Plant Diversity Review

Plant Diversity

Diversity Review

  • Definition: Abundance and variety in living organisms.

  • Indigenous Species: Species that occur naturally in a particular habitat.

  • Endemic Species: Species that occurs only in a specific habitat and nowhere else in the world.

  • Exotic/Alien Species: Species that does not occur naturally in a habitat and was brought in from another area.

  • Indicator Species: A species that enables ecologists to determine environmental health of an ecosystem. This species can amplify the effects of human activities on an environment, often disrupting food webs and making ecosystems more fragile.

  • Keystone Species: These are species that have an extremely high impact on a particular ecosystem relative to its population.

Plant Diversity Overview

  • Total of 280,000 plant species.

  • Land plants evolved approximately 500 million years ago (mya).

  • Essential needs for plants include: soil, water, nutrients, stability, air, sunlight, and carbon dioxide.

  • Plants have developed various structures such as root systems, leaves, stems, seeds, flowers, and vascular systems.

Classification of Plants

  • Plant Kingdom:

    • Nonvascular Plants

    • Mosses

    • Seedless Vascular Plants

    • Ferns

    • Vascular Plants

    • Seedless (e.g., ferns, horsetails)

    • Seeds

      • No Flowers (Gymnosperms, e.g., pine trees)

      • Flowers (Angiosperms, e.g., roses)

Phylogenetic Trees

  • Definition: A phylogenetic tree describes the evolutionary relationships between different taxa.

  • Key features:

    • Indicates which taxa developed first and which are closely related.

    • Each branch with descendants represents the most recent common ancestor.

Major Taxonomic Groups

  • Bryophytes: Non-vascular plants (e.g., mosses).

  • Pteridophytes: Seedless vascular plants (e.g., ferns).

  • Gymnosperms: Seed-bearing plants, vascular (e.g., conifers).

  • Angiosperms: Flowering plants, characterized by seeds enclosed within fruits.

Characteristics of Plants

  • Contain chlorophyll.

  • Multi-cellular organisms.

  • Possess cellulose cell walls.

  • Have vacuoles filled with cell sap.

  • Contain plastids for photosynthesis and storage.

  • Exhibit both sexual and asexual reproduction.

  • Have complex life cycles involving both gametophyte and sporophyte generations.

Chromosomes in Plants

  • Homologous Chromosomes: Similar in shape and size, carrying similar genes; one set from each parent.

    • In humans: Total chromosomal count = 46 (23 from each parent).

    • Examples of haploid (N) and diploid (2N) numbers:

    • Humans: N = 23; 2N = 46.

    • Dogs: N = 39.

Important Terms

  • Non-Vascular Plants: Lack specialized tissue for transport, rely on diffusion and water for reproduction.

  • Vascular Tissue: Specialized tissue for transport, including xylem (transports water) and phloem (transports food).

  • True Roots and Leaves: Possesses supporting and conducting tissues.

  • Seeds and Spores: Spores are uniform; seeds vary, resulting in greater diversity.

  • Cones and Flowers: Structures where seeds can be found, either in cones (gymnosperms) or flowers (angiosperms).

Bryophyta – Mosses

  • Characteristics:

    • Terrestrial, but not well adapted for land.

    • Small plants with simple structures, evolved from algae approximately 400 mya.

    • Considered pioneer plants, first to colonize new areas.

    • Typically found in damp environments.

    • Possess thin leaves which easily lose water.

    • No true roots, stems, seeds, or flowers (thallus); lack vascular structures, relying on diffusion for transport.

    • Reproduce via tiny spores rather than seeds with sperm requiring water for swimming to egg cells for fertilization.

Ecological Importance of Bryophyta

  • Primary Plant Succession: Mosses trap dust and organic materials which decompose to form soil.

  • Soil Formation: Binds soil, prevents erosion, enriches soil with organic matter.

  • Economic Value: Source of peat from marshlands.

Vascular Plants

  • Xylem: Transports water and is stiffened with lignin, allows one-way flow.

  • Phloem: Transports food (glucose), allowing two-way flow with end walls containing perforations.

Pterophytes – Ferns

  • Evolved from algae about 400 mya.

  • Grow in moist, shady environments; have true stems, roots, and leaves.

  • Leaves possess a waxy cuticle to minimize water loss.

  • Reproduce using spores, released from the underside of leaves; sperm cells require water to reach egg cells.

Importance of Pteridophytes

  • Ecological Role: Participate in plant succession, replacing mosses.

  • Aesthetic Value: Used in gardens and floral arrangements.

  • Medicinal Uses: Consumed as tea, utilized for various medicinal properties.

  • Economic Uses: Tropical tree fern is used as building material.

Fern Life Cycle

  • Involves stages from young sporophyte, through maturation, to fertilization:

    • Sporophyte (2n) undergoes meiosis in sporangium to produce spores.

    • Gametes: Male and female gametophytes develop, producing sperm and egg cells. Fertilization leads to zygote formation.

Seed-Bearing Plants

Gymnosperms - Conifers

  • Largest and oldest plants, dominant during Carboniferous period.

  • Feature cone-bearing structures (e.g., Yellowwood).

  • Exhibit true roots, stems, leaves, complex vascular systems, and thick waxy cuticle to prevent water loss.

  • Male and female cones produce naked ovules that are unprotected.

Reproduction in Gymnosperms

  • Male cones contain pollen sacs and undergo meiosis.

  • Pollination occurs via wind.

Ecological Importance of Gymnosperms

  • Provide wood for paper, timber industry, furniture, and resin.

Angiosperms – Flowering Plants

  • Most advanced, with complex vascular systems and true reproductive organs (flowers).

  • Seeds develop in the ovary; fruits arise from mature ovaries.

  • Habitat variations include mesophytes, hydrophytes, and xerophytes.

Importance of Angiosperms

  • Major agricultural sources (e.g., wheat, rice, maize).

  • Serve as biofuels and building materials.

  • Contribute cultural and aesthetic values, attract tourism, and provide medicinal outputs.

Pollination in Angiosperms

  • Process involves the transfer of pollen from male anther to female stigma.

  • Types:

    • Cross-Pollination: Involves pollen from one plant transferring to a different plant.

    • Self-Pollination: Occurs within the same flower.

Double Fertilization in Angiosperms

  • Unique process where one sperm fertilizes the egg (forming the zygote) and another fertilizes polar nuclei (forming endosperm).

Comparative Study of Major Plant Groups

  • Bryophytes: Non-vascular, no true leaves/roots, spores, water-dependent fertilization.

  • Pteridophytes: Vascular, true leaves/roots, spores, water-dependent fertilization.

  • Gymnosperms: Vascular, true leaves/roots, seeds, water-independent fertilization.

  • Angiosperms: Vascular, true leaves/roots, seeds, water-independent fertilization, seeds enclosed in ovaries.

Summary of Plant Diversity and Adaptations to a Terrestrial Life

  • Bryophytes: Small plants, depend on water for fertilization; reproduce via spores.

  • Pteridophytes: Larger plants with vascular tissue, depend on water for fertilization; reproduce via spores.

  • Gymnosperms: Produce seeds; reproduction independent of water.

  • Angiosperms: Also produce seeds, with reproduction independent of water; develop seeds in ovaries and produce fruits for seed dispersion.

Advantages of Seed Production:

  • Protection: Seeds are encased in a seed coat that protects the embryo from environmental stresses such as desiccation and predation.

  • Dormancy: Seeds can remain dormant for long periods, allowing them to germinate at a more favorable time for growth, which increases survival rates.

  • Nutrient Storage: Seeds contain stored food (endosperm) that nourishes the developing plant embryo during germination, which is crucial for initial growth.

  • Dispersal Mechanism: Seeds can be dispersed by various methods (wind, water, animals), ensuring the spread of the species over various habitats which helps reduce competition among seedlings.

  • Genetic Diversity: Seed production promotes genetic mixing through sexual reproduction, leading to adaptation and resilience in changing environments.

  • Reproductive Advantage: Production of seeds often increases reproductive success compared to other methods like spores, as seeds can have various strategies for longevity and germination.