Chapter 2: Plant Kingdom

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Plant Kingdom

Classification and Characteristics

• Multicellular, photosynthetic organisms; major producers in biosphere.

• Habitats: aquatic, terrestrial, and others.

• Classification systems evolved: artificial (Linnaeus), natural (Bentham & Hooker), phylogenetic (evolution-based).

• Artificial systems: based on few characters, separated related species, gave equal weight to vegetative and sexual traits.

• Natural systems: based on natural affinities, consider external and internal features (anatomy, embryology, phytochemistry).

• Phylogenetic systems: group organisms by common ancestry.

• Modern methods: numerical taxonomy (computer-based, all characters weighted equally), cytotaxonomy (chromosome data), chemotaxonomy (chemical constituents).

• Plant kingdom divided into Cryptogamae (non-seed plants) and Phanerogamae (seed plants).

Memory Aids

• Cryptogamae = \"hidden seeds\" (no seeds).

• Phanerogamae = \"visible seeds\" (seed plants).

• Phylogenetic = \"family tree\" classification.

Quick Checkpoints

• Difference between artificial and natural classification?

• What is basis of phylogenetic classification?

• Examples of modern taxonomy methods?

Algae

General Characteristics

• Simple, chlorophyll-containing, autotrophic, mostly aquatic organisms.

• Habitats: freshwater, marine, moist terrestrial, symbiotic (e.g., lichens with fungi, on animals).

• Unusual habitats include halophytic (saline), epiphytic (on plants), epizoic (on animals), endozoic (inside animals), parasitic, thermophytic (hot springs).

• Forms vary: unicellular (Chlamydomonas), colonial (Volvox), filamentous (Ulothrix), large kelps (brown algae).

• Vegetative body called thallus; cell wall has inner cellulose and outer pectin layers.

• Photosynthetic pigments: chlorophyll a (all), chlorophyll b, c, d; carotenoids (carotenes-orange, xanthophylls-yellow); phycobilins (phycocyanins, phycoerythrins).

• Food reserves: starch, laminarin, mannitol, floridean starch.

• Reproduction: vegetative (fragmentation), asexual (zoospores - flagellated, motile), sexual (isogamy, anisogamy, oogamy).

Memory Aids

• Thallus = simple plant body without true roots, stems, leaves.

• Isogamy = equal gametes; Anisogamy = unequal gametes; Oogamy = large non-motile egg + small motile sperm.

• Kelps = large brown algae, \"trees of the sea\".

Quick Checkpoints

• What pigments are common in all algae?

• Define thallus and its cell wall composition.

• Types of sexual reproduction in algae?

Classification of Algae

Major Classes

• Based on phylogeny and affinities, algae classified by Dr. F.E. Fritsch.

• Whittaker's system divides algae into three main classes: Chlorophyceae (green), Phaeophyceae (brown), Rhodophyceae (red).

Memory Aids

• Chlorophyceae = green algae; Phaeophyceae = brown algae; Rhodophyceae = red algae.

Quick Checkpoints

• Who classified algae based on phylogeny?

• What are the three main classes of algae?

Chlorophyceae

Characteristics

• Commonly called green algae; plant body unicellular, colonial, or filamentous.

• Photosynthetic pigments: chlorophyll a and b in definite chloroplasts (reticulate, cup-shaped, spiral, or ribbon-shaped).

• Pyrenoids in chloroplasts store protein and starch; some store oil droplets.

• Cell wall: inner cellulose layer, outer pectose layer.

• Reproduction: vegetative by fragmentation/spores; asexual by flagellated zoospores; sexual by isogamy, anisogamy, or oogamy.

Memory Aids

• Green algae = chlorophyll a + b, pyrenoids present.

• Reproduction types: all three sexual modes possible.

Quick Checkpoints

• What pigments are present in Chlorophyceae?

• Describe the cell wall layers.

• Modes of reproduction in Chlorophyceae?

Phaeophyceae

Characteristics

• Commonly called brown algae; mostly marine.

• Range from simple filamentous (Ectocarpus) to large kelps (up to 100 m).

• Pigments: chlorophyll a, carotenoids, xanthophylls (fucoxanthin gives brown color).

• Plant body parts: holdfast (attachment), stipe (stalk), frond (leaf-like).

• Reproduction: vegetative by fragmentation; asexual by biflagellate zoospores (pear-shaped, two unequal flagella); sexual by isogamy, anisogamy, or oogamy.

• Gametes are pear-shaped with two lateral flagella; fusion in water or oogonium.

Memory Aids

• Brown algae = fucoxanthin pigment.

• Body parts: holdfast, stipe, frond.

• Zoospores have two unequal flagella.

Quick Checkpoints

• What pigment causes brown color in Phaeophyceae?

• Name the three main body parts of brown algae.

• Describe zoospore flagella in brown algae.

Rhodophyceae

Characteristics

• Commonly called red algae due to red pigment phycoerythrin.

• Found near surface and at great ocean depths (low light).

• Food stored as floridean starch (similar to glycogen and amylopectin).

• Mostly multicellular with complex body organization.

• Reproduction: vegetative by fragmentation; asexual by non-motile spores; sexual reproduction oogamous with complex post-fertilization development.

Memory Aids

• Red algae = phycoerythrin pigment.

• Floridean starch as food reserve.

• Sexual reproduction is oogamous with non-motile gametes.

Quick Checkpoints

• What pigment gives red algae their color?

• What is the food reserve in Rhodophyceae?

• Describe sexual reproduction in red algae.

Economic Importance of Algae

Uses

• Food: Edible algae include Porphyra, Laminaria, Sargassum; Chlorella is protein-rich supplement.

• Photosynthesis: Algae contribute ~50% of Earth's photosynthesis; vital for aquatic respiration.

• Phycocolloids:

  • Alginic acid (from brown algae) used in emulsions, flameproof plastics, security glass.

  • Agar-agar (from red algae) used as solidifying agent in culture media.

  • Carrageenan (from red algae) used in pharmaceuticals, cleaning, textile, leather, brewing.

• Medicines: Antibiotics from brown (Laminaria, Ascophyllum) and green algae (Chlorella, Caulerpa); vermifuge from Durvillea; worm infection cure from red algae Corallina.

• Sewage disposal: Green algae (Chlamydomonas, Chlorella, Scenedesmus) aid aerobic sewage treatment.

Memory Aids

• Alginic acid = brown algae; Agar = red algae.

• Algae = major oxygen producers in water.

• Medicinal algae: antibiotics and vermifuge sources.

Quick Checkpoints

• Name algae used as food supplements.

• What phycocolloids are derived from algae?

• Role of algae in sewage treatment?

Additional Facts

Key Points

• Study of algae is called phycology.

• Algae are non-embryophytes: no embryo, unicellular non-jacketed sex organs.

• Batrachospermum: freshwater filamentous red alga, called frog spawn alga.

• Laminaria species known as Devil's Apron.

• Macrocystis pyrifera is the largest alga.

• Brown algal cells may have fucosan vesicles containing phenolic fucosan.

• Spirogyra called pond silk due to mucilage shining like silk.

Memory Aids

• Phycology = algae study.

• Non-embryophytes = no embryo formation.

• Largest alga = Macrocystis pyrifera.

Quick Checkpoints

• What is phycology?

• Define non-embryophytes.

• Which is the largest alga?

General Characteristics

Overview

• Bryophytes are called amphibians of the plant kingdom; live on soil but need water for sexual reproduction.

• Found in damp, humid, shaded areas; important in succession on bare rocks/soil.

• Plant body is thallus-like, prostrate or erect, attached by unicellular/multicellular rhizoids.

• Lack true roots, stems, or leaves but may have similar structures.

• Main plant body is haploid gametophyte producing gametes.

• Male sex organ: antheridium producing biflagellate antherozoids.

• Female sex organ: flask-shaped archegonium producing a single egg.

• Antherozoids swim in water to fertilize egg forming zygote.

• Zygote forms sporophyte attached to gametophyte; sporophyte produces haploid spores by meiosis.

• Spores germinate into gametophytes, completing life cycle.

Memory Aids

• \"Amphibians\" = need water for reproduction.

• Gametophyte is dominant and haploid.

• Antheridium = male; Archegonium = female.

• Sporophyte depends on gametophyte.

Quick Checkpoints

• Why are bryophytes called amphibians of plant kingdom?

• What is the dominant phase in bryophytes?

• Structure and function of antheridium and archegonium?

• Relationship between sporophyte and gametophyte?

Types of Bryophytes

Liverworts

• Also called Hepaticopsida or Hepaticae.

• Grow in moist, shady habitats: banks, marshy ground, damp soil, tree bark.

• Plant body is thalloid (e.g., Marchantia), dorsiventral, closely attached to substratum.

• Leafy liverworts have tiny leaf-like appendages in two rows on stem-like structures.

• Asexual reproduction by fragmentation or gemmae (multicellular buds) in gemma cups.

• Sexual reproduction: male and female sex organs on same or different thalli.

• Sporophyte has foot, seta, and capsule; spores formed after meiosis germinate into gametophytes.

• Examples: Riccia, Marchantia.

Mosses

• Dominant gametophyte stage with two phases: protonema and leafy stage.

• Protonema: creeping, green, branched, filamentous stage from spore.

• Leafy stage develops from lateral buds on secondary protonema; upright axes with spirally arranged leaves.

• Attached to soil by multicellular, branched rhizoids.

• Vegetative reproduction by fragmentation and budding in secondary protonema.

• Sex organs (antheridia and archegonia) at apex of leafy shoots.

• After fertilization, zygote forms sporophyte with foot, seta, capsule containing spores.

• Examples: Funaria, Polytrichum, Sphagnum.

Memory Aids

• Liverworts = Hepaticae, thalloid, gemma cups for asexual reproduction.

• Mosses = protonema + leafy gametophyte, sporophyte with capsule.

• Funaria and Sphagnum are common moss examples.

Quick Checkpoints

• What are gemmae and their role in liverworts?

• Describe protonema and leafy stages in mosses.

• Structure of sporophyte in bryophytes?

• Examples of liverworts and mosses?

Economic Importance of Bryophytes

Key Roles

• Prevention of soil erosion: Mosses form dense mats reducing soil loss by water and rain impact.

• Soil formation: Bryophytes aid ecological succession on rocks; e.g., Sphagnum fills ponds with soil.

• Water retention: Sphagnum absorbs 18-26 times its weight in water; used in gardening and plant transport.

• Peat formation: Dead mosses in acidic marshes form peat, used as manure, fuel, and soil conditioner.

• Ecological importance: First colonizers of rocks along with lichens.

Memory Aids

• Sphagnum = water retention and peat formation.

• Moss mats = soil erosion control.

• Peat = fuel and manure.

Quick Checkpoints

• How do bryophytes prevent soil erosion?

• Role of Sphagnum in water retention and peat formation?

• Ecological significance of bryophytes in succession?

Additional Facts

Notable Points

• Study of bryophytes is called Bryology.

• Tallest bryophytes reach up to 70 cm, e.g., Dawsonia.

• Polytrichum is known as hair cap moss.

• Sphagnum is also called famine food.

Memory Aids

• Bryology = study of bryophytes.

• Dawsonia = tallest bryophyte.

• Polytrichum = hair cap moss.

• Sphagnum = famine food.

Quick Checkpoints

• What is Bryology?

• Name the tallest bryophyte.

• Common names of Polytrichum and Sphagnum.

Pteridophytes

General Characteristics

Features

• Pteridophytes include horsetails and ferns; first terrestrial plants with vascular tissues (xylem, phloem).

• Found in cool, damp, shady places; some grow in sandy soils.

• Main plant body is sporophyte with true roots, stems, and leaves (microphylls or macrophylls).

• Sporophytes bear sporangia on leaf-like structures called sporophylls; may form strobili or cones (e.g., Selaginella, Equisetum).

• Spores produced by meiosis germinate into free-living, photosynthetic gametophytes called prothallus.

• Gametophytes bear male (antheridia) and female (archegonia) sex organs; require water for fertilization.

• Fertilization forms zygote, which develops into dominant sporophyte.

• Most pteridophytes are homosporous; some (e.g., Selaginella, Salvinia) are heterosporous producing microspores and megaspores.

• Heterosporous gametophytes develop on parent sporophyte; embryo development within female gametophyte is precursor to seed habit.

Memory Aids

• Pteridophytes = first vascular plants without seeds.

• Sporophyte dominant; gametophyte = prothallus.

• Homosporous = one spore type; heterosporous = two spore types.

Quick Checkpoints

• What is the dominant phase in pteridophytes?

• Define sporophyll and strobili.

• Difference between homosporous and heterosporous plants.

• Role of water in pteridophyte reproduction.

Classification of Pteridophytes

Classes and Features

• Psilopsida: Oldest vascular plants; no roots, have rhizoids; all extinct; e.g., Psilotum.

• Lycopsida: Club/spike mosses; have roots, stems, leaves; homosporous or heterosporous; e.g., Lycopodium, Selaginella.

• Sphenopsida: Stems with ridges/grooves; small leaves in whorls; always homosporous; spores in stalked sporangia; e.g., Equisetum.

• Pteropsida: Largest, most advanced; mostly no aerial stem except tree ferns; spores in sori on leaves; homosporous or heterosporous; e.g., Dryopteris, Marsilea.

Memory Aids

• PLSP = Psilopsida, Lycopsida, Sphenopsida, Pteropsida (classification order).

• Psilopsida = simplest, no roots.

• Lycopsida = club mosses, roots present.

• Sphenopsida = horsetails, ridged stems.

• Pteropsida = true ferns, sori on leaves.

Quick Checkpoints

• Identify features of each pteridophyte class.

• Which class includes Equisetum?

• Examples of homosporous and heterosporous genera.

Economic Importance of Pteridophytes

Uses

• Food: Sporocarps of Marsilea eaten by some tribes.

• Soil binding: Prevent soil erosion on slopes.

• Scouring: Stems of Equisetum used for cleaning utensils and polishing metals.

• Nitrogen fixation: Azolla forms symbiosis with Anabaena azollae, used as biofertilizer in paddy fields.

• Medicines: Rhizomes of Dryopteris yield anti-helminthic drugs; Equisetum used for diuretic, haemostatic, haemopoietic drugs.

• Ornamental: Ferns grown for attractive foliage, used in bouquets and decorations.

Memory Aids

• Azolla = biofertilizer via nitrogen fixation.

• Equisetum = scouring and medicinal uses.

• Marsilea = edible sporocarps.

• Ferns = ornamental plants.

Quick Checkpoints

• Which pteridophyte is used as biofertilizer?

• Medicinal uses of Dryopteris and Equisetum.

• Role of pteridophytes in soil conservation.

Additional Facts

Key Points

• Term ‘Pteridophyta’ proposed by Haeckel in 1866.

• Study of pteridophytes is called Pteridology.

• Adiantum is called walking fern due to adventitious roots at leaf tips forming new plants.

• Salvinia is rootless pteridophyte, known as “Sorrow of Kashmir”.

• Alsophila is tallest pteridophyte; Azolla is smallest aquatic fern.

• Selaginella species can roll into brown balls in dry season and revive with water; called resurrection plants (e.g., S. bryopteris).

Memory Aids

• Walking fern = Adiantum.

• Resurrection plant = Selaginella.

• Rootless pteridophyte = Salvinia.

Quick Checkpoints

• Who proposed the term Pteridophyta?

• Why is Adiantum called walking fern?

• Identify the smallest and tallest pteridophytes.

Gymnosperms

General Characteristics

Features of Gymnosperms

• Ovules are exposed, not enclosed by ovary wall; seeds are naked.

• Include medium to tall trees and shrubs; e.g., Sequoia (giant redwood) is very tall.

• Roots usually tap roots; some have mycorrhizal association (Pinus), others have coralloid roots with nitrogen-fixing cyanobacteria (Cycas).

• Stems may be unbranched (Cycas) or branched (Pinus, Cedrus).

• Leaves simple or compound; Cycas has persistent pinnate leaves.

• Leaves adapted to extreme conditions: needle-like in conifers, thick cuticle, sunken stomata reduce water loss.

Memory Aids

• Gymnosperms = \"naked seeds\" (no ovary).

• Sequoia = tallest tree.

• Pinus roots + mycorrhiza; Cycas roots + cyanobacteria.

• Needle leaves = water conservation.

Quick Checkpoints

• What type of roots do gymnosperms have?

• How are gymnosperm leaves adapted to dry conditions?

• Which gymnosperm is known as the tallest tree?

Reproductive Structures

Key Points on Gymnosperm Reproduction

• Gymnosperms are heterosporous: produce microspores (male) and megaspores (female).

• Spores develop in sporangia on sporophylls arranged spirally to form cones (strobili).

• Male cones (microsporangiate strobili) bear microsporophylls and microsporangia; microspores develop into pollen grains (male gametophyte).

• Female cones (megasporangiate strobili) bear megasporophylls with ovules; ovule = nucellus + protective envelopes.

• Megaspore mother cell in nucellus undergoes meiosis to form four megaspores; one develops into multicellular female gametophyte with archegonia.

• Male and female gametophytes remain within sporangia on sporophyte; no free-living gametophyte stage.

• Pollen grains released, carried by wind to ovule opening; pollen tube delivers male gametes to archegonia for fertilization.

• Post-fertilization: zygote forms embryo; ovule develops into seed.

• Gymnosperms classified into four groups: Cycadopsida, Ginkgopsida, Coniferopsida, Gnetopsida.

Memory Aids

• Heterosporous = two spore types: micro (male), mega (female).

• Cones = strobili; male = microsporangiate, female = megasporangiate.

• Pollen grain = reduced male gametophyte.

• Female gametophyte retained inside ovule.

• Fertilization via pollen tube.

Quick Checkpoints

• Define heterospory in gymnosperms.

• Where does pollen grain develop?

• What is the structure of an ovule?

• How is fertilization achieved in gymnosperms?

• Name the four gymnosperm groups.

Economic Importance

Uses of Gymnosperms

• Edible seeds: Pinus gerardiana seeds eaten after roasting.

• Timber: wood used for light furniture, plywood, railway sleepers.

• Paper: wood from Picea, Pinus, Larix, Abies used in paper manufacture.

• Linoleum: sawdust used in linoleum and plastics production.

• Ephedrine: drug from Ephedra used to treat respiratory ailments.

• Resin: extracted commercially; distilled to turpentine (solvent) and rosin (waterproofing, writing paper).

Memory Aids

• Pinus seeds = edible.

• Gymnosperm wood = timber and paper.

• Ephedra = source of ephedrine drug.

• Resin products = turpentine and rosin.

Quick Checkpoints

• Which gymnosperm seeds are edible?

• List major uses of gymnosperm wood.

• What is ephedrine used for?

• What products are obtained from resin?

Special Adaptations

Adaptations and Features

• Gymnosperms grow on mountain slopes in cold regions; show xerophytic adaptations.

• All are vascular plants with xylem and phloem; xylem lacks vessels, phloem lacks companion cells.

• Exceptions: Gnetum, Ephedra, Welwitschia have true vessels in xylem.

• Secondary growth occurs; stems are woody.

• Wood is called softwood due to absence of vessels.

• Endosperm is haploid, formed before fertilization.

• Ginkgo biloba known as Maidenhair tree.

• Sequoia known as redwood tree.

• Cycas has largest egg, sperm, and ovule among gymnosperms.

Memory Aids

• Softwood = gymnosperm wood without vessels.

• Xerophytic = adapted to dry, cold habitats.

• Endosperm = haploid, pre-fertilization.

• Maidenhair = Ginkgo biloba.

• Redwood = Sequoia.

Quick Checkpoints

• What type of vascular tissues do gymnosperms have?

• Which gymnosperms have vessels in xylem?

• Why is gymnosperm wood called softwood?

• What is unique about endosperm in gymnosperms?

• Name common names of Ginkgo biloba and Sequoia.

Angiosperms

Overview

• Seed plants with sporophylls arranged into flowers.

• Seeds develop inside fruits.

• Most evolved and dominant plants on Earth.

• Range from tiny Wolffia to tall Eucalyptus trees.

• Provide food, fodder, fuel, medicines, and commercial products.

• Divided into two classes: dicotyledons and monocotyledons.

Memory Aids

• Dicots: Two cotyledons, broad leaves, flower parts in 4s or 5s.

• Monocots: One cotyledon, narrow parallel-veined leaves, flower parts in 3s.

Quick Checkpoints

• What defines angiosperms?

• Difference between dicots and monocots?

• Role of flowers and fruits in angiosperms?

Plant Life Cycles and Alternation of Generations

Overview

• Life cycles follow rigid phase sequences called alternation of generations.

• Three types: haplontic, diplontic, haplodiplontic.

Memory Aids

• Alternation of generations means alternating haploid and diploid phases.

• Haplontic: dominant haploid phase.

• Diplontic: dominant diploid phase.

• Haplodiplontic: both phases multicellular and distinct.

Quick Checkpoints

• What is alternation of generations?

• Identify the three life cycle types.

Haplontic Life Cycle

Characteristics

• Single haploid vegetative phase (gametophyte).

• Gametophyte produces haploid gametes.

• Gametes fuse to form diploid zygote (single-celled).

• Zygote does not form multicellular diploid phase.

• Meiosis occurs during zygote germination producing haploid spores.

• No alternation of generations; sporophyte is only the zygote.

• Examples: algae like Volvox, Spirogyra, Chlamydomonas.

Memory Aids

• Haploid dominant, diploid stage brief and unicellular.

• Think: \"Haploid life, zygote brief\".

Quick Checkpoints

• Which phase is dominant in haplontic cycle?

• What happens to the zygote?

• Examples of organisms with haplontic cycle?

Diplontic Life Cycle

Characteristics

• Single diploid vegetative phase (sporophyte).

• Sporophyte produces haploid gametes via meiosis in sex organs.

• Gametes are the only haploid stage.

• Gametes fuse to form diploid zygote, which grows into sporophyte.

• Occurs in Fucus, Cladophora, gymnosperms, and angiosperms (with reduced gametophyte).

Memory Aids

• Diploid dominant, haploid stage only gametes.

• Think: \"Diploid life, gametes brief\".

Quick Checkpoints

• Which phase is dominant in diplontic cycle?

• When does meiosis occur?

• Examples of diplontic organisms?

Haplodiplontic Life Cycle

Characteristics

• Two multicellular somatic phases: haploid gametophyte and diploid sporophyte.

• Sporophyte (2n) undergoes meiosis to produce haploid spores.

• Haploid spores germinate into gametophytes (n).

• Gametophytes produce gametes; gametes fuse to form diploid zygote.

• Clear alternation of generations between gametophyte and sporophyte.

• Occurs in bryophytes, pteridophytes, and some algae like Dictyota, Ectocarpus, Polysiphonia, kelps.

Memory Aids

• Both haploid and diploid phases multicellular and distinct.

• Think: \"Alternation of generations\".

Quick Checkpoints

• What are the two phases in haplodiplontic cycle?

• Where does meiosis occur?

• Examples of haplodiplontic organisms?

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