bio201- Chapter 30

Overview of Plant Diversity

• Lecture Presentations by Nicole Tunbridge and Kathleen Fitzpatrick

• Focus on Chapter 30: Plant Diversity II: The Evolution of Seed Plants

Adaptations of Seed Plants

• Key Adaptations for Biodiversity

  • Reduced male and female gametophytes enable reproductive efficiency.

  • Gymnosperms: Gametophytes develop within cones.

  • Angiosperms: Gametophytes develop within flowers.

• Seed Structure

  • A seed consists of:

    • Embryo

    • Seed coat (protects embryo)

    • Food supply (nourishes embryo)

• Seed Dispersal

  • Seeds can disperse over long distances (e.g., wind, animals).

  • Example: Fireweed seeds reached Mount St. Helens post-eruption.

Key Concept 30.1: Seeds and Pollen Adaptations

• Evolutionary Adaptations: In addition to seeds, adaptations include:

  • Reduced gametophytes

  • Heterospory (producing two types of spores)

  • Ovules and pollen

• Benefits: Water is not needed for fertilization.

Seed Plant Life Cycles

• Life cycles dominated by sporophyte stage:

  • Gametophytes are microscopic and dependent on the sporophyte.

  • Nutrient supply comes from the parent sporophyte, enhancing survivability.

Heterospory in Seed Plants

• Homosporous vs. Heterosporous

  • Homosporous plants produce one type of spore (bisexual gametophyte).

  • Heterosporous plants produce two types:

    • Megaspores (female gametophytes)

    • Microspores (male gametophytes)

• Sporangia and Sporophylls

  • Spores develop in specialized structures (sporophylls).

  • Megasporophylls produce megasporangia for female gametophytes.

  • Microsporophylls produce microsporangia for male gametophytes.

Structure and Function of Ovules

• An ovule consists of:

  • Megaspore within megasporangium

  • Surrounded by protective integuments (one in gymnosperms, typically two in angiosperms).

Pollen and Sperm Development

• Microspores form pollen grains (male gametophytes) within pollen walls.

• Pollination: Transfer of pollen to seed plant ovules by wind or animals.

• Germination Process: When pollen reaches the female reproductive structure, it forms a pollen tube that discharges sperm.

Seed Development

• Upon fertilization, the zygote develops into a sporophyte embryo, and the ovule matures into a seed.

• Seeds offer evolutionary advantages:

  • Multicellular structure vs. single-cell spores

  • Ability to remain dormant until conditions are optimal.

  • Nutrient reserves for developing seedlings.

Gymnosperms vs. Angiosperms

• Gymnosperms

  • Known for "naked seeds" on sporophylls, typically cones (e.g., conifers).

• Reproductive Adaptations

  • Key adaptations include:

    • Miniaturization of gametophytes

    • Increased survival and dispersal of seeds.

Evolution of Seed Plants

• Early seed plants emerged in the late Devonian period.

• Gymnosperms predominated terrestrial ecosystems during the Mesozoic era.

Diversity of Gymnosperms

• Four Gymnosperm Phyla:

  • Cycadophyta: Flagellated sperm, endangered species.

  • Ginkgophyta: Only Ginkgo biloba exists, known for pollution tolerance.

  • Gnetophyta: Includes Gnetum, Ephedra, and Welwitschia (desert species).

  • Coniferophyta: Largest phylum with diverse species adapting to various climates.

Angiosperms: Diversity and Adaptations

• Angiosperms: Most abundant plants, with over 290,000 species in Phylum Anthophyta.

• Key adaptations include:

  • Flowers and fruits for reproduction and dispersal.

Flower Structure and Function

• Flowers consist of up to four types of modified leaves:

  • Sepals: Protect flower buds.

  • Petals: Attract pollinators.

  • Stamens: Male structures producing pollen.

  • Carpels: Female structures containing ovary and ovules.

Fruit Development and Seed Dispersal

• As seeds mature, fruits develop, providing protection and aiding dispersal.

• Variations of fruits:

  • Fleshy Fruits: (e.g., tomatoes)

  • Dry Fruits: (e.g., nuts, grains)

Angiosperm Life Cycle

• Double fertilization occurs:

  • One sperm fertilizes the egg; the other forms triploid endosperm for nourishment.

Ecological Importance of Seed Plants

• Seed plants are crucial for food, fuel, construction, and medicine.

• Human reliance on seed plants necessitates the preservation of plant diversity.

Threats to Plant Diversity

• Major threats include habitat destruction, leading to extensive loss of species.

• The loss of plants also affects associated animal populations and ecosystems.

Definitions/Descriptions

a. Angiosperm: Flowering plants that produce seeds enclosed within a fruit; largest group of plants with over 290,000 species.

b. Anther: The part of the stamen that produces and contains pollen, essential for reproduction.

c. Carpel: The female reproductive part of a flower, comprising the ovary, style, and stigma.

d. Coniferophyta: A phylum of gymnosperms known for producing cones and needle-like leaves, including pines and spruces.

e. Cycadophyta: An ancient group of gymnosperms with tropical and subtropical distribution, known for their large, fern-like leaves and flagellated sperm.

f. Ephedra: A genus within Gnetophyta, often found in arid regions, known for its medicinal properties, especially ephedrine.

g. Filament: The stalk of the stamen that supports the anther, playing a key role in pollen dispersion.

h. Flower: A reproductive structure composed of various parts, including sepals, petals, stamens, and carpels, designed for sexual reproduction.

i. Fruit: The mature ovary of a flower containing seeds, which aids in their dispersal.

j. Gametophyte: The haploid phase in the plant life cycle that produces gametes; typically microscopic in seed plants.

k. Ginkgophyta: A phylum consisting of only one extant species, Ginkgo biloba, known for its unique fan-shaped leaves and pollution tolerance.

l. Gnetophyta: A diverse group of plants adapted to arid conditions, characterized by unique features like vessels in their xylem.

m. Gnetum: A genus in Gnetophyta known for its broad leaves and primarily tropical distribution.

n. Gymnosperm: Seed plants with unprotected seeds, including conifers and cycads, characterized by their adaptations to diverse environments.

o. Integument: The protective layer surrounding the ovule, usually one in gymnosperms and two in angiosperms.

p. Megasporangia: Structures that produce megaspores, which develop into female gametophytes.

q. Megaspore: A large spore that develops into a female gametophyte within gymnosperms and angiosperms.

r. Microsporangia: Structures responsible for producing microspores, which develop into male gametophytes (pollen grains).

s. Microspore: A small spore that develops into a male gametophyte in seed plants.

t. Ovary: The swollen base of the carpel containing ovules, which later develop into seeds after fertilization.

u. Ovule: The structure containing the female gamete, which will develop into a seed upon fertilization.

v. Petal: The colorful part of a flower that attracts pollinators; part of the corolla.

w. Pollen: The male gametophyte of seed plants, consisting of pollen grains, important for fertilization.

x. Pollination: The transfer of pollen from an anther to a stigma, crucial for fertilization in flowering plants.

y. Seed: A mature ovule containing an embryo, nutrient reserves, and a protective coat; essential for reproduction.

z. Sepal: The outer part of the flower that protects the developing bud and supports the flower structure.

aa. Sporophyte: The diploid, spore-producing phase in the plant life cycle, typically larger and dominant in seed plants.

bb. Stamen: The male reproductive structure of a flower, comprising an anther and filament.

cc. Stigma: The receptive tip of the carpel where pollen grains land and germinate.

dd. Style: The elongated part of the carpel connecting the stigma to the ovary.

ee. Welwitschia: A unique desert plant within Gnetophyta known for its longevity and distinct growth habit.