Chapter 3: Plant Kingdom - Overview
1. Introduction and Classification Systems
Whittaker’s Five Kingdom system (1969) moved fungi and certain prokaryotic/eukaryotic organisms with cell walls out of the Plant Kingdom. Three main types of classification systems have been used over time:
- Artificial Systems: Based on superficial morphological characters like habit, color, and leaf shape (e.g., Linnaeus’s system).
- Natural Systems: Based on natural affinities and internal features like anatomy, embryology, and phytochemistry (e.g., Bentham and Hooker’s system).
- Phylogenetic Systems: Based on evolutionary relationships and common ancestry.
Modern Taxonomic Aids: Numerical Taxonomy (using computers), Cytotaxonomy (chromosomal info), and Chemotaxonomy (chemical constituents).
2. Algae (Section 3.1)
Algae are simple, thalloid, autotrophic, and largely aquatic organisms. They reproduce vegetatively (fragmentation), asexually (zoospores), and sexually (isogamous, anisogamous, or oogamous).
Economic Importance
Responsible for half of the earth’s CO2 fixation, primary producers, food source (e.g., Porphyra, Laminaria), hydrocolloids (algin, carrageen), agar source, and protein supplements (e.g., Chlorella).
- Chlorophyceae (Green Algae): Contain chlorophyll a and b; have pyrenoids for storage; cell walls of cellulose and pectose (e.g., Volvox, Ulothrix).
- Phaeophyceae (Brown Algae): Mostly marine; contain chlorophyll a, c, and fucoxanthin; store food as laminarin or mannitol (e.g., Laminaria, Fucus).
- Rhodophyceae (Red Algae): Mostly marine; contain r-phycoerythrin; store food as floridean starch (e.g., Polysiphonia, Porphyra).
3. Bryophytes (Section 3.2)
Known as the "amphibians of the plant kingdom" because they live in soil but require water for sexual reproduction. The dominant phase is the haploid gametophyte.
- Liverworts: Thalloid plant body (e.g., Marchantia); reproduce asexually via gemmae.
- Mosses: Life cycle involves protonema and leafy stages (e.g., Funaria, Sphagnum).
Importance: Ecological succession on bare rocks; Sphagnum provides peat used as fuel.
4. Pteridophytes (Section 3.3)
Includes horsetails and ferns. They are the first terrestrial plants to possess vascular tissues (xylem and phloem). The dominant phase is the sporophyte.
- Reproduction: Produce spores in sporangia. Gametophytes are small and called prothallus.
- Spore Types: Most are homosporous, but some (e.g., Selaginella, Salvinia) are heterosporous (producing macro and microspores), a precursor to the seed habit.
5. Gymnosperms (Section 3.4)
Plants where ovules are not enclosed by an ovary wall and remain exposed ("naked seeds"). They include medium to tall trees (e.g., Sequoia).
- Roots: Often have fungal associations (mycorrhiza in Pinus) or N2-fixing cyanobacteria (coralloid roots in Cycas).
- Reproduction: Heterosporous; produce male and female cones. Pollen is carried by air currents.
6. Angiosperms (Section 3.5)
The "flowering plants" where seeds are enclosed within fruits. Range from microscopic Wolffia to tall Eucalyptus trees.
- Dicotyledons: Two cotyledons in seeds.
- Monocotyledons: Single cotyledon in seeds.
7. Summary and Exercises
The chapter details life cycles and compares algae classes. The exercises focus on classification bases, economic importance, and terminology.
Key Chapter Concepts
- Classification Basis: Evolution from artificial to phylogenetic systems.
- Algae: Classified by pigments and stored food.
- Life Cycles: Shift from gametophyte dominant (Bryophytes) to sporophyte dominant (Gymnosperms/Angiosperms).
- Evolutionary Milestones: Vascular tissue (Pteridophytes) and Seed habit (Gymnosperms).