Class 11 Biology Plant Kingdom — Samacheer Kalvi Bio Botany Notes

Quick Summary

The Plant Kingdom (Plantae) is classified into five major groups based on complexity, vascular tissue, seeds, and flowers. Understanding the evolutionary progression — algae → bryophytes → pteridophytes → gymnosperms → angiosperms — is the key. Alternation of generations and heterospory are the two conceptual pillars of this chapter.

Overview of Plant Groups

Algae

• Habitat: Aquatic (fresh water and marine), moist soil, bark of trees
• Body: Thallus (no root, stem, leaf differentiation)
• Reproduction: Vegetative (fragmentation), asexual (spores), sexual
• Economic importance: Food (Porphyra, Laminaria), agar (Gelidium), biofuel, O₂ production

Classification by Pigment

Bryophyta — "Amphibians of Plant Kingdom"

• Features: No vascular tissue, no roots (rhizoids), no seeds
• Gametophyte dominant (the green plant you see is the gametophyte)
• Need water for fertilisation (motile antherozoids)
• Divisions: Liverworts (Marchantia), Hornworts (Anthoceros), Mosses (Funaria)
• Importance: Sphagnum moss used as packing material and fuel (peat)

Pteridophyta — First Vascular Land Plants

• Features: Vascular tissue (xylem + phloem), no seeds, spores for reproduction
• Sporophyte dominant
• Examples: Ferns (Nephrolepis), Selaginella, Equisetum, Lycopodium
• Heterospory: Selaginella produces microspores and megaspores → seed habit precursor

Alternation of Generations in Ferns

Sporophyte (2n) → meiosis → spores (n) → gametophyte (prothallus, n) → gametes → zygote → sporophyte (2n)

Gymnosperms — Naked Seed Plants

• Features: Seeds not enclosed in fruit, no flowers, wind pollinated
• Sporophyte dominant; gametophyte reduced
• Examples: Pinus, Cycas (living fossil), Ginkgo, Sequoia (tallest tree)
• Cycas: Dioecious (separate male and female plants); motile sperms (primitive feature)
• Pinus: Monoecious; microsporangia on male cones, megasporangia on female cones

Angiosperms — Flowering Plants

• Features: Seeds enclosed in fruits, flowers for reproduction, most advanced
• Double fertilisation: One sperm + egg → zygote (2n); one sperm + polar nuclei → endosperm (3n)
• Divided into:
• Monocots: One cotyledon, parallel venation, fibrous roots (e.g., rice, wheat, maize)
• Dicots: Two cotyledons, reticulate venation, taproot (e.g., mango, pea, rose)

Alternation of Generations — Summary

Important Questions

One Mark

• Name the pigment responsible for the red colour in Rhodophyceae.
• Why are bryophytes called amphibians of the plant kingdom?
• Name a heterosporous pteridophyte.
• What is double fertilisation?

Short Answer (3 marks)

• Distinguish between gymnosperms and angiosperms with two examples each.
• What is alternation of generations? In which plant group is the gametophyte the dominant phase?
• Compare monocots and dicots on the basis of four characters.

Long Answer (5 marks)

• Describe the classification of algae based on pigments. Give the stored food, flagella type, and one example for each class.
• Explain the life cycle of a fern with a labelled diagram showing alternation of generations.

Common Mistakes

• Thinking bryophytes have vascular tissue — they do NOT (no xylem or phloem).
• Confusing gymnosperms (naked seeds) with angiosperms (enclosed seeds) — "gymno" = naked.
• Double fertilisation: forgetting the endosperm is triploid (3n), not diploid.
• Placing all algae in Plantae — unicellular algae (Chlamydomonas) are in Protista under Whittaker's system.

Board Exam Tips

• The comparison table (vascular tissue, seeds, flowers, dominant phase) for all five groups is a standard 5-mark question.
• Alternation of generations diagram for fern is regularly asked — know both sporophyte and gametophyte stages.
• Monocot vs dicot comparison (4 characters) is a reliable 3-mark question.
• NEET: Plant kingdom classification and examples (Selaginella, Cycas, Pinus features) appear frequently.