Lab A: Bryophytes and Seedless Vascular Plants

Overview of Plant Classification and Evolution

  • Ancestral Lineages of Plants

    • Protist
    • Land plants
    • Cuticle and stomata
    • Vascular plants
    • Seed plants
    • Pollen and seeds
    • Xylem and phloem
    • Flowering plants
      • Flowers and fruits
      • Angiosperms
      • Gnetophytes
      • Conifers
      • Ginkgos
    • Gymnosperms
      • Cycads
    • Seedless vascular plants
    • True ferns
    • Horsetails
    • Whisk ferns
    • Club mosses
    • Bryophytes
    • Mosses
    • Hornworts
    • Liverworts

  • Lab A: Bryophytes and Seedless Vascular Plants

Origin of Plants

  • Archaeplastida

    • Plants evolved approximately 500 million years ago
    • Land plants share significant traits with certain algal groups
    • Eukaryotic: Characterized by a membrane-enclosed nucleus
    • Multicellular: Organisms consisting of multiple cells.
    • Photosynthetic: Capable of photosynthesis, producing oxygen and organic compounds.
    • Cell Walls: Composed of cellulose, providing structure and rigidity.
    • Chlorophyll a and b: Types of chlorophyll key to the photosynthetic process.

  • Viridiplantae: A clade that includes green plants.

Shared Traits Between Charophytes and Land Plants

  • Modern-day Charophytes may resemble ancestral forms of land plants.
  • Traits shared:
    • Cells have distinctive circular rings of protein embedded in the plasma membrane.
    • Flagellated sperm: Structurally unique, adapted for swimming in water.

Highlights of Plant Evolution

  • Fossil Record identifies four major milestones in plant evolution:
    • Transition to land: Occurred approximately 475 million years ago
    • Development of vascular tissue: Emerged around 425 million years ago
    • Origin of seeds: Recorded at about 350 million years ago
    • Appearance of flowers: Noted approximately 160 million years ago

Terrestrial Adaptations

  • The transition to terrestrial environments introduced challenges related to resource acquisition:
    • Access to Light and CO2 from the air
    • Availability of Water and minerals in soil

Derived Plant Traits

  • Adaptations enhancing survival and reproduction on land include:
    • Spores with durable walls: Allowing resistance to dry conditions
    • Waxy cuticle: Reducing water loss across cell walls
    • Specialized cells: Thickened cell walls providing rigid support
    • Apical meristems: Regions of growth at terminal buds promoting rapid vertical growth

Bryophytes

  • Three clades of seedless plants:

    • No vascular tissue or true leaves
    • Nutrient and water movement through diffusion and osmosis
    • Characterized by low growth and herbaceous (non-woody) nature
    • Rhizoids: Structure serving anchorage but lacking full roots.
    • Photosynthesis occurs primarily in microphylls.
    • Examples:
    • Moss
    • Liverwort
    • Hornwort

  • Terrestrial Adaptations of Bryophytes:

    • Waxy cuticle to prevent dehydration
    • Developing embryos retained by the mother plant
    • Gametophyte dominance: This stage is the most prominent within the lifecycle.

Derived Plant Traits in Vascular Plants

  • Vascular system: Facilitating access to deep soil water and efficient nutrient distribution
    • Xylem: Transports water and minerals throughout the plant
    • Phloem: Responsible for transporting sugars, amino acids, and other organic compounds
  • Cambium: A layer of partially undifferentiated cells aiding in plant growth.

Function and Structure of Leaves

  • Leaves:
    • Enhance the surface area for plant functions
    • Serve as primary photosynthetic organs
    • Gas exchange facilitated through stomata (pores in leaves)

True Roots

  • Roots:

    • Organs specialized in absorbing water and nutrients
    • Provide structural anchorage for the plant
    • Possess apical meristems like stems do
    • Rhizoids vs. True Roots:
    • Rhizoids primarily serve for anchorage without involved nutrient uptake.

  • Advantages of Vascular Tissues, Roots, and Leaves:

    • Enable survival in water-scarce areas
    • More effective at water and nutrient uptake
    • Offer structural advantages due to lignin in cell walls, contributing to height, thickness, and weather resilience.

Seedless Vascular Plants

  • Characterized by the presence of xylem and phloem.
  • Typically feature true roots and leaves.
  • Two clades exist:
    • Monilophytes: Includes ferns, horsetails, and whisk ferns.
    • Ferns represent the most diverse group within this clade.
    • Lycophytes: Comprises club mosses, spike mosses, and quillworts.
    • Examples of specific plants:
      • Horsetail
      • Spike moss
      • True fern
      • Quillwort

Common vs. Scientific Naming of Organisms

  • Common Names:
    • Frequently used but can lead to confusion due to:
    • Multiple common names for a single species
    • Different species sharing the same common name
  • Scientific Names:
    • Each organism has a single scientific designation, facilitating accurate identification.
    • Examples include:
    • Homo sapiens for humans
    • Panthera tigris for tigers
    • Puma concolor: Commonly referred to as cougar, but is also called mountain