Plant Evolution and Characteristics Quiz

Plant Evolution and Characteristics

• Plants evolved from green algae, specifically charophytes
• The terrestrial surface was lifeless for 3 billion years
• Plants have diversified into roughly 300,000 living species
• Plants are the primary producers in most terrestrial ecosystems
• Plants supply oxygen and are the ultimate food source for land animals

Derived Traits of Plants

• Embryophytes have four key traits absent in charophytes: -Alternation of generations (with multicellular, dependent embryos) -Walled spores produced in sporangia -Multicellular gametangia -Apical meristems
• Many plants have cuticles and mycorrhizae

Alternation of Generations

• Plants alternate between two multicellular stages:
  • Sporophyte (diploid)
  • Gametophyte (haploid)
• The gametophyte produces haploid gametes by mitosis
• Fusion of the gametes produces the diploid sporophyte
• The sporophyte produces haploid spores by meiosis

Walled Spores Produced in Sporangia

• Sporophytes produce spores in organs called sporangia
• Diploid cells called sporocytes undergo meiosis to produce haploid spores
• Spore walls contain sporopollenin, making spores resistant to harsh environments

Multicellular Gametangia

• Gametes are produced within organs called gametangia
• Female gametangia (archegonia) produce eggs and are the site of fertilization
• Male gametangia (antheridia) produce sperm

Apical Meristems

• Plants sustain continual growth in apical meristems (shoot and root tips)
• Cells from apical meristems differentiate into various tissues

Nonvascular Plants

• Bryophytes are represented by three phyla of small, herbaceous plants: -Liverworts (phylum Hepatophyta) -Hornworts (phylum Anthocerotophyta) -Mosses (phylum Bryophyta)
• Mosses are closely related to vascular plants
• These plants are dominant over a haploid/gametophyte stage throughout their life cycle

Vascular Plants

• Fossils of vascular plants date back about 420 million years
• Early vascular plants had independent, branching sporophytes
• Living vascular plants are characterized by: -Dominant sporophytes -Vascular tissues (xylem and phloem) -Well-developed roots to absorb nutrients and leaves for photosynthesis
• Two phyla of seedless vascular plants: -Lycophytes (e.g., club mosses, spike mosses, quillworts) -Pterophytes (e.g., ferns, horsetails, whisk ferns)
• These plants thrived at great heights during the Carboniferous period

Significance of Seedless Vascular Plants

• Ancient lycophytes and pterophytes proliferated and formed the first forests during the Devonian and Carboniferous periods
• Increased photosynthesis may have helped produce the global cooling at the end of the Carboniferous period
• Decaying plants from these Carboniferous forests became coal

Seed Plants

• Seeds changed the course of plant evolution, enabling them to become dominant producers
• A seed consists of an embryo and nutrients surrounded by a protective coat
• Seeds came about 360 million years before gymnosperms and 200 million years before angiosperms

Seeds and Pollen Grains

• In addition to seeds, all seed plants share the following derived traits: -Reduced gametophytes -Heterospory (male and female spores) -Ovules -Pollen
• The gametophytes of seed plants develop within the parent sporophyte's tissues

Gymnosperms

• These seed plants have "naked" seeds not enclosed by ovaries
• Gymnosperms appeared early in the fossil record and dominated Mesozoic ecosystems
• Gymnosperms are better suited to drier conditions than nonvascular plants
• Four phyla: -Cycadophyta (cycads) -Ginkgophyta (Ginkgo biloba) -Gnetophyta (Gnetum, Ephedra, Welwitschia) -Coniferophyta (conifers such as pine, fir, and redwood

Angiosperms

• Angiosperms came on the scene 130-150 million years ago
• Angiosperms are seed plants with reproductive structures called flowers and fruits
• They are the most widespread and diverse plants
• Two major groups: monocots and eudicots

Characteristics of Angiosperms

• All angiosperms are classified in the single phylum Anthophyta, derived from the Greek word for "flower"
• Angiosperms have specialized features for successful reproduction, such as flowers, double fertilization, fruits, and pollen

Pollination

• Pollination is the transfer of pollen from an anther to a stigma
• Pollination can occur via wind, water, animals (e.g., bees, moths, butterflies, birds, lizards, or bats)

Angiosperm Life Cycle

• Angiosperms undergo a life cycle featuring a prominent sporophyte generation
• Their life cycle includes the flower, double fertilization, and fruit formation

Fruit Form and Function

• A fruit develops from the ovary
• It protects enclosed seeds and aids in seed dispersal by wind or animals
• Fruits may be classified as dry or fleshy

Fruit Dispersal

• Fruit dispersal mechanisms include wind, water, and animals

Reproduction of Plants

• Plants can reproduce sexually or asexually, or both
• Sexual reproduction results in genetically different offspring
• Asexual reproduction results in clones of genetically identical organisms
• Mechanisms of asexual reproduction include fragmentation, rhizomes, and adventitious shoots

Asexual vs. Sexual Reproduction

• Asexual reproduction is beneficial in stable environments, but clones are vulnerable to extinction in changing environments.
• Sexual reproduction generates genetic variation, important for environmental changes

Additional Notes

• Pando (a clonal aspen grove) is a remarkable example of asexual reproduction
• Some gymnosperms/angiosperms have unique adaptations for reproduction, including specific types of flowers, fruits, and pollination methods