Download Evolution of Seed Plants - Biology for Science - Lecture Notes and more Study notes Biology in PDF only on Docsity! Plant Diversity: Chapt. 30 – The Evolution of Seed Plants Plant Origins [See Fig. 29.7] Seed plants appeared ~360 m.y.a. with the rise of the Gymnosperms Flowering plants (Angiosperms) – the other surviving lineage – appeared ~200 million years later Major clades of plants [See Fig. 30.2] Bryophytes Gametophyte dominant; sporophyte dependent; gametophyte independent Seedless vascular plants Sporophyte dominant; sporophyte initially dependent; gametophyte independent Seed plants Sporophyte dominant; sporophyte independent; gametophyte dependent & microscopic Gymnosperms – Gametophytes develop inside cones Angiosperms – Gametophytes develop inside flowers Gametophytes develop from spores retained within sporangia of the parental sporophyte Heterosporous spore production [See diagram on pg. 586] Seed plant reproduction, illustrated with a pine [See Fig. 30.3] Layers of integuments envelope and protect the megasporangium The whole structure – megasporangium, megaspore, and integuments – is called an ovule A megaspore develops into a multicellular female gametophyte Fertilization initiates the transformation of the ovule into a seed Compared to a single-celled spore, a seed is much more resistant and complex GYMNOSPERMS “Naked seeds”; not enclosed by an ovary and develop on the surface of modified leaves that usually form cones (strobili) Docsity.com Phylum Ginkgophyta Ginkgo biloba is the only living species of this entire phylum Phylum Cycadophyta (cycads, sago palms) Thrived during the “Age of Dinosaurs”; only ~130 species alive today Phylum Gnetophyta 3 genera: Gnetum, Ephedra, Welwitschia Phylum Coniferophyta E.g., longleaf pine, giant sequoia, cypress, and ~600 other cone-bearing species Pine Life Cycle – [See Fig. 30.6] Megasporangia and microsporangia are found in separate cones Meiosis produces spores and begins the haploid generation Megasporocytes (2n) are the cells within megasporangia that undergo meiosis to produce megaspores (n) Microsporocytes (2n) are the cells within microsporangia that undergo meiosis to produce microspores (n) Each megaspore develops into a female gametophyte Each microspore develops into a male gametophyte (a pollen grain) A pollen grain gains access to a female gametophyte through a micropyle The female gametophyte contains 2 or 3 archegonia, each with 1 egg cell Two cells of the male gametophyte are sperm Fertilization (union of 1 egg and 1 sperm) produces an embryo Embryos develop within seeds Seeds germinate and embryos become seedlings ANGIOSPERMS Flowering plants; seeds develop inside sporophyte ovaries ~250,000 extant species 6 main clades [See pg. 602] Anatomy of a Flower – [See Fig. 30.7] Sepals Petals Stamens = {Anthers + Filaments} Carpels = {Stigmas + Styles + Ovaries + Ovules} Receptacle Complete flowers have sepals, petals, stamens & carpels Docsity.com
