Chapter 2: Plant Kingdom

Plant Kingdom

Classification and Characteristics

• Kingdom Plantae: multicellular, photosynthetic, aquatic or terrestrial.
• Divided into Cryptogamae (no seeds) and Phanerogamae (with seeds).
• Cryptogamae: Thallophyta (algae, no vascular tissue), Bryophyta (mosses, non-vascular), Pteridophyta (ferns, vascular but no seeds).
• Phanerogamae: Gymnospermae (naked seeds, no flowers), Angiospermae (seeds in fruits, flowering plants).
• Classification evolved from artificial (Linnaeus) to natural (Bentham & Hooker) to phylogenetic systems.
• Modern taxonomy includes numerical taxonomy, cytotaxonomy, and chemotaxonomy.

Memory Aids

• Cryptogamae = "hidden seeds" (no seeds).
• Phanerogamae = "visible seeds" (seed plants).
• Artificial systems focus on few traits; natural systems consider anatomy and chemistry.

Quick Checkpoints

• What are the two main groups of Kingdom Plantae?
• Which group has vascular tissue but no seeds?
• Who proposed the natural classification system?
• What is the basis of phylogenetic classification?

Algae

General Characteristics

• Simple, autotrophic, mostly aquatic organisms with chlorophyll.
• Habitat: freshwater, marine, moist terrestrial, symbiotic (e.g., lichens).
• Unusual habitats: halophytic, epiphytic, epizoic, endozoic, parasitic, thermophytic algae.
• Forms: unicellular (motile/non-motile), colonial, filamentous, large kelps.
• Thallus: vegetative body; cell wall has cellulose (inner) and pectin (outer).
• Photosynthetic pigments: chlorophyll a (all), b, c, d; carotenoids (carotenes, xanthophylls); phycobilins (phycocyanins, phycoerythrins).
• Food reserves: starch, laminarin, mannitol, floridean starch.
• Reproduction: vegetative (fragmentation), asexual (zoospores), sexual (isogamy, anisogamy, oogamy).

Memory Aids

• Isogamy: gametes alike; Anisogamy: gametes differ in size; Oogamy: large non-motile egg, small motile sperm.
• Kelps = large brown algae, "trees of the sea".
• Thallus = algal body without differentiation.

Quick Checkpoints

• What pigments are common to all algae?
• Name three types of sexual reproduction in algae.
• What is the vegetative body of algae called?
• Which algae live in hot water springs?

Classification of Algae

Classes and Features

• Based on phylogeny and affinities, algae classified by Dr. F. E. Fritsch and Whittaker.
• Main classes: Chlorophyceae (green algae), Phaeophyceae (brown algae), Rhodophyceae (red algae).
• Chlorophyceae: unicellular/colonial/filamentous; chlorophyll a & b; pyrenoids store protein & starch; cell wall cellulose + pectose; reproduction by fragmentation, flagellated zoospores, sexual types.
• Phaeophyceae: marine; from filamentous to large kelps; pigments chlorophyll a, carotenoids, xanthophylls (fucoxanthin); plant body with holdfast, stipe, frond; reproduction by fragmentation, biflagellate zoospores, sexual types.
• Rhodophyceae: red pigment phycoerythrin; found near surface and deep water; food stored as floridean starch; multicellular thalli; reproduction vegetative by fragmentation, asexual non-motile spores, oogamous sexual reproduction.

Memory Aids

• Chlorophyceae = green, chlorophyll a & b, pyrenoids present.
• Phaeophyceae = brown, fucoxanthin pigment, kelps are large.
• Rhodophyceae = red, phycoerythrin pigment, floridean starch.

Quick Checkpoints

• Which class of algae has pyrenoids?
• What pigment gives brown algae their color?
• Where are red algae found in water?
• What type of spores do red algae produce asexually?

Economic Importance of Algae

Uses and Benefits

• Food: Porphyra, Laminaria, Sargassum; Chlorella rich in protein supplement.
• Photosynthesis: contributes ~50% of Earth's photosynthesis; vital for aquatic respiration.
• Phycocolloids: Alginic acid (from brown algae) used in emulsions, plastics, security glass.
• Agar-agar: from red algae, used as solidifying agent in culture media.
• Carrageen: from red algae, used in pharmaceuticals, textiles, leather, brewing.
• Medicines: Red algae Corallina (anti-worm), brown algae Laminaria & Ascophyllum (antibiotics), Durvillea (vermifuge), green algae Chlorella & Caulerpa (antibiotics).
• Sewage disposal: green algae like Chlamydomonas, Chlorella, Scenedesmus aid aerobic sewage treatment.

Memory Aids

• Phycology = study of algae.
• Algae = non-embryophytes, no embryo, unicellular sex organs.
• Macrocystis pyrifera = largest algae; Laminaria = Devil's Apron.
• Spirogyra = pond silk due to mucilage shine.

Quick Checkpoints

• Name a protein-rich algae used as food supplement.
• What phycocolloid is extracted from brown algae?
• Which algae help in sewage treatment?
• What is the study of algae called?

General Characteristics

Features

• Bryophytes are called amphibians of the plant kingdom; live on soil but need water for sexual reproduction.
• Found in damp, humid, shaded places; 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 root-like, leaf-like, or stem-like structures.
• Main plant body is haploid gametophyte producing gametes.
• Sex organs are multicellular: male antheridium produces biflagellate antherozoids; female archegonium is flask-shaped producing one 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 gametophyte, completing life cycle.

Memory Aids

• Amphibians of plants = need water for reproduction.
• Gametophyte = dominant haploid stage.
• Antheridium = male; Archegonium = female.
• Sporophyte depends on gametophyte.

Quick Checkpoints

• Why are bryophytes called amphibians of the plant kingdom?
• What is the dominant stage in bryophytes?
• Describe the structure and function of sex organs in bryophytes.
• How does sporophyte depend on gametophyte?

Liverworts

Characteristics and Reproduction

• 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 types have tiny leaf-like appendages in two rows on stem-like structures.
• Asexual reproduction by fragmentation of thalli or by 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 in capsule.
• Spores germinate into free-living gametophytes.

Memory Aids

• Gemmae = asexual buds in gemma cups.
• Marchantia = common thalloid liverwort.
• Sporophyte parts: foot, seta, capsule.

Quick Checkpoints

• Where do liverworts commonly grow?
• How do gemmae help in asexual reproduction?
• What are the parts of the sporophyte in liverworts?

Mosses

Life Cycle and Reproduction

• Dominant stage is gametophyte with two stages: protonema and leafy stage.
• Protonema: creeping, green, branched, filamentous stage from spore.
• Leafy stage: develops from lateral bud on secondary protonema; upright axes with spirally arranged leaves.
• Attached to soil by multicellular, branched rhizoids.
• Sex organs (antheridia and archegonia) at apex of leafy shoots.
• Vegetative reproduction by fragmentation and budding in secondary protonema.
• After fertilization, zygote forms sporophyte with foot, seta, and capsule containing spores.
• Common mosses: Funaria, Polytrichum, Sphagnum.

Memory Aids

• Protonema = first stage, filamentous growth.
• Leafy stage bears sex organs.
• Sporophyte parts: foot, seta, capsule.
• Funaria = common moss example.

Quick Checkpoints

• What are the two stages of moss gametophyte?
• How does vegetative reproduction occur in mosses?
• Describe the sporophyte structure in mosses.

Economic Importance of Bryophytes

Uses and Benefits

• Prevention of soil erosion: Mosses form dense mats reducing soil erosion by water and rain impact.
• Soil formation: Bryophytes aid ecological succession and soil formation on rocks (e.g., Sphagnum fills ponds).
• Water retention: Some mosses like Sphagnum absorb 18-26 times their weight in water; used in gardening and plant transport.
• Peat formation: Dead mosses in acidic marshes form peat, used as manure, fuel, and to improve soil aeration and water retention.
• Ecological importance: Mosses and lichens are pioneer colonizers of rocks.

Memory Aids

• Sphagnum = water absorber and peat source.
• Peat = fossilized moss, used as fuel and manure.
• Moss mats prevent soil erosion.

Quick Checkpoints

• How do bryophytes prevent soil erosion?
• What role do bryophytes play in soil formation?
• Why is Sphagnum important in water retention?
• What is peat and its uses?

Additional Facts

Key Points

• Study of bryophytes is called Bryology.
• Tallest bryophytes can reach 70 cm (e.g., Dawsonia).
• Polytrichum is known as hair cap moss.
• Sphagnum is 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.
• Which moss is called hair cap moss?
• Why is Sphagnum called famine food?

General Characteristics

Overview

• Pteridophytes include horsetails and ferns; used medicinally, as soil-binders, and ornamentals.
• First terrestrial plants with vascular tissues (xylem and phloem).
• Found mostly in cool, damp, shady places; some thrive in sandy soils.

Plant Body and Reproduction

• Main plant body is a 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).
• Sporangia produce spores by meiosis; spores germinate into free-living, photosynthetic gametophytes called prothallus.
• Gametophytes require cool, damp, shady conditions; bear antheridia (male) and archegonia (female).
• Water is essential for antherozoid transfer to archegonium; fertilization forms zygote, which grows into dominant sporophyte.
• Most pteridophytes are homosporous (one spore type); some like Selaginella and Salvinia are heterosporous (macro- and microspores).
• Heterosporous plants retain female gametophytes on sporophyte; embryo development inside female gametophyte is a precursor to seed habit.

Memory Aids

• Pteridophytes = First vascular plants without seeds.
• Sporophyte dominant, gametophyte free-living and photosynthetic.
• Homosporous = one spore type; heterosporous = two spore types.
• Water needed for fertilization.

Quick Checkpoints

• What are the main organs of pteridophyte sporophyte?
• Define sporophyll and strobili.
• Explain the role of water in fertilization.
• Difference between homosporous and heterosporous pteridophytes.

Classification of Pteridophytes

Classes and Features

• Psilopsida: Oldest, simplest vascular plants; no roots, have rhizoids; all extinct; e.g., Psilotum.
• Lycopsida: Club mosses/spike mosses; have roots, stems, leaves; homosporous or heterosporous; e.g., Lycopodium, Selaginella.
• Sphenopsida: Stems with ridges/grooves; small leaves in whorls; always homosporous; e.g., Equisetum.
• Pteropsida: Largest, most advanced; mostly lack aerial stem except tree ferns; spores in sori on leaves; homosporous or heterosporous; e.g., Dryopteris, Marsilea.

Memory Aids

• Four classes: Psilopsida (primitive), Lycopsida (club mosses), Sphenopsida (horsetails), Pteropsida (ferns).
• Psilopsida extinct; Lycopsida includes heterosporous plants.
• Sphenopsida always homosporous; Pteropsida most diverse.

Quick Checkpoints

• Name the four classes of pteridophytes.
• Which class is extinct?
• Identify homosporous and heterosporous classes.
• Examples of each class.

Economic Importance of Pteridophytes

Uses

• Food: Sporocarps of Marsilea eaten by some tribal communities.
• Soil binding: Prevent soil erosion on hill slopes.
• Scouring: Stems of Equisetum used for cleaning utensils and polishing metals.
• Nitrogen fixation: Water fern Azolla forms symbiosis with nitrogen-fixing cyanobacteria; used as biofertilizer in paddy fields.
• Medicines: Rhizomes of male shield fern (Dryopteris) yield anti-helminthic drugs; Equisetum used for diuretic, haemostatic, and haemopoietic drugs.
• Ornamental: Ferns grown for attractive foliage; used in bouquets and decorations.

Memory Aids

• Marsilea for food; Equisetum for scouring and medicine.
• Azolla fixes nitrogen; used as biofertilizer.
• Ferns popular as ornamental plants.

Quick Checkpoints

• List economic uses of pteridophytes.
• Which pteridophyte is used as biofertilizer?
• Name medicinal uses of pteridophytes.
• Why are ferns grown ornamentally?

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 from leaf tips.
• Salvinia is rootless and known as “Sorrow of Kashmir.”
• Alsophila is the tallest pteridophyte; Azolla is the smallest aquatic fern.
• Selaginella species are resurrection plants; dry brown balls revive with water (e.g., S. bryopteris).

Memory Aids

• Pteridophyta named by Haeckel; study called Pteridology.
• Walking fern = Adiantum.
• Rootless fern = Salvinia.
• Tallest = Alsophila, smallest = Azolla.
• Resurrection plant = Selaginella.

Quick Checkpoints

• Who proposed the term Pteridophyta?
• What is Pteridology?
• Why is Adiantum called walking fern?
• Which pteridophyte is rootless?
• Identify the tallest and smallest pteridophytes.
• What are resurrection plants?

General Characteristics

Features

• Gymnosperms have naked ovules exposed before and after fertilisation.
• Include medium to tall trees and shrubs; e.g., Sequoia (giant redwood) is very tall.
• Roots are mostly tap roots; some have mycorrhizal association (Pinus), others have coralloid roots with nitrogen-fixing cyanobacteria (Cycas).
• Stems can be unbranched (Cycas) or branched (Pinus, Cedrus).
• Leaves are simple or compound; Cycas has persistent pinnate leaves.
• Leaves adapted to extreme conditions: needle-like with thick cuticle and sunken stomata to reduce water loss.

Memory Aids

• Gymnosperms = "naked seeds" (no ovary covering).
• Needle leaves = less water loss.
• Sequoia = tallest tree.

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

• Gymnosperms are heterosporous: produce microspores (male) and megaspores (female).
• Spores develop in sporangia on sporophylls arranged in cones (strobili).
• Male cones (microsporangiate strobili) produce pollen grains (reduced male gametophyte).
• Female cones (megasporangiate strobili) bear ovules; ovule = nucellus + envelopes.
• Megaspore mother cell undergoes meiosis → 4 megaspores; one develops into female gametophyte with archegonia inside ovule.
• Male and female gametophytes remain inside sporophyte; no free-living gametophytes.
• Pollen grains released, carried by wind to ovules; pollen tube delivers male gametes to archegonia.
• Fertilisation forms zygote → embryo; ovule develops into seed.
• Four gymnosperm groups: Cycadopsida, Ginkgopsida, Coniferopsida, Gnetopsida.

Memory Aids

• Heterosporous = two spore types → male (pollen) and female (ovule).
• Cones = strobili; male = microsporangiate, female = megasporangiate.
• Pollen grain = reduced male gametophyte.

Quick Checkpoints

• What are the two types of spores in gymnosperms?
• Where do pollen grains develop?
• What is the structure called that bears ovules?
• How is fertilisation achieved in gymnosperms?

Economic Importance

Uses

• Edible seeds: Pinus gerardiana seeds are edible after roasting.
• Timber: 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 for respiratory ailments.
• Resin: Extracted for turpentine (solvent) and rosin (waterproofing, paper).

Memory Aids

• Pinus seeds = edible nuts.
• Ephedra = source of ephedrine drug.
• Resin products = turpentine and rosin.

Quick Checkpoints

• Which gymnosperm seeds are edible?
• What are the main uses of gymnosperm wood?
• From which plant is ephedrine obtained?
• What are the products obtained from resin?

Special Adaptations

Adaptations and Features

• Gymnosperms grow on mountain slopes in cold regions; show xerophytic adaptations.
• Vascular plants with xylem and phloem; xylem mostly lacks vessels, phloem lacks companion cells.
• Exceptions with vessels in xylem: Gnetum, Ephedra, Welwitschia.
• Secondary growth occurs; stems are woody but wood is soft due to absence of vessels.
• Endosperm is haploid, formed before fertilisation.
• Ginkgo biloba = Maidenhair tree; Sequoia = Redwood tree.
• Cycas has largest egg, sperm, and ovule among gymnosperms.

Memory Aids

• Xerophytic = adapted to dry, cold mountain slopes.
• Softwood = gymnosperm wood without vessels.
• Ginkgo = Maidenhair tree; Sequoia = Redwood.

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 Cycas reproductive cells?

Angiosperms

Overview

• Seed plants with sporophylls organized 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 seed leaves, broad leaves, flower parts in 4s or 5s.
• Monocots: One seed leaf, narrow parallel-veined leaves, flower parts in 3s.

Quick Checkpoints

• What defines angiosperms?
• Difference between dicots and monocots?
• Examples of smallest and tallest angiosperms?

Plant Life Cycles and Alternation of Generations

Overview

• Life cycles vary among plant groups but follow a strict sequence of phases.
• This sequence is called alternation of generations.
• Three types of life cycles: 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?
• Name the three life cycle types.
• Which phase is dominant in each type?

Haplontic Life Cycle

Characteristics

• Single haploid vegetative phase called gametophyte.
• Gametophyte produces haploid gametes.
• Gametes fuse to form diploid zygote (single-celled).
• Zygote does not form multicellular diploid structure; meiosis occurs at germination.
• Meiosis produces haploid nuclei/spores that develop into new gametophytes.
• No true alternation of generations; sporophyte phase is only the single-celled zygote.
• Examples: algae like Volvox, Spirogyra, Chlamydomonas.

Memory Aids

• Haplo = single set of chromosomes dominant.
• Zygote is brief diploid stage only.

Quick Checkpoints

• What is the dominant phase in haplontic cycle?
• When does meiosis occur?
• Does the zygote form a multicellular sporophyte?

Diplontic Life Cycle

Characteristics

• Single diploid vegetative phase called sporophyte.
• Sporophyte produces haploid gametes via meiosis in sex organs.
• Gametes are the only haploid stage.
• Fertilization produces diploid zygote that grows into sporophyte.
• Occurs in Fucus, Cladophora, and all seed plants (gymnosperms, angiosperms) with some gametophyte variation.

Memory Aids

• Diplo = diploid phase dominant.
• Gametes are haploid but short-lived.

Quick Checkpoints

• Which phase is dominant in diplontic cycle?
• Where does meiosis occur?
• What is the ploidy of gametes?

Haplodiplontic Life Cycle

Characteristics

• Two distinct multicellular phases: haploid gametophyte and diploid sporophyte.
• Sporophyte (2n) undergoes meiosis to produce haploid spores.
• Haploid spores grow 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 are multicellular and independent.
• Alternation of generations is clear and distinct.

Quick Checkpoints

• What are the two phases in haplodiplontic cycle?
• Where does meiosis occur?
• Which phase produces gametes?