to release haploid spores (NCERT §3.2, p. 29).
• Liverworts — thalloid, dorsiventral (Marchantia); asexual reproduction by fragmentation or by gemmae in gemma cups; sporophyte = foot + seta + capsule (NCERT §3.2.1, pp. 29–30).
• Mosses — gametophyte has two stages: protonema (creeping, filamentous, develops from spore) and leafy stage (upright with spirally arranged leaves, bears sex organs); sporophyte = foot, seta, capsule (more elaborate than liverwort); Sphagnum yields peat used as fuel/packing material; examples — Funaria, Polytrichum, Sphagnum (NCERT §3.2.2, p. 30).
• Pteridophytes — first terrestrial plants with vascular tissues (xylem and phloem); sporophyte is the dominant phase and has true root, stem, leaves; leaves may be microphylls (Selaginella) or macrophylls (ferns); sporangia borne on sporophylls, which may form strobili/cones (Selaginella, Equisetum) (NCERT §3.3, p. 30).
• Pteridophyte life cycle: spores germinate to form a small free-living photosynthetic prothallus (gametophyte) bearing antheridia and archegonia; water is needed to transfer antherozoids; zygote develops into dominant sporophyte (NCERT §3.3, p. 32).
• Homosporous vs heterosporous: most pteridophytes are homosporous; Selaginella and Salvinia are heterosporous (produce macro- and microspores giving rise to female and male gametophytes respectively); female gametophyte retained on parent sporophyte — precursor to seed habit (NCERT §3.3, p. 32).
• Pteridophyte classes: Psilopsida (Psilotum); Lycopsida (Selaginella, Lycopodium); Sphenopsida (Equisetum); Pteropsida (Dryopteris, Pteris, Adiantum) (NCERT §3.3, p. 32).
• Gymnosperms (gymnos = naked, sperma = seeds) — ovules not enclosed in ovary wall; seeds remain naked after fertilisation; Sequoia among the tallest trees; mycorrhiza in Pinus; coralloid roots in Cycas associate with N₂-fixing cyanobacteria; conifer needles have reduced surface area, thick cuticle and sunken stomata (NCERT §3.4, p. 32).
• Gymnosperm reproduction: all are heterosporous; microsporangia on microsporophylls form male strobili; megasporangia (ovules) on megasporophylls form female strobili; Pinus bears both cones on same tree but Cycas has them on different trees; reduced male gametophyte = pollen grain; pollen carried by air currents; pollen tube delivers male gametes to archegonia; ovules become naked seeds; male and female gametophytes are not free-living, retained on sporophyte (NCERT §3.4, p. 33).
• Angiosperms — flowering plants; pollen and ovules develop inside flowers; seeds enclosed in fruits; range from smallest Wolffia to tall Eucalyptus (>100 m); divided into dicotyledons and monocotyledons (NCERT §3.5, p. 34).

2.2 Definitions to memorise

2.3 Diagrams / processes to remember

• Figure 3.1, p. 25 — Algae: (a) green — Volvox (with daughter colonies), Ulothrix; (b) brown — Laminaria, Fucus (note air bladder, frond, midrib), Dictyota (with stipe, frond); (c) red — Porphyra, Polysiphonia.
• Table 3.1, p. 27 — Algal classes: common name, pigments, stored food, cell wall, flagellar number/position, habitat. Highest-yield CUET table here.
• Figure 3.2, p. 28 — Bryophytes: Marchantia female (archegoniophore) and male (antheridiophore) thalli with gemma cups and rhizoids; Funaria (gametophyte with leaves + main axis + rhizoids; sporophyte with capsule + seta); Sphagnum gametophyte.
• Figure 3.3, p. 31 — Pteridophytes: Selaginella (leaves, stem, roots), Equisetum (strobilus, node, internode, branch, rhizome), fern, Salvinia.
• Figure 3.4, p. 33 — Gymnosperms: Cycas, Pinus, Ginkgo (dwarf shoot, long shoot, seeds).
• Figure 3.5, p. 34 — Angiosperms: a dicotyledon vs a monocotyledon.

2.4 Common confusions / NTA trap points

• Cyanobacteria ≠ algae. Blue-green algae are placed in Monera, NOT Plantae (NCERT §3 intro, p. 23). NTA likes to put "Nostoc / Anabaena" as a distractor under algae.
• Pigment-class pairing: r-phycoerythrin → red algae; fucoxanthin → brown algae; chlorophyll b → green algae. Mixing these is the favourite NTA trap.
• Stored food: green → starch; brown → laminarin/mannitol (NOT starch); red → floridean starch (similar to glycogen, NOT to true starch).
• Dominant phase: bryophytes — gametophyte dominant; pteridophytes/gymnosperms/angiosperms — sporophyte dominant. Saying "moss sporophyte is dominant" is a classic wrong choice.
• Cycas trivia: pinnate leaves, coralloid roots with cyanobacteria, dioecious (male and female cones on different trees). Pinus is monoecious (both cones on same tree).
• Heterosporous pteridophytes: only Selaginella and Salvinia. Equisetum, Lycopodium, Pteris, Dryopteris are homosporous.
• Sphagnum uses — peat (fuel) and packing material because of water-holding capacity; not for food.
• Isogamy/anisogamy/oogamy examples. Isogamy: Ulothrix (flagellated) and Spirogyra (non-flagellated). Anisogamy: Eudorina. Oogamy: Volvox, Fucus. NTA frequently swaps these.
• Algal cell walls. Green: inner cellulose + outer pectose. Brown: cellulose coated with algin. Red: cellulose, pectin, polysulphate esters. Distractors that swap algin and agar are common (algin is in brown algal walls; agar is extracted from red algae).
• Liverwort vs Moss asexual reproduction. Liverworts use gemmae in gemma cups; mosses develop a protonema from the germinating spore. Flipping these two is a common NTA wrong choice.
• Prothallus. The free-living photosynthetic gametophyte of pteridophytes — not of bryophytes or gymnosperms. The bryophyte gametophyte is the thallus itself; the gymnosperm gametophyte is not free-living.
• Seed habit precursor. Heterospory + retention of female gametophyte on parent sporophyte (in Selaginella) is described in NCERT (§3.3, p. 32) as a "precursor to the seed habit" — direct-quote item.
• Largest and smallest angiosperms. Smallest: Wolffia; tallest mentioned: Eucalyptus (>100 m). For gymnosperms, Sequoia is the tallest tree (NCERT §3.4, p. 32).
• Algal flagella count and insertion. Brown algal zoospores are biflagellate, pyriform, with two unequal lateral flagella. Red algae have no flagella. NTA loves this fine-grained detail.