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BIOLOGY A GUIDE TO THE NATURAL WORLD FOURTH EDITION DAVID KROGH The Angiosperms: Form and Function in Flowering Plants Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. 25.1 Two Ways of Categorizing Flowering Plants Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Categorizing Flowering Plants • Plants can be categorized by how long it takes them to go through a cycle that runs from germination to death. • Those that go through this cycle in a year or less are annuals; those that go through it in about 2 years are biennials; those that live for many years are perennials. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Categorizing Flowering Plants Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.4 Categorizing Flowering Plants • A cotyledon is an embryonic leaf, present in the seed. • Angiosperms are classified according to how many cotyledons they have: – one in the case of the narrow-leafed monocotyledons – two in the case of the broad-leafed dicotyledons Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Categorizing Flowering Plants Monocots Dicots one cotyledon two cotyledons embryonic leaves mature leaves narrow leaves parallel veins broad leaves branching veins roots fibrous root system taproot system vascular bundles scattered throughout stem arranged in ring in stem type of growth only primary growth may have secondary woody growth flower parts multiples of three multiples of four or five examples orchids, wheat, rice, bananas oak and maple trees, cacti, sunflowers Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.5 Categorizing Flowering Plants • Monocots and dicots differ in structure in many ways. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Categorizing Flowering Plants Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.6 25.2 There Are Three Fundamental Types of Plant Cells Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Types of Plant Cells • There are three fundamental types of cells in plants that, alone or in combination, make up most of the plant’s tissues, meaning groups of cells that carry out a common function. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Types of Plant Cells • These three cell types are: – parenchyma – sclerenchyma – collenchyma Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 25.3 The Plant Body and Its Tissue Types Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Plant Body and Its Tissue Types • Some plants are capable only of primary growth, meaning growth at the tips of their roots and shoots that primarily increases their length. • Plants that exhibit only primary growth are herbaceous plants, composed solely of primary tissue. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Plant Body and Its Tissue Types • Other plants exhibit both vertical growth and lateral, or secondary, growth. • These are the woody plants, composed of primary and secondary tissue. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Plant Body and Its Tissue Types • There are four tissue types in the primary plant body: – – – – dermal vascular meristematic ground Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Four Types of Tissue dermal tissue vascular tissue ground tissue meristematic tissue Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.8 Four Types of Tissue • • • • Dermal tissue is the plant’s outer covering. Vascular tissue is its “plumbing.” Meristematic tissue is its growth tissue. Ground tissue is almost everything else in the plant. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Dermal Tissue Dermal Tissue invaders out sunlight gases in exchanged cuticle epidermis guard cells of stomata trichome guard cells: epidermal cells trichomes: hairlike outgrowths modified for regulation of gas exchange of epidermal cells Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.9 Ground Tissue Ground Tissue parenchyma • thin-walled • alive at maturity • many functions collenchyma • wall irregularly thick • structural support (plastic) sclerenchyma • very thick-walled • dead at maturity • structural support (stiff) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.10 Vascular Tissue Vascular Tissue vascular bundle phloem xylem vessel element tracheid sieve element Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. companion cell Figure 25.11 Plant Tissue and Growth PLAY Animation 25.1: Plant Tissue and Growth Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 25.4 How a Plant Grows: Apical Meristems Give Rise to the Entire Plant Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. How a Plant Grows • The entire plant develops from meristematic cells in regions called apical meristems. • Meristematic cells remain perpetually embryonic, able to continually give rise to cells that differentiate into all the plant’s tissue types. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. How a Plant Grows • Shoot apical meristems give rise to the entire shoot of the plant. • In addition to providing for vertical growth, shoot apical meristems produce meristematic tissue called lateral buds at the base of leaves. • Lateral buds can give rise to a branch or flower. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. How a Plant Grows Meristematic Tissue immature leaf shoot apical meristem (terminal bud) meristematic tissue (lateral bud) root apical meristem root cap Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.13 How a Plant Grows • Root apical meristems are located just behind a collection of cells at the very tip of the root, called the root cap. • The plant’s tissue types develop in stages from meristematic cells. • This development takes place in a series of regions adjacent to the apical meristem. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. How a Plant Grows • In a gradual transition, the apical meristem gives way to a zone of cell division. • This is followed by a zone of elongation (in which developing cells lengthen). • This is followed by a zone of differentiation (in which cells fully differentiate into different tissue types). Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Tissue Development from Apical Meristems dermal tissue zone of differentiation ground vascular tissue tissue root hairs zone of elongation zone of cell division meristem root cap Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.15 25.5 Secondary Growth Comes from a Thickening of Two Types of Tissue Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Secondary Growth Tissues • Secondary growth in plants takes place through the division of cells in two varieties of meristematic tissue that develop only in woody plants: – Vascular cambium, which continually produces secondary phloem and secondary xylem tissue layers to either side of itself. – Cork cambium, which gives rise to the outer tissues of woody plants. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. primary growth Secondary Growth Tissues secondary growth Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.18 Secondary Growth Tissues primary xylem primary phloem vascular cambium first-year growth secondary xylem secondary phloem second-year growth third-year growth lateral growth vascular secondary secondary cambium xylem phloem Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.19 Secondary Growth Tissues • Secondary xylem, also known as wood, is responsible for most of a tree’s widening. • Looking at a tree from the secondary phloem outward to the tree’s periphery, four tissues constitute the tree’s bark: – – – – secondary phloem phelloderm cork cambium cork Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Secondary Growth Tissues cork cork cambium bark phelloderm secondary phloem vascular cambium secondary xylem (wood) xylem ray Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.22 Secondary Growth Tissues • The cork cells are dead in their mature state and provide layers of protection for the tree. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 25.6 How the Plant’s Vascular System Functions Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Xylem • Two types of cells make up the waterconducting portions of xylem tissue: tracheids and vessel elements, both of which are dead in their mature, working state. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Xylem • Vessel elements, which exist almost solely in angiosperms, conduct more water than tracheids. • Their existence in angiosperms is one of the reasons for the angiosperms’ dominance in the plant world. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Xylem xylem tracheid vessel element Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.25 Xylem • Water movement through xylem is driven by transpiration, meaning the loss of water from a plant, mostly through the leaves. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Xylem Water Transport by Transpiration H2O H2O Water evaporates from stomata on underside of leaves. plant’s energy not required Water from stem is pulled up through xylem to replace water lost from leaves. Water is pulled out of soil into roots to replace water lost from stem. H2O Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.26 Xylem • As water evaporates into the air, it pulls a continuous column of water upward through the plant. • The energy for this process comes from the sun, whose rays power the evaporation of water at the leaf surface. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Phloem • The sugar sucrose is the main product that flows through phloem. • The fluid-conducting cells in phloem, sieve elements, lack cell nuclei in maturity. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Phloem • Each sieve element has associated with it one or more companion cells, which retain their nuclei and seem to take care of the housekeeping needs of their related sieve elements. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Phloem phloem sieve element companion cell Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.27 Water Transport in Plants Suggested Media Enhancement: Water Transport in Plants To access this animation go to folder C_Animations_and_Video_Files and open the BioFlix folder. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Phloem • Plants expend their own energy to load the sucrose they produce into the phloem’s sieve element cells. • Once this takes place, there is a greater concentration of solutes inside the cells than outside them—a condition that brings about a flow of water into the cells through osmosis. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sugar Transport by Pressure Flow Sugar Transport by Pressure Flow source Photosynthesis in leaves produces sugar, which is loaded into the phloem. plant’s energy required Sugars are transported through phloem to fruits, stems, and roots. Sugars are stored in parenchyma. sink Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.28 Sugar Transport by Pressure Flow • The pressure that results from the increased water inside the cells is sufficient to move the solution of water and dissolved sucrose through the sieve element cells. • They move from “source” (the cells into which the sugar was loaded) to “sink” (the cells in which the sugar is stored or used). Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Phloem Sap Transport and Phloem-Xylem Linkage xylem source sugar phloem Sugar is actively transported into phloem (requires plant’s own energy). water leaf cell Water follows by osmosis. Pressure gradient moves fluid down phloem. sink sugar Sugar moves by active or passive transport into root cell. water root cell Water follows by osmosis. vessel sieve element element Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.30 Vascular System PLAY Animation 25.2: The Vascular System for Plants Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 25.7 Sexual Reproduction in Flowering Plants Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sexual Reproduction in Flowering Plants • All plants, including angiosperms, reproduce through an alternation of generations. • A sporophyte generation (the familiar tree or flower) produces haploid spores that develop into their own generation of plant, the gametophyte generation. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sexual Reproduction • In angiosperms, the male gametophyte is the pollen grain, consisting in maturity of an outer coat, two sperm cells, and one tube cell. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sexual Reproduction • The female angiosperm gametophyte consists at maturity of an embryo sac composed of seven cells, one of which is the egg. • The female gametophyte is housed inside a structure of the parent sporophyte plant called an ovule. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sexual Reproduction anther ovary pollen sac ovule microspore mother cell (2n) meiosis megaspore mother cell (2n) 4 microspores (n) integument micropyle stalk 4 megaspores (n) mitosis 3 megaspores degenerate mitosis mitosis tube cell generative cell mitosis pollen grain tube cell outer coat sperm cells pollen (male gametophyte) is released from sporophyte plant it’s housed in mitosis embryo sac 8 haploid nuclei cytokinesis egg central cell mature female gametophyte within sporophyte The male gametophyte generation takes shape inside the chambers of the pollen sacs, where the diploid microspore mother cells will undergo meiosis, each one of them thereby giving rise to four haploid microspores. These microspores represent the new, haploid generation of the plant on the male side. For the female gametophyte generation, development begins in a structure inside the parent ovary called an ovule. A single diploid megaspore mother cell in the ovule undergoes meiosis, producing four haploid megaspores. This marks the beginning of the female gametophyte generation. The single cell in each microspore goes through cell division, thereby producing two cells, a tube cell and a generative cell. Before or during this time, a protective coat develops around the microspore. The combination of the cells and protective coat is the pollen grain. At some point, the generative cell in the grain divides into two sperm cells. With this cell division, a mature male gametophyte has developed. The pollen grain is then released from the anthers to make its way to a stigma. Three of the megaspores then die. The remaining megaspore undergoes mitosis, eventually producing six cells with a single nucleus each and one central cell with two nuclei. These seven cells form the embryo sac, which is the mature female gametophyte. One of the seven cells in the embryo sac is the egg that will undergo fertilization by one of the sperm in the pollen grain. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.34 Sexual Reproduction • Fertilization of the egg by sperm requires that a pollen grain land on the stigma of a plant. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sexual Reproduction • The tube cell of the pollen grain then germinates, sprouting a pollen tube that grows down through the sporophyte plant’s stigma and style, eventually reaching the female reproductive cells inside the ovule. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sexual Reproduction • The sperm cells inside the pollen grain travel down through the pollen tube, and one of the sperm cells fertilizes the egg in the ovule, producing a zygote. • With this, the new sporophyte generation of plant has come into being. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sexual Reproduction anther mature sporophyte pollen microspores carpel ovary gametophyte generation (n) tube cell sperm cells pollen germination stigma pollen tube seed germination and growth megaspore sporophyte generation (2n) egg fertilization seed zygote embryo Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.33 Sexual Reproduction • The second sperm cell in the pollen grain enters the central cell in the embryo sac, setting in motion the development of food for the embryo, endosperm tissue. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sexual Reproduction • This second fertilization completes the process of double fertilization—a fusion of gametes on the one hand and of cells producing nutritive tissue on the other. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sexual Reproduction tube cell sperm cells pollen grain stigma pollen tube sperm cells style fusion of one sperm cell with nuclei of central cell to form endosperm (3n) micropyle ovary ovule with female gametophyte egg (n) pollination pollen tube growth double fertilization Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. fusion of one sperm cell with egg to form zygote (2n) Figure 25.35 25.8 Embryo, Seed, and Fruit: The Developing Plant Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Developing Plant • With fertilization, the ovule integuments that surrounded the embryo sac begin to develop into the seed coat that will surround the growing sporophyte embryo. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Developing Plant • The ovary that surrounded the ovule then starts to develop into a layer of tissue that will surround the seed: fruit, which is defined as the mature ovary of a flowering plant. • Under this definition the pod of a pea plant is fruit, as is the flesh of an apricot. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Developing Plant Apricot Pea Strawberry carpels one carpel, one seed one carpel, many seeds many carpels, many seeds, one receptacle receptacle Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 25.38 The Developing Plant • The seed with its fruit covering eventually separates from the sporophyte parent plant and then germinates in the Earth. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Plant Reproduction PLAY Animation 25.3: Plant Reproduction Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.