Unit 3, lecture 7

Plant Kingdom

Learning Objectives

  • Unit Objectives: Discuss the evolution and adaptations of seedless plants, both vascular and non-vascular; Discuss the evolution and adaptations of seed plants.
  • Lecture Objectives:
    • Compare structural, physiological, and reproductive adaptations that allowed plants to survive the transition from water to land.
    • Relate the origin of plants to green algae.
    • Compare the four major periods of plant evolution and the major adaptations associated with each stage.
    • Describe the life cycle and two key terrestrial adaptations of mosses.
    • Compare ferns and mosses.
    • Describe environmental conditions favoring the evolution of gymnosperms and three adaptations that first appeared in gymnosperms for life on land.
    • Describe flower structures and functions, including the adaptive significance of pollinator attraction.

Pre-Lecture Questions

  • Understanding Photosynthesis:
    • Chemical equation summarizing photosynthesis:
    • Correct Equation: Light Energy + $6 CO2 + 6 H2O o C6H{12}O6 + 6 O2$
  • Understanding Haploid and Diploid:
    • If diploid chromosome number of sexually-reproducing species is 58:
    • Correct Statement: The haploid chromosome number is 29.

What is a Plant?

  • A plant is a multicellular eukaryote that carries out photosynthesis and possesses adaptations for living on land.
  • Comparison with Animals and Fungi:
    • Animals and fungi are also eukaryotic and multicellular.
    • Large algae, such as seaweeds, are photosynthetic but classified as protists rather than plants due to a lack of terrestrial adaptations.

Terrestrial Adaptations of Plants

  • Challenges of Living on Land:
    • Upright bodies in buoyant water lose structural support and may shrivel in drying air.
    • Algae cannot obtain atmospheric carbon dioxide for photosynthesis easily, leading to extensive adaptations needed.
    • The transition from water to land took over 100 million years.

Adaptations of the Plant Body

  • Resource Distribution:
    • On land, resources are found in different environments:
    • Carbon dioxide: mainly in the air.
    • Mineral nutrients and water: primarily in the soil.
  • Specialized Organs:
    • Subterranean organs called roots anchor the plant and absorb minerals and water.
    • Above ground, shoots consist of photosynthetic leaves supported by stems.
Photosynthetic Organs
  • Main Photosynthetic Organs: Leaves, utilizing stomata (microscopic pores on leaves) for gas exchange (CO2 and O2).
  • Waxy Cuticle: A protective waxy layer on leaves prevents water loss.
  • Vascular Tissue: A network of tube-shaped cells branches throughout the plant for transport of vital materials between roots and shoots.
Vascular Tissue
  • Types of Vascular Tissue:
    • Xylem: Transports water and minerals from roots to leaves.
    • Phloem: Distributes sugars from leaves to roots and non-photosynthetic parts.
  • Lignin: A chemical that hardens many vascular tissue cell walls, crucial for structural strength and wood formation.

Reproductive Adaptations

  • Requirement of New Reproductive Modes:
    • Water ensures the gametes (sperms and eggs) and developing offspring do not dry out.
    • New adaptation needed for gamete protection and development outside of water.
  • Egg Fertilization:
    • In plants, the egg is fertilized while retained within the mother's body tissue.
    • Zygote develops into an embryo enclosed within protective ovule without dehydrating.

The Origin of Plants

  • Evolutionary History:
    • Algal ancestors of plants flourished on moist edges of water bodies over 500 million years ago.
    • Charophytes: A modern lineage of green algae that resembles early plant ancestors.
    • Adaptations for dry land began accumulating by about 470 million years ago, marked as the age of the oldest plant fossils.

Highlights of Plant Evolution

  • Chronicle of Four Major Periods:
    • 470 Million Years Ago: Early diversification led to Bryophytes, such as mosses, liverworts, and hornworts. These lacked lignified walls, roots, and leaves.
    • 425 Million Years Ago: Evolution of vascular plants with conducting tissues hardened with lignin.
    • 360 Million Years Ago: First seed plants evolved with seeds containing embryos and food supply, notably gymnosperms like conifers.
    • 140 Million Years Ago: Emergence of angiosperms with complex reproductive structures (flowers) enclosing seeds in ovaries.

Bryophytes

  • Moss Adaptations:
    • Key terrestrial adaptations:
    • A waxy cuticle prevents dehydration.
    • Embryo protection within the female gametophyte.
  • Reproduction: Require water for sperm to swim to eggs.
  • Distinct Forms:
    • Gametophyte: The recognizable green spongelike plant.
    • Sporophyte: Grows from gametophyte as a stalk with a capsule.
Life Cycle of Moss
  • Alternation of Generations:
    • Gametophytes produce gametes forming zygotes which develop into sporophytes.
    • Sporophytes produce spores giving rise to new gametophytes.
Moss Life Cycle Components
  • Includes parts such as:
    • Capsule, Seta, Foot, Venter, and Neck canal.
    • Fertilization resulting in meiospores that lead to next generation.

Ferns

  • Diversification through Vascular Tissue:
    • Ferns are diverse seedless vascular plants with over 12,000 species and can colonize various habitats.
    • Require water for sperm mobility similar to mosses.
    • Had a semi-reduced sporophyte generation.
  • Carboniferous Contributions:
    • Ancient ferns contributed to coal formation through dying and accumulating in wetlands.
Impact of Fossil Fuels
  • Fossil fuels (coal, oil, natural gas) are derived from ancient plant remains and contribute to climate change when burned.

Fern Life Cycle

  • Involves stages such as:
    • Diploid sporophyte producing haploid spores through meiosis and subsequent fertilization to form zygotes.

Gymnosperms

  • Adaptation to Dry and Cold Climate:
    • Evolved towards drier climate, enabling completion of life cycles and enduring harsh winters.
    • Descendants include conifers, the cone-bearing groups.
Terrestrial Adaptations of Gymnosperms
  • Three main adaptations compared to ferns:
    1. Significantly more developed sporophyte generation.
    2. Development of pollen for fertilization via wind.
    3. Formation of seeds, consisting of plant embryo and food supply within a protective coat.

Angiosperms

  • Dominance in Modern Landscape:
    • Approximately 250,000 species of angiosperms versus 700 species of gymnosperms.
    • Success is attributed to refined vascular tissues and evolution of flowers for reproductive success.
    • Importance of attracting pollinators through showy flowers vs. wind-adapted smaller flowers.
Angiosperm Life Cycle
  • Flower Structure:
    • Comprised of modified leaves arranged in circles, with outer green sepals, colorful petals, male structures (stamens), and female structures (carpels).
    • Pollen grains develop in anthers and undergo fertilization leading to zygote development.
    • Produced seeds surrounded by nutritious endosperm, capable of dormancy.
Role of Fruit
  • Function of Fruit:
    • Ripened ovary helps protect seeds, enhances dispersal, and provides food for animals.

End of Lecture Review

  • Characteristics of Plants:
    • Correct option is: Multicellular, eukaryotic, and photosynthetic.
  • Closest Relatives to Land Plants:
    • Charophytes.
  • Differences in Bryophytes:
    • Lack vascular tissue and have flagellated sperm.
  • Diploid Generation in Moss Life Cycle:
    • Produces spores and is called the sporophyte.
  • Pine Tree Observation:
    • What you see is a diploid sporophyte.
  • Unique Feature of Angiosperms:
    • Only angiosperms have flowers.
  • Fertilization result of Seed Plants:
    • Develop into seeds.