1 / 23

Evolution of Seed Plants: Transforming the World

This chapter provides an overview of the evolution of seed plants, focusing on their unique traits such as seeds, reduced gametophytes, heterospory, and pollen. It also explores the advantages of seeds over spores and the characteristics of gymnosperms and angiosperms.

kennethharper
Download Presentation

Evolution of Seed Plants: Transforming the World

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 30 Plant Diversity II: The Evolution of Seed Plants

  2. 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

  3. Fig. 30-UN3 Five Derived Traits of Seed Plants Reducedgametophytes Microscopic male andfemale gametophytes(n) are nourished and protected by thesporophyte (2n) Malegametophyte Femalegametophyte Heterospory Microspore (gives rise toa male gametophyte) Megaspore (gives rise toa female gametophyte) Ovules Integument (2n) Ovule(gymnosperm) Megaspore (2n) Megasporangium (2n) Pollen grains make waterunnecessary for fertilization Pollen Seeds Seeds: survivebetter thanunprotectedspores, can betransportedlong distances Integument Food supply Embryo

  4. Fig. 30-2 PLANT GROUP Mosses and othernonvascular plants Ferns and other seedlessvascular plants Seed plants (gymnosperms and angiosperms) Reduced, independent(photosynthetic andfree-living) Reduced (usually microscopic), dependent on surroundingsporophyte tissue for nutrition Gametophyte Dominant Reduced, dependent ongametophyte for nutrition Sporophyte Dominant Dominant Gymnosperm Angiosperm Sporophyte(2n) Microscopic femalegametophytes (n) insideovulate cone Microscopic femalegametophytes (n) insidethese partsof flowers Sporophyte(2n) Gametophyte(n) Example Microscopic malegametophytes (n) insidethese partsof flowers Microscopic malegametophytes (n) inside pollencone Sporophyte (2n) Sporophyte (2n) Gametophyte(n)

  5. 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

  6. Fig. 30-3-4 From ovule to seed in a gymnosperm Seed coat(derived fromintegument) Integument Femalegametophyte (n) Spore wall Egg nucleus (n) Immaturefemale cone Food supply(femalegametophytetissue) (n) Male gametophyte(within a germinatedpollen grain) (n) Megasporangium(2n) Dischargedsperm nucleus (n) Embryo (2n)(new sporophyte) Micropyle Pollen grain (n) Megaspore (n) (a) Unfertilized ovule (b) Fertilized ovule (c) Gymnosperm seed

  7. 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)

  8. 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

  9. Phylum Gnetophyta (3 genera) • Species vary in appearance, and some are tropical whereas others live in deserts • Largest of the gymnosperm phyla • Most conifers are evergreens and can carry out photosynthesis year round Phylum Coniferophyta

  10. 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

  11. Fig. 30-6-4 Key Haploid (n) Ovule Diploid (2n) Ovulatecone Megasporocyte (2n) Integument Pollencone Microsporocytes(2n) Megasporangium(2n) Maturesporophyte(2n) Pollengrain Pollengrains (n) MEIOSIS MEIOSIS Microsporangia Microsporangium (2n) Survivingmegaspore (n) Seedling Archegonium Femalegametophyte Seeds Foodreserves(n) Spermnucleus (n) Seed coat(2n) Pollentube Embryo(2n) FERTILIZATION Egg nucleus (n)

  12. 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 (ovaryat the base and a styleleading up to a stigma,where pollen is received)

  13. Fig. 30-7 Stigma Carpel Stamen Anther Style Filament Ovary Petal Sepal Ovule

  14. 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)

  15. Tomato Ruby grapefruit Fig. 30-8 Some variations in fruit structure Nectarine Hazelnut Milkweed

  16. Fig. 30- 9 Fruit adaptations that enhance seed dispersal Wings Seeds within berries Barbs

  17. 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 cross-pollinationbtwn flowers from different plants of the same species

  18. 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 food-storing endosperm • Within a seed, the embryo consists of a root and two seed leaves called cotyledons

  19. Fig. 30-10-4 Key Haploid (n) Diploid (2n) Microsporangium Anther Microsporocytes (2n) Mature flower onsporophyte plant(2n) MEIOSIS Generative cell Microspore(n) Ovule (2n) Tube cell Male gametophyte(in pollen grain)(n) Ovary Pollengrains MEIOSIS Germinatingseed Stigma Megasporangium(2n) Pollentube Embryo (2n)Endosperm (3n)Seed coat (2n) Sperm Seed Megaspore(n) Style Antipodal cellsCentral cellSynergidsEgg (n) Female gametophyte(embryo sac) Pollentube Sperm(n) Nucleus ofdevelopingendosperm(3n) FERTILIZATION Zygote (2n) Eggnucleus (n) Discharged sperm nuclei (n)

  20. 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)

  21. Fig. 30-13n Angiosperm diversity MonocotCharacteristics EudicotCharacteristics Embryos Two cotyledons One cotyledon Leafvenation Veins usuallyparallel Veins usuallynetlike Stems Vascular tissueusually arrangedin ring Vascular tissuescattered

  22. Fig. 30-13o Angiosperm diversity MonocotCharacteristics EudicotCharacteristics Roots Taproot (main root)usually present Root systemusually fibrous(no main root) Pollen Pollen grain withone opening Pollen grain withthree openings Flowers Floral organsusually inmultiples of three Floral organs usuallyin multiples of four or five

  23. 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

More Related