Plant Kingdom - Chapter 3 Overview

Classification of Plantae

• Based on Whittaker's Five Kingdom classification: Monera, Protista, Fungi, Animalia, Plantae.
• Historical classifications included fungi, Monera, and Protista with cell walls in Plantae.
• Current classification excludes these, focusing on Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms.

Evolution of Classification Systems

• Early systems (Linnaeus) based on superficial morphology (habit, leaf shape, color).
• Natural systems consider internal features (anatomy, embryology, phytochemistry).
• Bentham and Hooker proposed a natural system for flowering plants.
• Phylogenetic systems focus on evolutionary relationships with common ancestors.
• Modern systems include:
  • Numerical Taxonomy: Uses computers to analyze characteristics.
  • Cytotaxonomy: Focuses on cytological data.
  • Chemotaxonomy: Uses chemical constituents.

3.1 Algae

• Characteristics:
  • Thalloid, autotrophic, mainly aquatic, chlorophyll-bearing.
  • Forms: colonial (Volvox), filamentous (Ulothrix, Spirogyra), large (kelps).
• Reproduction:
  • Vegetative: fragmentation.
  • Asexual: flagellated zoospores.
  • Sexual: isogamous, anisogamous, oogamous.
• Importance:
  • Photosynthesis contributes to carbon fixation and oxygen.
  • Base of aquatic food cycles; used as food and for hydrocolloids production.
• Classes:
  • Chlorophyceae: Green algae.
  • Phaeophyceae: Brown algae, marine.
  • Rhodophyceae: Red algae, marine.

3.2 Bryophytes

• Characteristics:
  • Amphibians of plant kingdom; need water for sexual reproduction.
  • Thallus-like body with rhizoids, no true roots, stems, leaves.
• Reproduction:
  • Haploid gametophyte, antheridia (male) and archegonia (female) organs.
  • Zygote grows into sporophyte, dependent on gametophyte.
• Ecological Role:
  • Soil stability, peat production, pioneer species in colonization.
• Divisions:
  • Liverworts: Thalloid body, asexual gemmae.
  • Mosses: Two-stage life cycle, elaborate sporophyte.

3.3 Pteridophytes

• Characteristics:
  • Vascular tissues (xylem/phloem), true roots, stems, leaves.
• Life Cycle:
  • Dominant sporophyte phase, spore-producing sporangia.
  • Gametophytes are small, require moist environments.
• Significance:
  • Evolutionary step towards seed habit.
• Classes:
  • Psilopsida, Lycopsida, Sphenopsida, Pteropsida.

3.4 Gymnosperms

• Characteristics:
  • Naked seeds, no ovary wall, dominant sporophyte.
  • Includes tap roots, needle-like leaves, adapted to extreme climates.
• Reproduction:
  • Produce microspores and megaspores; pollen transferred by air.
• Examples: Cycas, Pinus, Ginkgo.

3.5 Angiosperms

• Characteristics:
  • Seeds enclosed in fruits, large diversity, occur in various habitats.
• Classes:
  • Dicotyledons and Monocotyledons.
• Importance:
  • Significant for food, fuel, medicine, commercial products.

Summary

• Algae, bryophytes, pteridophytes, gymnosperms, and angiosperms cover the plant kingdom.
• Discusses reproductive strategies, structural characteristics, ecological importance, and evolutionary advancements.