Lecture Ch. 30 ______ Chapter 30 ~ Plant Diversity II: The Evolution of Seed Plants

Seed Plant Reproductive Adaptations Reduction of the gametophyte: shift from haploid to diploid condition; female gametophyte and embryo remain in sporangia (protection against drought and ionizing radiation on land?) Advent of the seed multicellular sporophyte embryo with food supply and protective coat; heterosporous (two types of spores): megaspores--->female gametophyte--->eggs; microspores---> male gametophyte--->sperm Evolution of pollen: develop from microspores which mature into the male gametophytes; resistant and airborne for a terrestrial environment; eliminated water (sporopollenin coats)

Seed Plants P. 598 Reduced gametophyte dependent on sporophyte Gametophyte is surrounded by tissues of sporophyte Gametophyte derives its nutrition from the sporophyte

Seeds - an important means of dispersing offspring Seed consists of a sporophyte embryo packaged along with a food supply and a protective coat. The gametophyte develops within the confines of a spore p.598 (fig. C) Seed plants are heterosporous-means they have two different types of sporangia that produce two types of spores Megasporangia produce megaspores which give rise to female gametophytes Microsporangia produce microspores which give rise to male gametophytes

Ovule to Seed Sporophylls are small reproductive leaves where pollen cones and ovulate cones develop Megasporangium is surrounded by integuments Megaspore develops inside the megasporangium Integuments, megasporangium, megaspore make up the ovule

Fertilized Ovule Female gametophyte develops inside a megaspore and produces one or more egg cells Megaspore develops into multicellular female gametophyte Micropyle the only opening through the integuments-allows entry of a pollen grain Pollen grain contains a male gametophyte which develops a pollen tube that discharges

Gymnosperm Seed Fertilization initiates the transformation of the ovule into a seed, which consists of a sporophyte embryo, a food supply, and a protective seed coat derived from the integuments

Gymnosperms Cone-bearing plants Lack enclosed chambers (ovaries) for seeds Ovules and seeds develop on specialized leaves called sporophylls Ginkgo, cycads, and conifers All are “evergreens” Needle-shaped leaves Vascular tissue refinement: tracheids~ water conducting and supportive element of xylem

Angiosperms Most diverse and geographically widespread of all plants “Flowering plants”(Phy: Anthophyta) Monocots: 1 embryonic seed leaf (lilies, palms, grasses, grain crops) Dicots: 2 embryonic seed leaves (roses, peas, sunflowers, oaks, maples) Vascular tissue refinement: vessel elements/fiber cells

The flower: the defining structure of angiosperms Reproductive structure: pollen transfer; specialized shoot with modified leaves Sepals: enclose flower before it opens Petals: attract pollinators Stamens: male; anther (produces pollen), filament Carpels: female; stigma, style, ovary, ovules

Angiosperm life cycle Fruit (mature ovary); seeds from ovules Pollen grains: 2 haploid cells (immature male gametophytes) Ovules (female gametophyte~ embryo sac) Double fertilization: 1 sperm w/ egg = diploid zygote; other sperm w/ 2 nuclei in center of sac = triploid endosperm