CHAPTER 25 Seedless Plants

DEFINITIONS

  • Sporophyte: The diploid generation in the alternation of generations in which the plant develops from the fertilized egg (zygote) and produces haploid spores through the process of meiosis. The sporophyte is typically the dominant life stage in vascular plants.

  • Gametophyte: The haploid generation in the alternation of generations that produces gametes (sperm and eggs) through mitosis. In non-vascular plants like bryophytes, the gametophyte stage is the dominant phase of the life cycle.

  • Apical Meristem: A region of actively dividing cells located at the tips of roots and shoots, responsible for primary growth and elongation of plant structures.

ALTERNATION OF GENERATIONS

  • All plants undergo a life cycle characterized by alternating between two distinct generations: the sporophyte (diploid) and the gametophyte (haploid).

  • The cycle includes:

    • Sporophyte undergoes meiosis to produce haploid spores.

    • Spores germinate and develop into gametophytes.

    • Gametophytes produce gametes through mitosis.

    • Fertilization occurs, resulting in a diploid zygote that develops into a new sporophyte.

GENERAL CHARACTERISTICS OF PLANTS

  • Adaptations to assist in a terrestrial lifestyle include:

    • Waxy Cuticle: A protective layer that prevents water loss and desiccation while allowing for some gas exchange.

    • Stomata: Specialized openings on leaves that facilitate gas exchange (CO2 in, O2 out) while regulating water loss.

    • Vascular Tissue: Composed of xylem and phloem, vascular tissues provide structural support, transport water, nutrients, and photosynthetic products throughout the plant.

EVOLUTIONARY CONTEXT

  • The closest non-plant relatives of land plants are the Charophytes, a group of green algae. These organisms share key characteristics with land plants, such as the presence of chlorophyll a & b, and the formation of a phragmoplast during cell division.

BRYOPHYTES

  • Examples include:

    • Hepaticophyta (Liverworts)

    • Anthocerotophyta (Hornworts)

    • Bryophyta (Mosses)

  • General characteristics of this phylum include:

    • Nonvascular structure, dependent on water for reproduction.

    • Dominance of the gametophyte stage in the life cycle, often forming leafy structures and requiring moist habitats.

TERRESTRIAL ADAPTATIONS

  • Roots: Anchor the plant in the soil, absorb water and nutrients, and can engage in symbiotic relationships with fungi for enhanced nutrient uptake.

  • Leaves: Photosynthetic organs that increase the surface area for effective light capture.

  • Xylem: Specialized vascular tissue that transports water and dissolved minerals from roots to the rest of the plant; lignified for structural support.

  • Phloem: The vascular tissue responsible for transporting sugars and nutrients produced in photosynthesis throughout the plant.

This organized structure follows your study guide's request while also providing definitions and characteristics to enhance the understanding of plant biology.