Plant Kingdom – Class 11 Biology Chapter 3 Notes & NCERT PDF

Class 11BiologyChapter 3NCERT book: Biology - Class 11

Notes and a simple summary of Chapter 3 of the NCERT Class 11 Biology book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 3: Plant Kingdom

Introduction

This chapter classifies Kingdom Plantae in detail. Fungi, and Monera and Protista with cell walls, are now excluded from Plantae — so cyanobacteria (blue-green algae) are no longer 'algae'. Plantae includes Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms.

Systems of classification

Artificial systems (e.g., Linnaeus, based on androecium): used superficial morphology (habit, colour, number and shape of leaves); gave equal weightage to vegetative and sexual characters — not acceptable, as vegetative characters are easily affected by environment.

Natural systems — based on natural affinities, including internal features (ultrastructure, anatomy, embryology, phytochemistry). Given for flowering plants by George Bentham and Joseph Dalton Hooker.

Phylogenetic systems — based on evolutionary relationships; assume organisms of the same taxa share a common ancestor.

Numerical taxonomy — computer-based; all observable characters given numbers/codes and equal importance.

Cytotaxonomy — uses chromosome number, structure, behaviour. Chemotaxonomy — uses chemical constituents.

Key Concepts

3.1 Algae

Chlorophyll-bearing, simple, thalloid, autotrophic, largely aquatic; also on moist stones, soil, wood; with fungi (lichen) and on animals (sloth bear).

Forms: colonial (Volvox), filamentous (Ulothrix, Spirogyra), massive marine kelps.

Reproduction: vegetative by fragmentation; asexual by spores (commonly zoospores, flagellated); sexual:

- Isogamous — gametes similar in size (flagellated in Ulothrix, non-flagellated in Spirogyra).

- Anisogamous — dissimilar in size (Eudorina).

- Oogamous — large non-motile female + small motile male (Volvox, Fucus).

Usefulness: at least half of total CO₂ fixation on earth; primary producers; about 70 species of marine algae used as food (Porphyra, Laminaria, Sargassum); hydrocolloids — algin (brown algae), carrageen (red algae); agar from Gelidium and Gracilaria (microbe culture, ice-creams, jellies); *Chlorella* — protein-rich food supplement even for space travellers.

#### Three classes (Table 3.1 as lists)

Chlorophyceae (green algae): pigments chlorophyll a, b; stored food starch (in pyrenoids, which also contain protein); wall cellulose (inner) and pectose (outer); flagella 2–8, equal, apical; fresh, brackish and salt water. Chloroplasts discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped. Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara.

Phaeophyceae (brown algae): chlorophyll a, c, fucoxanthin; stored food mannitol, laminarin; wall cellulose with algin coating; flagella 2, unequal, lateral; mostly marine. Body: holdfast, stipe, frond; kelps up to 100 metres; pear-shaped (pyriform) biflagellate zoospores. Examples: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus.

Rhodophyceae (red algae): chlorophyll a, d, r-phycoerythrin; stored food floridean starch (similar to amylopectin and glycogen); wall cellulose, pectin, poly-sulphate esters; flagella absent; mostly marine, warm areas, even at great depths. Sexual reproduction oogamous with complex post-fertilisation development. Examples: Polysiphonia, Porphyra, Gracilaria, Gelidium.

3.2 Bryophytes

Mosses and liverworts; moist shaded areas in hills; called amphibians of the plant kingdom (live in soil but need water for sexual reproduction); important in plant succession on bare rocks.

Plant body thallus-like; attached by rhizoids; lack true roots, stem, leaves.

Main plant body is haploid — the gametophyte.

Sex organs multicellular: antheridium (biflagellate antherozoids) and flask-shaped archegonium (single egg). Fertilisation in water → zygote → multicellular sporophyte (not free-living; attached to and nourished by the gametophyte) → meiosis → haploid spores → gametophyte.

Economic/ecological importance: food for animals; *Sphagnum* gives peat (fuel, packing material due to water-holding capacity); with lichens, first colonisers of rocks; prevent soil erosion.

3.2.1 Liverworts — thalloid, dorsiventral (Marchantia); asexual by fragmentation or gemmae (green, multicellular buds in gemma cups); sporophyte of foot, seta and capsule.

3.2.2 Mosses — gametophyte has two stages: protonema (creeping, green, branched, filamentous, from spore) and leafy stage (from secondary protonema as lateral bud; upright axes with spirally arranged leaves; multicellular branched rhizoids; bears sex organs). Vegetative reproduction by fragmentation and budding in secondary protonema. Sporophyte more elaborate than in liverworts; elaborate spore-dispersal mechanism. Examples: Funaria, Polytrichum, Sphagnum.

3.3 Pteridophytes

Horsetails and ferns; medicinal, soil-binders, ornamentals.

First terrestrial plants with vascular tissues — xylem and phloem.

Main plant body is the sporophyte with true root, stem and leaves. Leaves: microphylls (Selaginella) or macrophylls (ferns).

Sporangia subtended by sporophylls; compact strobili/cones in Selaginella, Equisetum. Spores by meiosis → free-living, photosynthetic, thalloid gametophyte = prothallus (needs cool, damp, shady places). Water needed for antherozoids to reach the archegonium.

Homosporous (majority, similar spores) vs heterosporous (Selaginella, Salvinia — megaspores and microspores). In heterosporous forms the female gametophyte is retained on the sporophyte and the embryo develops within it — a precursor to the seed habit.

Four classes: Psilopsida (Psilotum), Lycopsida (Selaginella, Lycopodium), Sphenopsida (Equisetum), Pteropsida (Dryopteris, Pteris, Adiantum).

3.4 Gymnosperms

gymnos = naked, sperma = seed — ovules not enclosed by an ovary wall; seeds naked.

Medium or tall trees and shrubs; Sequoia (giant redwood) is one of the tallest trees.

Roots: tap roots; mycorrhiza in Pinus; coralloid roots with N₂-fixing cyanobacteria in Cycas.

Stem unbranched (Cycas) or branched (Pinus, Cedrus); Cycas pinnate leaves persist for a few years; conifers have needle-like leaves, thick cuticle and sunken stomata to reduce water loss.

Heterosporous: microsporangiate (male) strobili → microspores → reduced male gametophyte = pollen grain; macrosporangiate (female) strobili with ovules. Male and female cones on the same tree in Pinus; on different trees in Cycas.

Megaspore mother cell (from nucellus) → four megaspores → one develops into multicellular female gametophyte with two or more archegonia, retained within the megasporangium.

Gametophytes are not free-living. Pollen carried by air → pollen tube carries male gametes to archegonia → zygote → embryo; ovules → seeds (not covered).

3.5 Angiosperms

Flowering plants: pollen grains and ovules develop in flowers; seeds enclosed in fruits.

Size from the smallest *Wolffia* to tall *Eucalyptus* (over 100 metres).

Two classes: dicotyledons and monocotyledons.

Diagrams to Know

Figure 3.1 — algae: Volvox, Ulothrix (green); Laminaria, Fucus, Dictyota (brown); Porphyra, Polysiphonia (red).

Figure 3.2 — Marchantia female and male thalli (archegoniophore, antheridiophore, gemma cup, rhizoids); Funaria gametophyte with sporophyte (capsule, seta); Sphagnum.

Figure 3.3 — Selaginella, Equisetum (strobilus, node, internode), fern (rhizome), Salvinia.

Figure 3.4 — Cycas, Pinus (long and dwarf shoots), Ginkgo.

Key-Facts Sheet

Bentham & Hooker — natural system for flowering plants.

Green: starch; Brown: mannitol/laminarin; Red: floridean starch.

Bryophytes — dominant gametophyte; Pteridophytes — dominant sporophyte, first vascular plants.

Heterospory — Selaginella, Salvinia; precursor of seed habit.

Cycas — coralloid roots; Pinus — mycorrhiza.

Exam Focus

Q: What is the basis of classification of algae? Outline: major pigments, stored food, cell wall composition, number and position of flagella, habitat → Chlorophyceae, Phaeophyceae, Rhodophyceae.

Q: What is heterospory? Significance with two examples. Outline: production of two kinds of spores (micro and mega); female gametophyte retained on sporophyte; embryo develops inside → precursor to seed habit; Selaginella, Salvinia.

Q: Both gymnosperms and angiosperms bear seeds — why classified separately? Outline: gymnosperm ovules/seeds are naked; angiosperm ovules are in an ovary, seeds enclosed in fruit, and they bear flowers.

Match: Chlamydomonas–algae, Cycas–gymnosperm, Selaginella–pteridophyte, Sphagnum–moss.

Key Terms

Thallus (सुकाय)

Isogamy (समयुग्मकता)

Oogamy (विषमयुग्मकता / अण्डयुग्मकता)

Pyrenoid (पाइरीनॉइड)

Holdfast (स्थापनांग)

Gametophyte (युग्मकोद्भिद्)

Sporophyte (बीजाणुउद्भिद्)

Antheridium (पुंधानी)

Archegonium (स्त्रीधानी)

Protonema (प्रथम तंतु)

Gemma (जेमा / मुकुलिका)

Prothallus (प्रोथैलस / पूर्वसुकाय)

Heterospory (विषमबीजाणुता)

Strobilus (शंकु)

Sporophyll (बीजाणुपर्ण)

Common Mistakes

Calling cyanobacteria algae in Plantae — they belong to Monera.

Saying the bryophyte sporophyte is free-living — it depends on the gametophyte.

Mixing up which group has the dominant gametophyte (bryophytes) versus dominant sporophyte (pteridophytes onwards).

Writing that red algae have flagellated gametes — flagella are absent in Rhodophyceae.

Saying Cycas has male and female cones on the same tree — that is Pinus.

💡 Key Learning Points

✓Classification systems evolved from artificial (Linnaeus) to natural (Bentham & Hooker) to phylogenetic, aided by numerical taxonomy, cytotaxonomy and chemotaxonomy.
✓Algae are grouped into Chlorophyceae, Phaeophyceae and Rhodophyceae by pigments, stored food, cell wall, flagella and habitat.
✓Bryophytes (liverworts and mosses) have a dominant haploid gametophyte and a dependent sporophyte; they need water for fertilisation.
✓Pteridophytes are the first vascular plants with a dominant sporophyte; heterospory in Selaginella and Salvinia is a precursor of the seed habit.
✓Gymnosperms bear naked ovules and seeds, while angiosperms bear flowers and enclose seeds in fruits.

👨‍🏫 Teaching Tips

→Bring real specimens where possible: Spirogyra from a pond, moss from a wall, a fern leaf with sori, a pine cone.
→Turn Table 3.1 into a comparison chart students complete for green, brown and red algae.
→Draw a 'dominant generation' diagram across bryophytes, pteridophytes, gymnosperms and angiosperms to show the shift from gametophyte to sporophyte.
→Use the book's ploidy question (protonema, prothallus, zygote of fern, etc.) as a quick board quiz.
→Show agar plates or jelly to connect agar from Gelidium and Gracilaria to daily life.
→Discuss why Sphagnum peat is used for packing living material (water-holding capacity).
→Ask students to explain why heterospory is called a precursor to the seed habit.

📋 Assessment Questions

Can the student classify algae into three classes with pigment, stored food and flagella details?
Can the student describe the life cycle of a moss or liverwort and state where meiosis occurs?
Can the student explain heterospory and give examples?
Can the student differentiate gymnosperms from angiosperms and homosporous from heterosporous pteridophytes?
Can the student match representative genera to their plant groups?

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