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    Plant diversity.ppt Plant diversity.ppt Document Transcript

    • Plant Diversity PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings charophyceans as the closest relatives of land plants –  Rose-shaped complexes for cellulose synthesis Coleochaete Nitella •  There are four key traits that land plants share only with charophyceans Chara 30 nm Figure 29.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Genetic Evidence –  Peroxisome enzymes –  Structure of flagellated sperm –  Formation of a phragmoplast •  Comparisons of both nuclear and chloroplast genes –  Point to charophyceans as the closest living relatives of land plants (a) Chara, a pond organism 10 mm 40 µm Figure 29.3a, b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Coleochaete orbicularis, a diskshaped charophycean (LM) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1
    • Adaptations Enabling the Move to Land •  In charophyceans –  A layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  Land plants possess a set of derived terrestrial adaptations •  Many adaptations –  Emerged after land plants diverged from their charophycean relatives Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Defining the Plant Kingdom •  Systematists –  Are currently debating the boundaries of the plant kingdom Viridiplantae Streptophyta Plantae Red algae Figure 29.4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chlorophytes Charophyceans Embryophytes Ancestral alga Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Derived Traits of Plants •  Five key traits appear in nearly all land plants but are absent in the charophyceans •  Apical meristems and alternation of generations APICAL MERISTEMS Apical meristem of shoot Developing leaves Apical meristems of plant shoots and roots. The light micrographs are longitudinal sections at the tips of a shoot and root. –  Apical meristems –  Alternation of generations Apical meristem of root –  Walled spores produced in sporangia –  Multicellular gametangia Shoot 100 µm Haploid multicellular organism (gametophyte) Mitosis ALTERNATION OF GENERATIONS –  Multicellular dependent embryos Root 100 µm Mitosis n n Spores n n n Gametes MEIOSIS FERTILIZATION 2n Diploid multicellular organism (sporophyte) Figure 29.5 2n Zygote Mitosis Alternation of generations: a generalized scheme Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 29.5 2
    • •  Walled spores; multicellular gametangia; and multicellular, dependent embryos GAMETOPHYTE (n) mitosis Spores (n) Archegonium Antheridium (n) (n) produce meiosis Sporocyte (2n) HAPLODIPLONTIC ("Alternation of Gen erations") Egg (n) Sporangium (2n) Sperm (n) } lost by reduction and modification in the Angiosperms WALLED SPORES PRODUCED IN SPORANGIA and some Gnetales Sporophyte and sporangium of Sphagnum (a moss) Sporophyte Gametophyte MULTICELLULAR GAMETANGIA Female gametophyte Archegonium with egg Embryo (2n) mitosis Antheridium with sperm Archegonia and antheridia of Marchantia (a liverwort) Male gametophyte Zygote mitosis Longitudinal section of Sphagnum sporangium (LM) (Sperm non-flagellate in Conifers, Gnetales, and Angiosperms) fertilization SPOROPHYTE (2n ) Spores Sporangium MULTICELLULAR, DEPENDENT EMBRYOS (2n) Embryo and placental transfer cell of Marchantia Figure 29.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Embryo Maternal tissue 2 µm 10 µm Wall ingrowths Placental transfer cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Origin and Diversification of Plants •  Additional derived units •  Fossil evidence –  Such as a cuticle and secondary compounds, evolved in many plant species Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings –  Indicates that plants were on land at least 475 million years ago Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  Fossilized spores and tissues –  Have been extracted from 475-million-year-old rocks (a) Fossilized spores. Unlike the spores of most living plants, which are single grains, these spores found in Oman are in groups of four (left; one hidden) and two (right). •  Whatever the age of the first land plants –  Those ancestral species gave rise to a vast diversity of modern plants (b) Fossilized Figure 29.6 a, b sporophyte tissue. The spores were embedded in tissue that appears to be from plants. Table 29.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3
    • •  An overview of land plant evolution Land plants Vascular plants Gymnosperms Angiosperms Seed plants Pterophyte (ferns, horsetails, whisk fern) Lycophytes (club mosses, spike mosses, quillworts) Seedless vascular plants Mosses Hornworts Charophyceans Liverworts Bryophytes (nonvascular plants) Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) The life cycles of mosses and other bryophytes are dominated by the gametophyte stage Origin of land plants (about 475 mya) Ancestral green alga Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bryophyte Gametophytes •  Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants –  Liverworts, phylum Hepatophyta •  In all three bryophyte phyla –  Gametophytes are larger and longer-living than sporophytes –  Hornworts, phylum Anthocerophyta –  Mosses, phylum Bryophyta Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  The life cycle of a moss Raindrop Key Male gametophyte 1 Spores develop into threadlike protonemata. •  Bryophyte diversity Haploid (n) Diploid (2n) Sperm Gametophore of female gametophyte “Bud” 2 The haploid protonemata produce “buds” that grow into gametophytes. Protonemata 4 A sperm swims through a film of moisture to an archegonium and fertilizes the egg. Antheridia 3 Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively. LIVERWORTS (PHYLUM HEPATOPHYTA) Plagiochila deltoidea, a “leafy” liverwort Foot “Bud” Seta Egg Spores Marchantia polymorpha, a “thalloid” liverwort Sporangium MEIOSIS Mature Mature sporophytes sporophytes Capsule (sporangium) Calyptra Zygote Marchantia sporophyte (LM) FERTILIZATION (within archegonium) HORNWORTS (PHYLUM ANTHOCEROPHYTA) An Anthoceros hornwort species Embryo Sporophyte Foot Sporangium 500 µm Gametophore Female Archegonia Meiosis occurs and haploid gametophyte spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the Rhizoid peristome “teeth” regulate 6 The sporophyte grows a gradual release of the spores. long stalk, or seta, that emerges Seta from the archegonium. 8 Peristome MOSSES (PHYLUM BRYOPHYTA) Polytrichum commune, hairy-cap moss Sporophyte Archegonium Capsule with peristome (LM) Figure 29.8 Female gametophytes Young 5 The diploid zygote sporophyte develops into a sporophyte embryo within Attached by its foot, the the archegonium. sporophyte remains nutritionally dependent on the gametophyte. Gametophyte 7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gametophyte Figure 29.9 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4
    • Ecological and Economic Importance of Mosses •  Sphagnum, or “peat moss” •  Ferns and other seedless vascular plants –  Forms extensive deposits of partially decayed organic material known as peat –  Plays an important role in the Earth’s carbon cycle (a) Peat being harvested from a peat bog (b) Closeup of Sphagnum. Note the “leafy” gametophytes and their offspring, the sporophytes. Gametophyte Sporangium at tip of sporophyte Living photo- Dead watersynthetic storing cells cells 100 µm (c) Sphagnum “leaf” (LM). The combination of living photosynthetic cells and dead water-storing cells gives the moss its spongy quality. Figure 29.10 a–d (d) “Tolland Man,” a bog mummy dating from 405–100 B.C. The acidic, oxygen-poor conditions produced by Sphagnum canpreserve human or other animal bodies for thousands of years. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  Ferns and other seedless vascular plants formed the first forests •  Bryophytes and bryophyte-like plants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  These early tiny plants –  Had independent, branching sporophytes –  Lacked other derived traits of vascular plants –  Were the prevalent vegetation during the first 100 million years of plant evolution •  Vascular plants –  Began to evolve during the Carboniferous period Figure 29.11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life Cycles with Dominant Sporophytes •  In contrast with bryophytes •  The life cycle of a fern –  Sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern 1 Sporangia release spores. Most fern species produce a single type of spore that gives rise to a bisexual gametophyte. Key 2 The fern spore develops into a small, photosynthetic gametophyte. 3 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanisms promote cross-fertilization between gametophytes. Haploid (n) Diploid (2n) Antheridium Spore MEIOSIS –  The gametophytes are tiny plants that grow on or below the soil surface Young gametophyte Sporangium Archegonium Mature sporophyte New sporophyte Sperm Egg Zygote Sporangium FERTILIZATION Sorus 6 On the underside of the sporophyte‘s reproductive leaves are spots called sori. Each sorus is a cluster of sporangia. Gametophyte Fiddlehead Figure 29.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4 Fern sperm use flagella to swim from the antheridia to eggs in the archegonia. 5 A zygote develops into a new sporophyte, and the young plant grows out from an archegonium of its parent, the gametophyte. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5
    • Transport in Xylem and Phloem •  Vascular plants have two types of vascular tissue –  Xylem and phloem •  Xylem –  Conducts most of the water and minerals –  Includes dead cells called tracheids •  Phloem –  Distributes sugars, amino acids, and other organic products –  Consists of living cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of Roots Evolution of Leaves •  Roots •  Leaves –  Are organs that anchor vascular plants –  Enable vascular plants to absorb water and nutrients from the soil –  Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis –  May have evolved from subterranean stems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  Leaves are categorized by two types –  Microphylls, leaves with a single vein –  Megaphylls, leaves with a highly branched vascular system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  According to one model of evolution –  Microphylls evolved first, as outgrowths of stems Vascular tissue Figure 29.13a, b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (a) Microphylls, such as those of lycophytes, may have originated as small stem outgrowths supported by single, unbranched strands of vascular tissue. (b) Megaphylls, which have branched vascular systems, may have evolved by the fusion of branched stems. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 6
    • Sporophylls and Spore Variations Classification of Seedless Vascular Plants •  Sporophylls •  Seedless vascular plants form two phyla –  Are modified leaves with sporangia •  Most seedless vascular plants –  Are homosporous, producing one type of spore that develops into a bisexual gametophyte Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings –  Lycophyta, including club mosses, spike mosses, and quillworts –  Pterophyta, including ferns, horsetails, and whisk ferns and their relatives Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  The general groups of seedless vascular plants LYCOPHYTES (PHYLUM LYCOPHYTA) Strobili (clusters of sporophylls) Isoetes gunnii, a quillwort Selaginella apoda, a spike moss Diphasiastrum tristachyum, a club moss PTEROPHYTES (PHYLUM PTEROPHYTA) Psilotum nudum, a whisk fern Equisetum arvense, field horsetail Athyrium filix-femina, lady fern Vegetative stem Strobilus on fertile stem Figure 29.14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings WHISK FERNS AND RELATIVES HORSETAILS FERNS Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives •  Modern species of lycophytes •  Ferns –  Are relics from a far more eminent past –  Are the most diverse seedless vascular plants –  Are small herbaceous plants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 7
    • The Significance of Seedless Vascular Plants •  The ancestors of modern lycophytes, horsetails, and ferns –  Grew to great heights during the Carboniferous, forming the first forests •  The growth of these early forests –  May have helped produce the major global cooling that characterized the end of the Carboniferous period –  Decayed and eventually became coal Figure 29.15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  Seeds changed the course of plant evolution The Evolution of Seed Plants –  Enabling their bearers to become the dominant producers in most terrestrial ecosystems PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Figure 30.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Advantages of Reduced Gametophytes •  The reduced gametophytes of seed plants are protected in ovules and pollen grains •  In addition to seeds, the following are common to all seed plants •  The gametophytes of seed plants –  Develop within the walls of spores retained within tissues of the parent sporophyte –  Reduced gametophytes –  Heterospory –  Ovules –  Pollen Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8
    • Heterospory: The Rule Among Seed Plants •  Gametophyte/sporophyte relationships Sporophyte (2n) Sporophyte (2n) Gametophyte (n) (a) Sporophyte dependent on gametophyte (mosses and other bryophytes). Gametophyte (n) –  Which produce megaspores that give rise to female gametophytes (b) Large sporophyte and small, independent gametophyte (ferns and other seedless vascular plants). Microscopic female gametophytes (n) in ovulate cones (dependent) Microscopic female gametophytes (n) inside these parts of flowers (dependent) Microscopic male gametophytes (n) inside these parts of flowers (dependent) Microscopic male gametophytes (n) in pollen cones (dependent) •  Seed plants evolved from plants that had megasporangia •  Seed plants evolved from plants that had microsporangia –  Which produce microspores that give rise to male gametophytes Sporophyte (2n), the flowering plant (independent) Sporophyte (2n) (independent) (c) Reduced gametophyte dependent on sporophyte (seed plants: gymnosperms and angiosperms). Figure 30.2a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ovules and Production of Eggs Pollen and Production of Sperm •  An ovule consists of •  Microspores develop into pollen grains –  A megasporangium, megaspore, and protective integuments Integument Spore wall Megasporangium (2n) –  Which contain the male gametophytes of plants •  Pollination –  Is the transfer of pollen to the part of a seed plant containing the ovules Megaspore (n) (a) Unfertilized ovule. In this sectional view through the ovule of a pine (a gymnosperm), a fleshy megasporangium is surrounded by a protective layer of tissue called an integument. (Angiosperms have two integuments.) Figure 30.3a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  If a pollen grain germinates –  It gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule Female gametophyte (n) –  Eliminated the water requirement for fertilization Egg nucleus (n) Spore wall Male gametophyte (within germinating pollen grain) (n) Discharged sperm nucleus (n) Micropyle Figure 30.3b •  Pollen, which can be dispersed by air or animals Pollen grain (n) (b) Fertilized ovule. A megaspore develops into a multicellular female gametophyte. The micropyle, the only opening through the integument, allows entry of a pollen grain. The pollen grain contains a male gametophyte, which develops a pollen tube that discharges sperm. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9
    • The Evolutionary Advantage of Seeds •  A seed –  Develops from the whole ovule –  Is a sporophyte embryo, along with its food supply, packaged in a protective coat Seed coat (derived from Integument) •  Gymnosperms bear “naked” seeds, typically on cones •  Among the gymnosperms are many wellknown conifers –  Or cone-bearing trees, including pine, fir, and redwood Food supply (female gametophyte tissue) (n) Embryo (2n) (new sporophyte) (c) Figure 30.3c 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 integument. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  The gymnosperms include four plant phyla –  Cycadophyta –  Gingkophyta –  Gnetophyta –  Coniferophyta Cycas Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cycas revoluta Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 10
    • Ginkgo biloba Ginkgo biloba Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Conifer Diversity Female cone Ginkgo biloba Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Araucariaceae Cupressaceae Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11
    • Pinaceae: Pinus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gymnosperm Evolution •  Fossil evidence reveals that by the late Devonian –  Some plants, called progymnosperms, had begun to acquire some adaptations that characterize seed plants Figure 30.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 12
    • A Closer Look at the Life Cycle of a Pine •  Gymnosperms appear early in the fossil record –  And dominated the Mesozoic terrestrial ecosystems •  Key features of the gymnosperm life cycle include –  Dominance of the sporophyte generation, the pine tree •  Living seed plants –  Can be divided into two groups: gymnosperms and angiosperms –  The development of seeds from fertilized ovules –  The role of pollen in transferring sperm to ovules Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  The life cycle of a pine 2 An ovulate cone scale has two ovules, each containing a megasporangium. Only one ovule is shown. Key 1 In most conifer species, each tree has both ovulate and pollen cones. Haploid (n) Diploid (2n) Ovule Pollen cone Integument Longitudinal section of ovulate cone Microsporocytes (2n) Mature sporophyte (2n) MEIOSIS Seedling 3 Micropyle Megasporangium Longitudinal section of Sporophyll pollen cone Microsporangium Germinating pollen Pollen grain grains (n) MEIOSIS (containing male gametophytes) Surviving megaspore (n) A pollen cone contains many microsporangia held in sporophylls. Each microsporangium Germinating contains microsporocytes (microspore mother pollen grain cells). These undergo meiosis, giving rise to Archegonium haploid microspores that develop into Egg (n) Integument pollen grains. Female Seeds on surface gametophyte A pollen grain enters through the micropyle and germinates, forming a pollen tube that slowly digests through the megasporangium. 4 Megasporocyte (2n) Ovulate cone 5 While the pollen tube develops, the megasporocyte (megaspore mother cell) undergoes meiosis, producing four haploid cells. One survives as a megaspore. of ovulate scale Germinating pollen grain (n) 8 Fertilization usually occurs more than a year after pollination. All eggs may be fertilized, but usually only one zygote develops into an embryo. The ovule becomes a seed, consisting of an embryo, food supply, and seed coat. Figure 30.6 Embryo (new sporophyte) (2n) Food reserves (gametophyte tissue) (n) Seed coat (derived from parent sporophyte) (2n) Discharged sperm nucleus (n) Pollen tube FERTILIZATION Egg nucleus (n) The female gametophyte 6 develops within the megaspore and contains two or three archegonia, each with an egg. •  The reproductive adaptations of angiosperms include flowers and fruits •  Angiosperms –  Are commonly known as flowering plants –  Are seed plants that produce the reproductive structures called flowers and fruits –  Are the most widespread and diverse of all plants 7 By the time the eggs are mature, two sperm cells have developed in the pollen tube, which extends to the female gametophyte. Fertilization occurs when sperm and egg nuclei unite. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Characteristics of Angiosperms Flowers •  The key adaptations in the evolution of angiosperms •  The flower –  Are flowers and fruits Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings –  Is an angiosperm structure specialized for sexual reproduction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 13
    • Fruits •  A flower is a specialized shoot with modified leaves –  Sepals, which enclose the flower •  Fruits –  Typically consist of a mature ovary (a) Tomato, a fleshy fruit with soft outer and inner layers of pericarp –  Petals, which are brightly colored and attract pollinators (b) Ruby grapefruit, a fleshy fruit with a hard outer layer and soft inner layer of pericarp –  Stamens, which produce pollen –  Carpels, which produce ovules (c) Nectarine, a fleshy fruit with a soft outer layer and hard inner layer (pit) of pericarp Carpel Stigma Anther Stamen Style Ovary Filament Petal Sepal Receptacle Figure 30.7 Ovule Figure 30.8a–e Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (d) Milkweed, a dry fruit that splits open at maturity (e) Walnut, a dry fruit that remains closed at maturity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Angiosperm Life Cycle •  Can be carried by wind, water, or animals to new locations, enhancing seed dispersal (a) Wings enable maple fruits to be easily carried by the wind. •  In the angiosperm life cycle –  Double fertilization –  One sperm fertilizes the egg, while the other combines with two nuclei in the center cell of the female gametophyte and initiates development of food-storing endosperm (b) Seeds within berries and other edible fruits are often dispersed in animal feces. •  The endosperm –  Nourishes the developing embryo (c) Figure 30.9a–c The barbs of cockleburs facilitate seed dispersal by allowing the fruits to “hitchhike” on animals. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fossil Angiosperms •  The life cycle of an angiosperm Key Haploid (n) Diploid (2n) Microsporangium Anther Microsporocytes (2n) Mature flower on sporophyte plant (2n) 2 Microspores form pollen grains (containing male gametophytes). The generative cell will divide to form two sperm. The tube cell will produce the pollen tube. –  Display both derived and primitive traits Carpel MEIOSIS Microspore (n) Ovule with megasporangium (2n) 7 When a seed germinates, the embryo develops into a mature sporophyte. Generative cell Embryo (2n) Endosperm (food Supply) (3n) Seed Pollen grains MEIOSIS 3 In the megasporangium of each ovule, the megasporocyte divides by meiosis and produces four megaspores. The surviving megaspore in each ovule forms a female gametophyte (embryo sac). Stamen Tube cell Male gametophyte (in pollen grain) Ovary Germinating Seed 6 The zygote develops into an embryo that is packaged along with food into a seed. (The fruit tissues surrounding the seed are not shown). •  Primitive fossils of 125-million-year-old angiosperms 1 Anthers contain microsporangia. Each microsporangium contains microsporocytes (microspore mother cells) that divide by meiosis, producing microspores. Stigma Megasporangium (n) Surviving megaspore (n) Seed coat (2n) Pollen tube Sperm Pollen tube 5 cm Style Female gametophyte (embryo sac) Antipodal cells Polar nuclei Synergids Egg (n) Pollen tube (a) Archaefructus sinensis, a 125-million-yearold fossil. Zygote (2n) Nucleus of developing endosperm (3n) Egg Nucleus (n) Sperm (n) 5 Figure 30.10 Double fertilization occurs. One sperm fertilizes the egg, forming a zygote. The other sperm combines with the two polar nuclei to form the nucleus of the endosperm, which is triploid in this example. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Artist’s reconstruction of Archaefructus sinensis 4 After pollination, eventually two sperm nuclei are discharged in each ovule. FERTILIZATION Discharged sperm nuclei (n) Figure 30.11a, b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 14
    • Angiosperm Diversity •  The two main groups of angiosperms –  Are monocots and eudicots •  Basal angiosperms –  Are less derived and include the flowering plants belonging to the oldest lineages •  Magnoliids –  Share some traits with basal angiosperms but are more closely related to monocots and eudicots Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings •  Exploring Angiosperm Diversity •  Exploring Angiosperm Diversity BASAL ANGIOSPERMS EUDICOTS MONOCOTS Monocot Characteristics Orchid (Lemboglossum fossii) Eudicot Characteristics California poppy (Eschscholzia californica) Embryos One cotyledon Two cotyledons Leaf venation Amborella trichopoda Eudicots Monocots Magnoliids Star anise and relatives Amborella Water lilies HYPOTHETICAL TREE OF FLOWERING PLANTS Pygmy date palm (Phoenix roebelenii) Pyrenean oak (Quercus pyrenaica) Veins usually netlike Veins usually parallel Star anise (Illicium floridanum) Water lily (Nymphaea “Rene Gerard”) Stems Lily (Lilium “Enchantment”) Vascular tissue usually arranged in ring Vascular tissue scattered Roots Root system Usually fibrous (no main root) Barley (Hordeum vulgare), a grass Taproot (main root) usually present Dog rose (Rosa canina), a wild rose Pea (Lathyrus nervosus, Lord Anson’s blue pea), a legume Pollen MAGNOLIIDS Pollen grain with one opening Pollen grain with three openings Flowers Anther Southern magnolia (Magnolia grandiflora) Stigma Figure 30.12 Figure 30.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Filament Ovary Floral organs usually in multiples of three Floral organs usually in multiples of four or five Zucchini (Cucurbita Pepo), female (left) and male flowers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolutionary Links Between Angiosperms and Animals Products from Seed Plants •  Pollination of flowers by animals and transport of seeds by animals •  Humans depend on seed plants for –  Are two important relationships in terrestrial ecosystems (a) A flower pollinated by honeybees. This honeybee is harvesting pollen and nectar (a sugary solution secreted by flower glands) from a Scottish broom flower. The flower has a tripping mechanism that arches the stamens over the bee and dusts it with pollen, some of which will rub off onto the stigma of the next flower the bee visits. (b) A flower pollinated by hummingbirds. The long, thin beak and tongue of this rufous hummingbird enable the animal to probe flowers that secrete nectar deep within floral tubes. Before the hummer leaves, anthers will dust its beak and head feathers with pollen. Many flowers that are pollinated by birds are red or pink, colors to which bird eyes are especially sensitive. Figure 30.13a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings –  Food –  Wood –  Many medicines (c) A flower pollinated by nocturnal animals. Some angiosperms, such as this cactus, depend mainly on nocturnal pollinators, including bats. Common adaptations of such plants include large, light-colored, highly fragrant flowers that nighttime pollinators can locate. Table 30.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 15