Class 11 Biology Notes Chapter 3 (Chapter 3) – Examplar Problems (English) Book
Detailed Notes with MCQs of Chapter 3, 'Plant Kingdom', from your NCERT Exemplar. This is a crucial chapter for competitive exams as it lays the foundation for understanding plant diversity, evolution, and life cycles. Pay close attention to the classification, key characteristics, and examples.
Chapter 3: Plant Kingdom - Detailed Notes for Competitive Exams
1. Systems of Classification:
- Artificial Systems: Based on superficial morphological characters (e.g., habit, colour, number, and shape of leaves).
- Example: Linnaeus's system (based on androecium structure).
- Drawback: Gave equal weightage to vegetative and sexual characteristics; separated closely related species.
- Natural Systems: Based on natural affinities among organisms, considering both external and internal features (ultrastructure, anatomy, embryology, phytochemistry).
- Example: Bentham and Hooker's system (for flowering plants).
- Advantage: Better reflects natural relationships.
- Phylogenetic Systems: Based on evolutionary relationships between organisms. Assumes organisms in the same taxa have a common ancestor.
- Uses data from fossil records, numerical taxonomy, cytotaxonomy, and chemotaxonomy.
- Example: Engler and Prantl, Hutchinson.
- Numerical Taxonomy: Uses computer analysis of observable characters, assigning numbers/codes and equal importance to each.
- Cytotaxonomy: Based on cytological information (chromosome number, structure, behaviour).
- Chemotaxonomy: Uses chemical constituents (e.g., secondary metabolites) to resolve taxonomic confusion.
2. Algae (Thallophyta):
- General Characteristics:
- Chlorophyll-bearing, simple, thalloid (undifferentiated body), autotrophic.
- Largely aquatic (freshwater and marine). Also found in moist stones, soils, wood, association with fungi (Lichens) and animals (e.g., on sloth bear).
- Size/Form: Highly variable (microscopic unicellular like Chlamydomonas to colonial like Volvox, filamentous like Ulothrix, Spirogyra, and massive plant bodies like Kelps).
- Reproduction:
- Vegetative: Fragmentation.
- Asexual: Spores (most common: zoospores - flagellated, motile).
- Sexual: Fusion of gametes.
- Isogamous: Fusion of similar-sized gametes (flagellated: Chlamydomonas; non-flagellated: Spirogyra).
- Anisogamous: Fusion of two dissimilar-sized gametes (e.g., some species of Chlamydomonas).
- Oogamous: Fusion between one large, non-motile female gamete and a smaller, motile male gamete (e.g., Volvox, Fucus).
- Classification (based on pigment type & stored food):
- Chlorophyceae (Green Algae):
- Pigments: Chlorophyll a, b (dominant). Carotenoids.
- Stored Food: Starch. Some store oil droplets.
- Cell Wall: Inner cellulose, outer pectose.
- Chloroplasts: Diverse shapes (discoid, plate-like, reticulate, cup-shaped, spiral/ribbon-shaped).
- Storage Bodies: Pyrenoids (contain protein besides starch), located in chloroplasts.
- Flagella: 2-8, equal, apical.
- Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara.
- Phaeophyceae (Brown Algae):
- Habitat: Primarily marine.
- Pigments: Chlorophyll a, c, carotenoids, xanthophylls (dominant: fucoxanthin - gives olive green to brown colour).
- Stored Food: Complex carbohydrates (laminarin or mannitol).
- Cell Wall: Cellulose, usually covered by a gelatinous coating of algin.
- Body: Simple branched, filamentous (Ectocarpus) to profusely branched forms like kelps (up to 100m). Body differentiated into holdfast (attachment), stipe (stalk), and frond (leaf-like photosynthetic organ).
- Flagella: 2, unequal, laterally inserted.
- Examples: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus.
- Rhodophyceae (Red Algae):
- Habitat: Mostly marine, greater concentrations in warmer areas. Found in well-lighted regions close to the surface and also at great depths where little light penetrates.
- Pigments: Chlorophyll a, d, phycoerythrin (dominant: r-phycoerythrin - gives red colour).
- Stored Food: Floridean starch (structure similar to amylopectin and glycogen).
- Cell Wall: Cellulose, pectins, and polysulphate esters.
- Body: Mostly multicellular; some have complex body organisation.
- Reproduction: Asexual by non-motile spores; Sexual is oogamous, complex post-fertilization developments. Motile stages absent.
- Examples: Polysiphonia, Porphyra, Gracilaria, Gelidium.
- Chlorophyceae (Green Algae):
- Economic Importance of Algae:
- Photosynthesis: Fix half of Earth's total CO2. Primary producers.
- Food: Porphyra, Laminaria, Sargassum are edible.
- Hydrocolloids (water-holding substances):
- Algin (Brown algae)
- Carrageen (Red algae)
- Agar: From Gelidium and Gracilaria (used in microbial cultures, ice-creams, jellies).
- Food Supplements: Chlorella, Spirulina (unicellular, rich in protein, used by space travellers).
3. Bryophytes (Amphibians of the Plant Kingdom):
- General Characteristics:
- Habitat: Damp, humid, shaded localities. Depend on water for sexual reproduction.
- Body: Thallus-like, prostrate or erect. Attached by unicellular or multicellular rhizoids. Lack true roots, stem, or leaves but may possess root-like, leaf-like, or stem-like structures.
- Dominant Phase: Gametophyte (haploid, independent, photosynthetic).
- Sporophyte: Multicellular, dependent (partially or wholly) on the gametophyte for anchorage and nutrition. Differentiated into foot, seta, and capsule. Produces haploid spores via meiosis.
- Vascular Tissues: Absent (no xylem, phloem).
- Reproduction:
- Vegetative: Fragmentation, budding (secondary protonema), gemmae (in liverworts).
- Sexual: Main plant body is gametophyte (n). Sex organs are multicellular.
- Antheridium (male): Produces biflagellate antherozoids.
- Archegonium (female, flask-shaped): Produces a single egg.
- Fertilization: Requires water for antherozoid transfer. Zygote (2n) develops into a sporophyte (2n).
- Life Cycle: Haplodiplontic (dominant gametophyte).
- Classification:
- Liverworts:
- Habitat: Moist, shady habitats (banks of streams, marshy ground, damp soil, bark of trees, deep in woods).
- Body: Thalloid (e.g., Marchantia) or leafy members with tiny leaf-like appendages (Porella).
- Asexual Reproduction: Fragmentation, gemmae (green, multicellular buds in gemma cups).
- Sexual Reproduction: Antheridia and archegonia produced on the same or different thalli. Sporophyte differentiated into foot, seta, capsule.
- Mosses:
- Life Cycle Stages:
- Protonema stage (juvenile): Develops directly from a spore. Creeping, green, branched, filamentous.
- Leafy stage (mature): Develops from secondary protonema as a lateral bud. Upright, slender axis bearing spirally arranged leaves. Attached by multicellular, branched rhizoids. Bears sex organs.
- Vegetative Reproduction: Fragmentation, budding in secondary protonema.
- Sexual Reproduction: Antheridia and archegonia at the apex of leafy shoots. Sporophyte more elaborate than liverworts (foot, seta, capsule). Spore dispersal mechanism is elaborate (involves peristome teeth).
- Examples: Funaria, Polytrichum, Sphagnum.
- Life Cycle Stages:
- Liverworts:
- Economic Importance:
- Limited economic importance but significant ecological importance.
- Pioneer colonizers on bare rocks/soil (with lichens). Decompose rock, make substrate suitable for higher plants (Ecological Succession).
- Form dense mats on soil, reducing soil erosion.
- Sphagnum (peat moss): Provides peat (fuel). High water-holding capacity makes it useful as packing material for trans-shipment of living material.
4. Pteridophytes (First Terrestrial Vascular Plants):
- General Characteristics:
- Habitat: Cool, damp, shady places. Some flourish well in sandy-soil conditions.
- Evolutionary Significance: First terrestrial plants to possess vascular tissues (xylem and phloem).
- Dominant Phase: Sporophyte (diploid, independent, photosynthetic). Differentiated into true root, stem, and leaves.
- Leaves: Small (microphylls) as in Selaginella or large (macrophylls) as in Ferns.
- Sporophylls: Leaves bearing sporangia. May form distinct compact structures called strobili or cones (Selaginella, Equisetum).
- Gametophyte (Prothallus): Small, inconspicuous, multicellular, free-living, mostly photosynthetic, thalloid. Requires cool, damp, shady places to grow. Restricted narrow geographical distribution due to need for water for fertilization.
- Reproduction:
- Sporophyte produces spores (haploid) by meiosis in sporangia.
- Spores germinate into gametophyte (prothallus).
- Homosporous: Produce spores of similar kinds (most pteridophytes, e.g., Pteris, Dryopteris). Gametophyte is monoecious (bears both antheridia and archegonia).
- Heterosporous: Produce two kinds of spores - microspores (male) and megaspores (female) (e.g., Selaginella, Salvinia). Gametophytes are dioecious. Female gametophyte retained on parent sporophyte for variable periods. Development of zygote into young embryo takes place within the female gametophyte (precursor to seed habit).
- Sexual Reproduction: Gametophyte bears antheridia and archegonia. Water needed for transfer of antherozoids (flagellated) to archegonium. Zygote (2n) develops into a multicellular, well-differentiated sporophyte.
- Life Cycle: Haplodiplontic (dominant sporophyte).
- Classification (Major Classes):
- Psilopsida (e.g., Psilotum)
- Lycopsida (e.g., Selaginella, Lycopodium)
- Sphenopsida (e.g., Equisetum - Horsetail)
- Pteropsida (e.g., Dryopteris, Pteris, Adiantum - Ferns)
- Economic Importance:
- Medicinal purposes.
- Soil binders.
- Ornamentals (Ferns are widely grown).
5. Gymnosperms (Naked Seed Plants):
- General Characteristics:
- Plants in which ovules are not enclosed by any ovary wall and remain exposed, both before and after fertilization. Seeds developed post-fertilization are naked.
- Includes medium-sized trees or tall trees and shrubs. Sequoia (giant redwood) is one of the tallest tree species.
- Roots: Generally tap roots. Roots in some have fungal association (mycorrhiza - Pinus) or specialized nitrogen-fixing cyanobacteria (Coralloid roots - Cycas).
- Stem: Unbranched (Cycas) or branched (Pinus, Cedrus).
- Leaves: Simple or compound. Well-adapted to withstand extremes of temperature, humidity, and wind.
- In conifers (Pinus), needle-like leaves reduce surface area. Thick cuticle and sunken stomata reduce water loss.
- Reproduction:
- Heterosporous: Produce haploid microspores and megaspores.
- Spores produced within sporangia borne on sporophylls, arranged spirally along an axis to form compact strobili or cones.
- Microsporangiate (Male strobili): Bear microsporophylls with microsporangia. Microspores develop into male gametophyte (highly reduced, confined to a limited number of cells = Pollen grain).
- Megasporangiate (Female strobili): Bear megasporophylls with megasporangia (ovules). Megaspore mother cell (in nucellus) divides meiotically to form four megaspores. One megaspore develops into a multicellular female gametophyte bearing two or more archegonia.
- Pollination: Air currents carry pollen grains to the opening of the ovules.
- Fertilization: Pollen tube carrying male gametes grows towards archegonia in the ovules and discharges contents near the mouth of the archegonia. Zygote develops into an embryo.
- Seed: Ovule develops into a seed (naked).
- Gametophytes (male and female) do not have an independent free-living existence; remain within the sporangia retained on the sporophyte.
- Life Cycle: Diplontic (dominant sporophyte).
- Examples: Cycas, Pinus, Cedrus, Ginkgo, Sequoia.
6. Angiosperms (Flowering Plants):
- Covered seeds (ovules develop within ovary, which matures into fruit).
- Flowers are the reproductive structures.
- Highly diverse group. Size ranges from tiny Wolffia to tall Eucalyptus.
- Double Fertilization: Unique event where one male gamete fuses with the egg (syngamy) to form the zygote (2n), and the other male gamete fuses with the diploid secondary nucleus (triple fusion) to form the primary endosperm nucleus (PEN, 3n), which develops into endosperm (nutritive tissue).
- Divided into Dicotyledons and Monocotyledons. (Details in later chapters).
7. Plant Life Cycles and Alternation of Generations:
- Plants exhibit alternation between haploid gametophyte (n) and diploid sporophyte (2n) generations.
- Haplontic Life Cycle:
- Dominant phase is the free-living, photosynthetic gametophyte (n).
- Sporophyte generation represented only by the one-celled zygote (2n).
- Meiosis occurs in the zygote (zygotic meiosis), resulting in haploid spores that form the gametophyte.
- Examples: Many algae like Volvox, Spirogyra, some Chlamydomonas species.
- Diplontic Life Cycle:
- Dominant phase is the diploid sporophyte (2n), which is photosynthetic and independent.
- Gametophytic phase is represented by the single to few-celled haploid gametophyte (dependent on sporophyte).
- Meiosis occurs during gamete formation (gametic meiosis).
- Examples: All seed-bearing plants (Gymnosperms and Angiosperms), Fucus (alga).
- Haplodiplontic Life Cycle:
- Intermediate condition; both gametophyte (n) and sporophyte (2n) phases are multicellular and often free-living (but may differ in dominant phase).
- Meiosis occurs in the sporophyte to produce haploid spores (sporic meiosis).
- Examples: Bryophytes (dominant gametophyte), Pteridophytes (dominant sporophyte). Most algae like Ectocarpus, Polysiphonia, Kelps exhibit this pattern.
Key Points for Exams:
- Know the basis and examples of different classification systems.
- Memorize key characteristics, pigments, stored food, and examples of algal classes.
- Understand the economic importance of algae (Agar, Algin, Carrageen, SCP).
- Bryophytes as 'Amphibians', dominant gametophyte, absence of vascular tissue, Sphagnum importance.
- Pteridophytes as 'first vascular plants', dominant sporophyte, homospory vs. heterospory (examples!), precursor to seed habit.
- Gymnosperms 'naked seeds', characteristics of Pinus and Cycas (mycorrhiza, coralloid roots, branched/unbranched stem), adaptations for xerophytic conditions, pollination mechanism.
- Clearly differentiate between Haplontic, Diplontic, and Haplodiplontic life cycles with examples.
- Understand the concept of Alternation of Generations in each plant group.
Multiple Choice Questions (MCQs):
-
Which of the following classification systems is based on evolutionary relationships between various organisms?
a) Artificial system
b) Natural system
c) Phylogenetic system
d) Numerical taxonomy -
Floridean starch as reserve food material and phycoerythrin as the major pigment are characteristic features of:
a) Chlorophyceae
b) Phaeophyceae
c) Rhodophyceae
d) Cyanophyceae -
In Bryophytes, the dominant phase of the life cycle is the _______ and the _______ is dependent on it.
a) Sporophyte, Gametophyte
b) Gametophyte, Sporophyte
c) Gametophyte, Antheridium
d) Sporophyte, Archegonium -
Which of the following Pteridophytes is heterosporous?
a) Dryopteris
b) Adiantum
c) Equisetum
d) Selaginella -
Coralloid roots, having a symbiotic association with N2-fixing cyanobacteria, are found in:
a) Pinus
b) Cycas
c) Cedrus
d) Sequoia -
Agar, commonly used in microbiological culture media, is obtained from:
a) Ulothrix and Spirogyra
b) Gelidium and Gracilaria
c) Laminaria and Sargassum
d) Fucus and Dictyota -
Which plant group first evolved vascular tissues (xylem and phloem)?
a) Algae
b) Bryophytes
c) Pteridophytes
d) Gymnosperms -
A plant shows a thallus level of organization. It is haploid and needs water to complete its life cycle because the male gametes are motile. It could belong to:
a) Pteridophytes
b) Gymnosperms
c) Monocots
d) Bryophytes -
The unique event of double fertilization is characteristic of:
a) Algae
b) Gymnosperms
c) Angiosperms
d) Pteridophytes -
A plant exhibits a haplontic life cycle. Which stage undergoes meiosis?
a) Gamete
b) Spore
c) Gametophyte
d) Zygote
Answer Key for MCQs:
- c) Phylogenetic system
- c) Rhodophyceae
- b) Gametophyte, Sporophyte
- d) Selaginella
- b) Cycas
- b) Gelidium and Gracilaria
- c) Pteridophytes
- d) Bryophytes
- c) Angiosperms
- d) Zygote
Study these notes thoroughly, focusing on the distinguishing features and life cycle patterns. Remember to correlate these concepts with diagrams from your NCERT book for better understanding. Good luck with your preparation!