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Adaptations Enabling the Move to Land • The movement onto land by ancestors provided unfiltered sun, more plentiful CO2, nutrient-rich soil, and few herbivores or pathogens • Land presented challenges: a scarcity of water and lack of structural support Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Terrestrial plants are characterized by • Chlorophylls a and b and carotenoids in their chloroplast • Food stored as starch • Cell walls of cellulose • Sporic sexual reproduction involving an alternation of sporophyte and gametophyte generations Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings SPORIC SEXUAL REPRODUCTION Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Origin and Diversification of Plants • Fossil evidence indicates that plants were on land at least 475 million years ago • Fossilized spores and tissues have been extracted from 475-million-year-old rocks • First land animal=428 million years ago Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Those ancestral species gave rise to a vast diversity of modern plants • Land plants can be informally grouped based on the presence or absence of vascular tissue • Most plants have vascular tissue; these constitute the vascular plants • Nonvascular plants are commonly called bryophytes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Seedless vascular plants Pterophytes (ferns and their relatives) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • A seed is an embryo and nutrients surrounded by a protective coat • Seed plants form a clade and can be divided into further clades: – Gymnosperms, the “naked seed” plants, including the conifers – Angiosperms, the flowering plants Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 29.2: Mosses and other nonvascular plants have life cycles dominated by gametophytes • Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants: – Liverworts, phylum Hepatophyta – Mosses, phylum Bryophyta • Mosses are most closely related to vascular plants Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Key Bryophyte traits • Lack vascular tissue • Lack true leaves, roots, and leaves • Gametophyte dominant life cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyte Gametophytes • In all bryophyte phyla, gametophytes are larger and longer-living than sporophytes • Sporophytes are typically present only part of the time Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Multicellular Gametangia • Gametes are produced within organs called gametangia • Female gametangia, called archegonia, produce eggs and are the site of fertilization • Male gametangia, called antheridia, are the site of sperm production and release Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyta Life Cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • A spore germinates into a gametophyte composed of a protonema and gameteproducing gametophore • Rhizoids anchor gametophytes to substrate • The height of gametophytes is constrained by lack of vascular tissues • Mature gametophytes produce flagellated sperm in antheridia and an egg in each archegonium • Sperm swim through a film of water to reach and fertilize the egg Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyte Sporophytes • Bryophyte sporophytes grow out of archegonia, and are the smallest and simplest sporophytes of all extant plant groups • A sporophyte consists of a foot, a seta (stalk), and a sporangium, also called a capsule, which discharges spores through a peristome • Hornwort and moss sporophytes have stomata for gas exchange Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-9d Polytrichum commune, hairy-cap moss Capsule Seta Sporophyte (a sturdy plant that takes months to grow) Gametophyte Traits of Vascular Plants • Living vascular plants are characterized by: • Life cycles with dominant sporophytes • Vascular tissues called xylem and phloem • Well-developed roots and leaves Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall • Vascular tissue allowed these plants to grow tall WHAT IS AN ADVANTAGE OF HEIGHT? • Seedless vascular plants have flagellated sperm and are usually restricted to moist environments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Pterophyta (Seedless Vascular plant) Key Traits • Vascular tissue • Sporophyte dominant • Surface water required for sperm mobility Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Pterophyta Life Cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Life Cycles with Dominant Sporophytes • In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern • The gametophytes are tiny plants that grow on or below the soil surface Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Transport in Xylem and Phloem • Vascular plants have two types of vascular tissue: xylem and phloem • Xylem conducts most of the water and minerals and includes dead cells called tracheids • Phloem consists of living cells and distributes sugars, amino acids, and other organic products • Water-conducting cells are strengthened by lignin and provide structural support • Increased height was an evolutionary advantage Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution of Roots • Roots are organs that anchor vascular plants • They enable vascular plants to absorb water and nutrients from the soil • Roots may have evolved from subterranean stems • What would water transport allow? Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Plant can now get water easier and have support but how do they get away from needing a moist env.? Seeds • Gymnosperm-exposed seeds – Phylum Coniferophyta • Angiosperms-enclosed seeds – Phylum Anthophyta Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Transforming the World • Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems • A seed consists of an embryo and nutrients surrounded by a protective coat Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Evolutionary Advantage of Seeds • A seed develops from the whole ovule • A seed 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 Concept 30.1: Seeds and pollen grains are key adaptations for life on land • In addition to seeds, the following are common to all seed plants – Reduced gametophytes – Ovules – Pollen Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ovules and Production of Eggs • An ovule consists of a megasporangium, megaspore, and one or more protective integuments • Gymnosperm megaspores have one integument • Angiosperm megaspores usually have two integuments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Pollen and Production of Sperm • Microspores develop into pollen grains, which contain the male gametophytes • Pollination is the transfer of pollen to the part of a seed plant containing the ovules • Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals • If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 30.2: Gymnosperms bear “naked” seeds, typically on cones • The gymnosperms have “naked” seeds not enclosed by ovaries and consist of four phyla: – Coniferophyta (conifers, such as pine, fir, and redwood) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phylum Coniferophyta • This phylum is by far the 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 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 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Coniferophyta Life Cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Characteristics of Angiosperms • All angiosperms are classified in a single phylum, Anthophyta • The name comes from the Greek anthos, flower • Angiosperms are seed plants with reproductive structures called flowers and fruits • They are the most widespread and diverse of all plants Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Flowers • The flower is an angiosperm structure specialized for sexual reproduction • Many species are pollinated by insects or animals, while some species are windpollinated Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-7 Stigma Stamen Anther Pistil Style Filament Ovary Petal Sepal Ovule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • A pistil consists of an 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 Fruits • A fruit typically consists of a mature ovary but can also include other flower parts • Fruits protect seeds and aid in their dispersal • Mature fruits can be either fleshy or dry Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-8 Tomato Ruby grapefruit Nectarine Hazelnut Milkweed Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Various fruit adaptations help disperse seeds • Seeds can be carried by wind, water, or animals to new locations 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 • The ovule is entered by a pore called the micropyle • Double fertilization occurs when the pollen tube discharges two sperm into the female gametophyte within an ovule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • One sperm fertilizes the egg, while the other combines with two nuclei in the central cell of the female gametophyte and initiates development of food-storing endosperm • The endosperm nourishes the developing embryo • 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 Anthophyta Life Cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Assignments 1. All-Only Draw Antheridium and Archegonium 2. All-Antheridium and Archegonium can be drawn as on Prothallium for g 3. All-Only draw Mature pollen grains, Ovulate cone, Staminate cone 4. Only a,c,d,e,f 5. Omit Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings