Board exam focus — Plant Kingdom (CBSE & HBSE)

This chapter surveys Kingdom Plantae in detail — from the simple algae through bryophytes, pteridophytes and gymnosperms to the advanced angiosperms. It explains the classification, characteristic features and life cycles of each group, and introduces alternation of generations and the three plant life-cycle patterns: haplontic, diplontic and haplo-diplontic.

Algae and Bryophytes

Algae

• Chlorophyll-bearing, simple, thalloid, autotrophic, largely aquatic organisms.
• Body is not differentiated into root, stem and leaves (thallus).
• Reproduction: Vegetative (fragmentation), Asexual (zoospores), Sexual (isogamous/anisogamous/oogamous).

Classification of Algae:

NEET Trap: The red colour of Rhodophyceae is due to r-phycoerythrin; they are found at the greatest ocean depths because red pigment absorbs available blue light. Agar (used in culture media and ice creams) comes from Gelidium and Gracilaria.

Economic importance: Algae fix about half of the total carbon dioxide on earth by photosynthesis (primary producers). Porphyra, Laminaria, Sargassum are used as food; algin (brown algae) and carrageenan (red algae) are commercial products.

Bryophytes — 'Amphibians of the Plant Kingdom'

• Can live in soil but need water for sexual reproduction (hence amphibians).
• The plant body is thallus-like (gametophyte is the dominant, photosynthetic, free-living stage).
• No true roots, stem or leaves — have rhizoids, and root/stem/leaf-like structures.
• No vascular tissue (xylem/phloem absent).

Main male sex organ = antheridium (produces antherozoids); female sex organ = archegonium (flask-shaped, produces egg). Water carries the antherozoids to the egg → fertilisation → zygote → sporophyte. The sporophyte is dependent on the gametophyte.

Importance: Mosses (Sphagnum) provide peat (fuel) and are used in packing; they form dense mats preventing soil erosion; pioneers in plant succession on bare rocks.

Pteridophytes and Gymnosperms

Pteridophytes — First Vascular Plants

• First terrestrial plants to possess vascular tissues (xylem and phloem).
• Plant body differentiated into true root, stem and leaves.
• The dominant phase is the sporophyte (diploid, the main plant body).
• Leaves may be small (microphylls) or large (macrophylls).
• Sporophylls bear sporangia which produce spores by meiosis.

Life cycle: Sporophyte (dominant) → spores → prothallus (gametophyte) → antheridia & archegonia → water needed for fertilisation → zygote → new sporophyte.

Homospory vs Heterospory:

• Most pteridophytes produce similar spores = homosporous.
• Selaginella and Salvinia produce two kinds of spores (large megaspores + small microspores) = heterosporous — a precursor to the seed habit.

Trap: Heterospory in Selaginella is significant because it is the beginning of the seed habit (precursor to seed-bearing plants).

Gymnosperms — Naked-Seeded Plants

• Gymnos = naked, sperma = seeds; ovules are not enclosed by an ovary wall, so seeds are naked.
• Plants are usually trees or shrubs (e.g., giant redwood Sequoia).
• Roots have symbiotic associations: mycorrhiza (in Pinus) and coralloid roots with cyanobacteria (in Cycas).
• Heterosporous — produce haploid microspores and megaspores.
• Male and female gametophytes are highly reduced and retained within the sporangia on the sporophyte.

Cones: Microsporophylls and megasporophylls are aggregated to form male and female cones (strobili).

• No water needed for fertilisation (pollination by wind/air directly to the ovule).

NEET Trap: Cycas has coralloid roots containing N₂-fixing cyanobacteria (Anabaena). Gymnosperms bear naked seeds (no fruit), unlike angiosperms.

Angiosperms and Plant Life Cycle Patterns

Angiosperms — Flowering Plants

• Angio = covered, sperma = seed; seeds are enclosed inside fruits (developed from ovary).
• Range from tiny Wolffia to tall Eucalyptus.
• Bear flowers (reproductive structures); exhibit double fertilisation and triple fusion (unique to angiosperms).

Classification — Two Classes:

Double fertilisation: One male gamete fuses with the egg (syngamy → zygote, 2n); the second male gamete fuses with the two polar nuclei (triple fusion → PEN → endosperm, 3n). This is unique to angiosperms.

Alternation of Generations

In plants, the diploid sporophyte (2n) and haploid gametophyte (n) generations alternate. The sporophyte produces haploid spores by meiosis; spores develop into gametophytes which produce gametes that fuse (fertilisation) to restore the sporophyte.

Plant Life Cycle Patterns

Key trend: Moving up the plant kingdom (algae → angiosperms), the gametophyte progressively reduces and the sporophyte becomes dominant and independent.

NEET Trap: In bryophytes the dominant phase is the gametophyte (haploid), whereas in pteridophytes and all seed plants the dominant phase is the sporophyte (diploid). Both bryophytes and pteridophytes are haplo-diplontic, but they differ in which phase dominates.

Frequently asked questions

Are these Plant Kingdom notes free?

Yes — the Plant Kingdom notes for Biology (Class 11) on Siksha Sarovar are completely free to read, with no account required.

Do these notes follow CBSE and HBSE?

Yes. The Plant Kingdom notes are NCERT-aligned and include guidance for both CBSE and Haryana Board (HBSE), with important questions and MCQs for revision.

What does the Plant Kingdom chapter cover?

Concept explanations, key formulas and definitions, fully solved examples and board-pattern practice questions for Plant Kingdom.