Chapter 3: Plant Kingdom Notes

 

Chapter 3: Plant Kingdom

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Introduction

• Classification of Kingdom Plantae:
  • Kingdom Plantae includes all eukaryotic chlorophyll-containing organisms commonly known as plants.
  • Primarily, they are autotrophic and use photosynthesis to obtain energy.
  • They exhibit alternation of generations with distinct gametophytic and sporophytic stages.

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Classification Systems

• Artificial Classification System:
  • Based on superficial, morphological characteristics like habit, color, and number of leaves.
  • Example: Linnaeus's classification.
• Natural Classification System:
  • Considers natural affinities and includes various internal features like anatomy, embryology, and phytochemistry.
  • Example: Bentham and Hooker’s classification of flowering plants.
• Phylogenetic Classification System:
  • Based on evolutionary relationships, aiming to classify plants based on common ancestry.
  • Modern classifications use phylogenetic data from multiple sources, including cytotaxonomy (cell features), chemotaxonomy (chemical features), and numerical taxonomy.

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Algae

• Characteristics:
  • Algae are simple, chlorophyll-bearing, thalloid, and autotrophic organisms.
  • They are mostly aquatic, found in both freshwater and marine environments, but also inhabit moist soils, stones, and wood.
  • Algae can exist symbiotically with fungi (forming lichens) or animals (e.g., on the shells of sloths).
• Reproduction:
  • Vegetative Reproduction: By simple fragmentation.
  • Asexual Reproduction: By the production of various types of spores, such as zoospores (flagellated, motile spores).
  • Sexual Reproduction: Involves the fusion of gametes, which may be isogamous (similar in size and shape), anisogamous (dissimilar in size), or oogamous (large, non-motile egg and small, motile sperm).
• Economic Importance:
  • Algae are vital as primary producers in aquatic ecosystems.
  • They contribute significantly to carbon dioxide fixation through photosynthesis.
  • Some algae like Porphyra and Laminaria are used as food.
  • Algae like Gelidium and Gracilaria are used commercially to produce agar, while others are used to extract algin (from brown algae) and carrageen (from red algae).
• Classes of Algae:
  • Chlorophyceae (Green Algae):
    • Characteristics: Green in color due to chlorophyll a and b, cell walls made of cellulose, store food as starch.
    • Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara.
  • Phaeophyceae (Brown Algae):
    • Characteristics: Olive green to brown due to the presence of the pigment fucoxanthin. They store food as laminarin and mannitol.
    • Structures: They have a holdfast, stipe, and frond (leaf-like structure).
    • Examples: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus.
  • Rhodophyceae (Red Algae):
    • Characteristics: Red due to the pigment r-phycoerythrin. They store food as floridean starch.
    • Most red algae are marine, thriving in warmer climates.
    • Examples: Polysiphonia, Porphyra, Gracilaria, Gelidium.

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Bryophytes

• General Characteristics:
  • Commonly referred to as "amphibians of the plant kingdom" because they need water to complete their life cycle, particularly for fertilization.
  • Typically found in moist, shady environments.
  • Bryophytes play a role in plant succession, particularly in forming soil in barren regions.
• Plant Body:
  • The dominant phase in their life cycle is the gametophyte, which is haploid and produces gametes.
  • Bryophytes do not have true roots, stems, or leaves but have root-like, stem-like, and leaf-like structures.
• Reproduction:
  • Vegetative Reproduction: Occurs via fragmentation.
  • Sexual Reproduction:
    • Antheridia (male sex organs) produce biflagellate antherozoids.
    • Archegonia (female sex organs) produce a single egg.
    • Fertilization occurs in the presence of water, leading to the formation of a diploid zygote.
    • The zygote develops into a sporophyte, which remains attached to and dependent on the gametophyte.
    • The sporophyte produces haploid spores by meiosis, which germinate to form new gametophytes.
• Classification of Bryophytes:
  • Liverworts:
    • Usually thalloid (body is a flattened structure), they grow in moist, shady areas.
    • Asexual reproduction occurs via the production of gemmae in gemma cups.
    • Example: Marchantia.
  • Mosses:
    • Exhibit two stages: a protonema stage and a leafy stage.
    • The protonema develops directly from spores and gives rise to the leafy gametophyte.
    • Example: Funaria, Polytrichum, Sphagnum.
• Economic Importance:
  • Bryophytes like Sphagnum (peat moss) are used as fuel and in horticulture as a packing material.
  • They are important ecologically, contributing to soil formation and preventing soil erosion.

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Pteridophytes

• General Characteristics:
  • Pteridophytes are the first group of plants to have a well-differentiated vascular system, including xylem and phloem.
  • They are primarily terrestrial and prefer cool, damp, shady places.
  • They are also found in some sandy soils.
• Plant Body:
  • The dominant phase is the sporophyte, which is diploid and is differentiated into true roots, stem, and leaves.
  • Leaves may be small (microphylls) as in Selaginella or large (macrophylls) as in ferns.
• Reproduction:
  • Vegetative Reproduction: Occurs through fragmentation.
  • Sexual Reproduction:
    • The sporophyte produces spores that germinate into a small, multicellular, photosynthetic gametophyte called a prothallus.
    • The gametophyte bears male (antheridia) and female (archegonia) sex organs.
    • Water is essential for fertilization, where antherozoids reach the archegonium and fertilize the egg.
    • The zygote develops into a sporophyte, marking the completion of the life cycle.
• Classification of Pteridophytes:
  • Psilotopsida: Simplest, often considered primitive. Example: Psilotum.
  • Lycopsida: Include club mosses. Example: Selaginella, Lycopodium.
  • Sphenopsida: Include horsetails. Example: Equisetum.
  • Pteropsida: Include true ferns. Example: Dryopteris, Pteris, Adiantum.
• Significance:
  • Some pteridophytes are used for medicinal purposes, as soil-binders, and as ornamental plants.
  • They are important in evolutionary studies as they represent a transition from bryophytes to seed-bearing plants.

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Gymnosperms

• General Characteristics:
  • Gymnosperms are seed-producing plants where seeds are not enclosed within a fruit, hence called "naked seeds."
  • They are typically woody, perennial, and evergreen.
  • They are found in various habitats, including temperate forests and cold regions.
• Reproductive Structures:
  • Sporophyte is the dominant phase and is differentiated into roots, stem, and leaves.
  • Leaves are usually needle-like or scale-like and are adapted to withstand environmental extremes.
  • Gymnosperms bear male and female cones (strobili), with microsporangia and megasporangia, respectively.
• Reproduction:
  • Male Cones produce microspores (pollen grains) that are carried by wind to the female cones.
  • Female Cones produce megaspores, which develop into female gametophytes that remain enclosed within the megasporangium.
  • Pollination is usually anemophilous (wind-pollinated).
  • Fertilization results in the formation of a seed, which develops without a fruit.
• Economic Importance:
  • Gymnosperms are important sources of wood (timber) and non-wood products like resin (from Pinus), turpentine, and varnish.
  • Some, like Ephedra, are used medicinally.

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Angiosperms

• General Characteristics:
  • Angiosperms are flowering plants, the most diverse and widespread group within Kingdom Plantae.
  • They produce seeds enclosed within fruits, a characteristic feature distinguishing them from gym