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Chapter 30 Plant Diversity II: The Evolution of Seed Plants PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Transforming the World (Common to all seed plants) • Seed - embryo and nutrients surrounded by a protective coat • Reduced gametophytes - develop within the walls of spores & retained within tissues of the parent sporophyte • Heterospory (male and female parts) • Ovules - consists of a megasporangium, megaspore, and one or more protective integuments (Gymnosperm have 1; Angiosperm have 2) • Pollen - Pollen grains contain the male gametophytes. If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule • Pollination - transfer of pollen to the part of a seed plant containing the ovules Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-UN3 Five Derived Traits of Seed Plants Reduced gametophytes Heterospory Microscopic male and female gametophytes (n) are nourished and protected by the sporophyte (2n) Male gametophyte Female gametophyte Microspore (gives rise to a male gametophyte) Megaspore (gives rise to a female gametophyte) Ovules Integument (2n) Ovule (gymnosperm) Megaspore (2n) Megasporangium (2n) Pollen Pollen grains make water unnecessary for fertilization Seeds Seeds: survive better than unprotected spores, can be transported long distances Integument Food supply Embryo Fig. 30-2 PLANT GROUP Mosses and other nonvascular plants Gametophyte Dominant Sporophyte Ferns and other seedless vascular plants Seed plants (gymnosperms and angiosperms) Reduced, independent (photosynthetic and free-living) Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Reduced, dependent on Dominant gametophyte for nutrition Dominant Gymnosperm Sporophyte (2n) Microscopic female gametophytes (n) inside ovulate cone Sporophyte (2n) Gametophyte (n) Angiosperm Microscopic female gametophytes (n) inside these parts of flowers Example Microscopic male gametophytes (n) inside pollen cone Sporophyte (2n) Gametophyte (n) Microscopic male gametophytes (n) inside these parts of flowers Sporophyte (2n) The Evolutionary Advantage of Seeds • develops from the whole ovule • is a sporophyte embryo, along with its food supply, packaged in a protective coat • Seeds provide some evolutionary advantages over spores: – They may remain dormant for days to years, until conditions are favorable for germination – They may be transported long distances by wind or animals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-3-4 From ovule to seed in a gymnosperm Integument Female gametophyte (n) Seed coat (derived from integument) Spore wall Egg nucleus (n) Immature female cone Megasporangium (2n) Megaspore (n) (a) Unfertilized ovule Male gametophyte (within a germinated pollen grain) (n) Micropyle (b) Fertilized ovule Food supply (female gametophyte tissue) (n) Discharged sperm nucleus (n) Pollen grain (n) Embryo (2n) (new sporophyte) (c) Gymnosperm seed Concept 30.2: Gymnosperms bear “naked” seeds, typically on cones • The gymnosperms have “naked” seeds not enclosed by ovaries and consist of four phyla: – Cycadophyta (cycads) – Gingkophyta (one living species: Ginkgo biloba) – Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) – Coniferophyta (conifers, such as pine, fir, and redwood) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phylum Cycadophyta • Large cones and palmlike leaves. These thrived during the Mesozoic, but relatively few species exist today. Phylum Ginkgophyta •This phylum consists of a single living species, Ginkgo biloba •It has a high tolerance to air pollution and is a popular ornamental tree Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phylum Gnetophyta (3 genera) • Species vary in appearance, and some are tropical whereas others live in deserts Phylum Coniferophyta • Largest of the gymnosperm phyla • Most conifers are evergreens and can carry out photosynthesis year round Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Life Cycle of a Pine: A Closer Look • Three key features of the gymnosperm life cycle are: – Dominance of the sporophyte generation – Development of seeds from fertilized ovules – The transfer of sperm to ovules by pollen • The pine tree is the sporophyte and produces sporangia in male and female cones • Small cones produce microspores called pollen grains, each of which contains a male gametophyte • The familiar larger cones contain ovules, which produce megaspores that develop into female gametophytes • It takes nearly three years from cone production to mature seed Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-6-4 Key Haploid (n) Diploid (2n) Ovule Ovulate cone Pollen cone Megasporocyte (2n) Integument Microsporocytes (2n) Megasporangium Pollen (2n) Pollen grain grains (n) MEIOSIS MEIOSIS Mature sporophyte (2n) Microsporangia Microsporangium (2n) Seedling Archegonium Female gametophyte Seeds Food reserves (n) Seed coat (2n) Embryo (2n) Sperm nucleus (n) Pollen tube FERTILIZATION Egg nucleus (n) Surviving megaspore (n) Characteristics of Angiosperms • All angiosperms are classified in a single phylum, Anthophyta (Greek anthos, flower) • Flower - angiosperm structure specialized for sexual reproduction • A flower is a specialized shoot with up to four types of modified leaves: – Sepals - enclose the flower – Petals - brightly colored & attract pollinators – Stamens - produce pollen on terminal anthers – Carpels - produce ovules (ovary at the base and a style leading up to a stigma, where pollen is received) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-7 Stigma Stamen Anther Carpel Style Filament Ovary Petal Sepal Ovule Fruits • Fruit - typically consists of a mature ovary but can also include other flower parts – protect seeds & aid in dispersal – can be either fleshy or dry – adaptations help disperse seeds(wind, water, or animals) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Tomato Ruby grapefruit Fig. 30-8 Some variations in fruit structure Nectarine Hazelnut Milkweed Fig. 30- 9 Fruit adaptations that enhance seed dispersal Wings Seeds within berries Barbs The Angiosperm Life Cycle • The flower of the sporophyte is composed of both male and female structures • Male gametophytes are contained within pollen grains produced by the microsporangia of anthers • The female gametophyte, or embryo sac, develops within an ovule contained within an ovary at the base of a stigma • Most flowers have mechanisms to ensure crosspollination btwn flowers from different plants of the same species Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • A pollen grain that has landed on a stigma germinates and the pollen tube of the male gametophyte grows down to the ovary • Micropyle – pore in the ovule • Double fertilization - pollen tube discharges two sperm into the female gametophyte within an ovule • One sperm fertilizes the egg • the other combines with two nuclei in the central cell of the female gametophyte and initiates development of foodstoring endosperm • Within a seed, the embryo consists of a root and two seed leaves called cotyledons Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-10-4 Key Haploid (n) Diploid (2n) Mature flower on sporophyte plant (2n) Microsporangium Microsporocytes (2n) Anther MEIOSIS Ovule (2n) Microspore (n) Ovary Germinating seed MEIOSIS Megasporangium (2n) Embryo (2n) Endosperm (3n) Seed Seed coat (2n) Nucleus of developing endosperm (3n) Male gametophyte (in pollen grain) Pollen (n) grains Stigma Pollen tube Megaspore (n) Antipodal cells Female gametophyte Central cell (embryo sac) Synergids Egg (n) Generative cell Tube cell Sperm Style Pollen tube Sperm (n) FERTILIZATION Zygote (2n) Egg nucleus (n) Discharged sperm nuclei (n) Angiosperm Diversity • The two main groups of angiosperms are monocots (one cotyledon) and eudicots (“true” dicots) • Basal angiosperms - less derived and include the flowering plants belonging to the oldest lineages (Eg. Amborella trichopoda, water lilies, and star anise) • Magnoliids - share some traits with basal angiosperms but are more closely related to monocots and eudicots (Eg. magnolias, laurels, and black pepper plants) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-13n Angiosperm diversity Monocot Characteristics Eudicot Characteristics Embryos Two cotyledons One cotyledon Leaf venation Veins usually parallel Veins usually netlike Stems Vascular tissue scattered Vascular tissue usually arranged in ring Fig. 30-13o Angiosperm diversity Monocot Characteristics Eudicot Characteristics Roots Taproot (main root) usually present Root system usually fibrous (no main root) Pollen Pollen grain with one opening Pollen grain with three openings Flowers Floral organs usually in multiples of three Floral organs usually in multiples of four or five Evolutionary Links Between Angiosperms and Animals • Pollination of flowers and transport of seeds by animals are two important relationships in terrestrial ecosystems • Clades with bilaterally symmetrical flowers have more species than those with radially symmetrical flowers • This is likely because bilateral symmetry affects the movement of pollinators and reduces gene flow in diverging populations Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings