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Transcript
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: Evolutionary advances over lower vascular plants • Fully adapted to life on land, even dry places • Posses woody tissue made of xylem which transports water, minerals and supports the plant • Grows in diameter and height • Reproduction involved wind borne pollen and seeds and does not require water 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 What human reproductive organ is analogous to this seed? 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 which are retained within the sporophyte, and are dependent on the sporophyte – Heterospory – two types of spores produced – megasporangia produce megaspores that give rise to female gametophytes, and microsporangia produce microspores that give rise to male gametophytes – Ovules – a structure made up of megasporangium, megaspore, and their integument(s) (a protective layer of tissue ) – Pollen – consists of a male gametophyte enclosed within the pollen wall Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings This is a great review of plant life cycles 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) Fig. 30-3-1 Integument Spore wall Immature female cone Megasporangium (2n) Megaspore (n) (a) Unfertilized ovule 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 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 Fig. 30-3-4 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: (Do not memorize!) – Cycadophyta (cycads) – Gingkophyta (one living species: Ginkgo biloba) – Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) – Coniferophyta (conifers, such as pine, fir, and redwood) Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-5k Sequoia Fig. 30-5l Wollemi pine Fig. 30-5m Common juniper 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 life cycle of a pine provides an example • 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) The Life Cycle of a Pine - Animation • http://bcs.whfreeman.com/thelifewire/content/chp30/30020.html (Pine tree life cycle) • http://www.youtube.com/watch?v=D9byVQxvMXs Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 30.3: The reproductive adaptations of angiosperms include flowers and fruits • Angiosperms are seed plants with reproductive structures called flowers and fruits • They are the most widespread and diverse of all plants Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Characteristics of Angiosperms • • Reasons for evolutionary success – Superior competitors – Coevolution with animals that acted as pollinators – The flower The flower – Flower parts are modified leaves of the sporophyte generation – Pollen grains are immature male gametophytes – Female gametophytes are enclosed inside female flower parts – Seeds develop inside fruits (the fruit is the mature ovary) – Double fertilization is a reproductive feature of flowering plants – The endosperm (the seed food supply) results from double fertilization 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 wind-pollinated • A flower is a specialized shoot with up to four types of modified leaves: – Sepals, which enclose the flower – Petals, which are brightly colored and attract pollinators – Stamens, which produce pollen on their terminal anthers – Carpels, which produce ovules Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-7 Stigma Stamen Anther Carpel Style Filament Ovary Petal Sepal Ovule 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 • Various fruit adaptations help disperse seeds • Seeds can be carried by wind, water, or animals to new locations Animation: Fruit Development • http://www.youtube.com/watch?v=bwCpQflmQG4&feature=related Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 30-8 Tomato Ruby grapefruit Nectarine Hazelnut Milkweed Fig. 30-9 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 cross-pollination between flowers from different plants of the same species • 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 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 Life Cycle • http://www.youtube.com/watch?v=htMZYR1nCOQ&feature=related Double fertilization in an angiosperm • http://www.youtube.com/watch?v=H_UyDtaa8Ow&feature=related Life Cycle of a Flowing Plant Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolutionary Links Between Angiosperms and Animals • Pollination of flowers and transport of seeds by animals are two important relationships in terrestrial ecosystems • Co-evolution – reciprocal adaptations • http://www.youtube.com/watch?v=0mchJw5Dz7g pollination Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Hummingbird Concept 30.4: Human welfare depends greatly on seed plants • No group of plants is more important to human survival than seed plants • Plants are key sources of food, fuel, wood products, and medicine • Our reliance on seed plants makes preservation of plant diversity critical • Most of our food comes from angiosperms • Six crops (wheat, rice, maize, potatoes, cassava, and sweet potatoes) yield 80% of the calories consumed by humans • Modern crops are products of relatively recent genetic change resulting from artificial selection • Many seed plants provide wood • Secondary compounds of seed plants are used in medicines Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 30-1a Threats to Plant Diversity • Destruction of habitat is causing extinction of many plant species • Loss of plant habitat is often accompanied by loss of the animal species that plants support • At the current rate of habitat loss, 50% of Earth’s species will become extinct within the next 100–200 years Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings You should now be able to: 1. Explain why pollen grains were an important adaptation for successful reproduction on land 2. Explain how fruits may be adapted to disperse seeds 3. Describe the current threat to plant diversity caused by human population growth Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings