BIOL 102 Ch. 30 (Plant Diversity II: The Evolution of Seed Plants)
BIOL 102 Ch. 30 (Plant Diversity II: The Evolution of Seed Plants) BIO 102
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This 6 page Class Notes was uploaded by Zach Notetaker on Tuesday October 4, 2016. The Class Notes belongs to BIO 102 at University of South Carolina taught by Mihaly Czako in Fall 2016. Since its upload, it has received 8 views.
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Date Created: 10/04/16
BIOL 102 Ch.30 Lecture Notes (Plant Diversity II: The Evolution of See Plants) 5 Derived Traits of Seed Plants Reduced gametophytes Microscopic male and female gametophytes (n) nourished and protected by sporophyte (2n) Heterospory Microspore (gives rise to male gametophyte) Megaspore (gives rise to female gametophyte) Ovules Ovule (gymnosperm) • Integument (2n) • Megaspore (n) • Megasporangium (2n) Pollen Pollen grains make water unnecessary for fertilization Seeds Seeds: survive better than unprotected spores, can be transported long distances • Seed coat • Food supply • Embryo • Transforming the World: o Seeds changed course of plant evolution enabling bearers to become dominant producers in terrestrial ecosystems o Seed = embryo and nutrients surrounded by protective coat § Can disperse over long distances by wind or other means • Common traits to seed plants (derived traits) o Reduced gametophytes § Advantages: • Develop w/in walls of spores that are retained w/in tissues of parent sporophyte (dependent gametophyte) o Heterospory § Megasporangia produce megaspores that give rise to female gametophyte § Microsporangia produce microspores that give rise to male gametophytes o Ovules § Ovule: consists of megasporangium, megaspore, + 1 or more protective integuments § Gymnosperm megasporangia have 1 integument § Angiosperm megasporangia usually have 2 integuments o Pollen § Microspores develop into pollen grains (contain male gametophytes) § Pollination: transfer of pollen to part of a seed plant containing ovules § Eliminates need for film of water and can be dispersed great distances by air or animals § Pollen grain germinates à gives rise to pollen tube that discharges sperm into female gametophyte with ovule § Sporopollenin of pollen grain has function like seed coat (most durable organic polymer) • Evolutionary Advantage of Seeds: o Seeds develop from whole ovule o Seed is sporophyte embryo, along w/ food supply, packed in protective coat! o Some evolutionary advantages over spores: § May remain dormant for days to years, until conditions favorable for germination § Seeds have supply of stores food § May be transplanted long distances by wind or animals • Gymnosperms have “naked” seeds, typically on cones o Seeds are exposed on sporophylls that form cones o Angiosperms found in fruits, which are mature ovaries o Cone-bearing plants à conifers o Diversity: § Angiosperms dominate more terrestrial ecosystems, though conifers still dominate ecosystem in regions including northern latitudes § Four phyla: • Cycadophyta (cycads) o Flagellated sperm • Gingkophyta (one living species: Ginkgo biloba) o Flagellated sperm o High tolerance to air pollution and popular ornamental tree • Gentophyta (three genera: Gnetum, Ephedra, Welwitschia) • Coniferophyta (conifers, such as pine, fir, and redwood) o Largest gymnosperm phyla o Most are evergreens and carry out photosynthesis year round 2 o Needlelike leaves, w/ adaptive advantage of decreased surface area, reducing water loss • Angiosperms are seed plants w/ reproductive structures called flowers and fruits o Most widespread and diverse of all plants • Characteristics of Angiosperms: o SINGLE PHYLUM, Anthophyta o 2 Key adaptations: § Flowers • Specialized for sexual reproduction • Many are pollinated by insects or animals while some species are wind-pollinated • Flowers that have all 4 organs called complete flowers • Those lacking one or more organs called incomplete flowers • Specialized shoot w/ up to 4 types of modified leaves called floral organs: o Sepals: enclose the flower o Petals: brightly colored and attract pollinators o Stamens: produce pollen § Consists of stalk called filament, sac called anther where pollen is produced o Carpels: produce ovules § Consists of an ovary @ base and style leading up to a stigma, where pollen is received • Symmetry: o Radial symmetry: § For flowers w/ this any imaginary line thru central axis divides the flower into 2 equal parts 3 o Bilateral symmetry: § Flower can only be divided into 2 equal parts by a single imaginary line • Perfect flowers: flowers w/ both functional stamens and carpals • Imperfect flowers: flowers w/ stamens and carpals that occur on separate flowers § Fruits • Formed when ovary wall thickens and matures • Fruits protect seeds and aid in their dispersal • Mature fruits can be either fleshy or dry • Various adaptations help disperse seeds • Angiosperm Life Cycle o Flower of sporophyte composed of BOT male and female structures o Male gametophytes contained w/in pollen grains produced by microsporangia of anthers o Female gametophyte or embryo sac: develops w/in ovule contained w/in ovary @ base of stigma o Most flowers have mechanisms to ensure cross-pollination b/w flowers from different paths of same species o Pollen grain lands on stigma, germinates and pollen tube of male gametophytes grows down to ovary o Ovule entered by pore called micropyle o Double fertilization occurs when pollen tube discharges 2 sperm into female gametophyte w/in ovule and 2 things form: zygote and endosperm o 1 sperm fertilizes egg, other combines w/ 2 nuclei in central cell of female gametophyte and initiates development of food-storing endosperm o The triploid endosperm nourishes developing embryo § w/in a seed, embryo consists of root and 2 seed leaves called cotyledons 4 • Angiosperm Phylogeny: o Ancestors of angiosperms and gymnosperms diverges 305 million yrs ago o May be closely related to Bennettitales, extinct seed plants w/ flowerlike structures o Amborella & water lilies likely descended from 2 of most ancient angiosperm lineages • Evolutionary Links w/ Animals: o Animals influence evolution of plants and vice versa § Ex) herbivory selects for plant defenses § Ex) interactions b/w pollinators and flowering plants select for mutually beneficial adaptations o Bilateral symmetry affects movement of pollinators & reduces diverging populations § Plants w/ this may have increased rates of speciation • Angiosperm Diversity: o Comprise 250,000+ living species o Previously 2 main groups § Monocots (one cotyledon) • More than ¼ of angiosperms species are these • Largest groups à orchids, grasses, & palms § Dicots (two cotyledons) • More than 2/3 angiosperm species are these • Include large legume family and rose family § DNA studies suggest dicots are PARAPHYLETIC • Human Welfare & Seed Plants: o Key sources of food, fuel, wood products, medicine 5 o Reliance on seed plants makes preservation of plant diversity critical o Products from seed plants: § Most food from angiosperms § 6 crops yield 80% of calories consumed by humans § Modern crops = products of relatively recent genetic change resulting from artificial selection § Many seed plants provide wood § Secondary compounds of seed plants used in medicines • Threats to Plant Diversity o Destruction of habitat § Reduces absorption of atmospheric CO2 that occurs during photosynthesis o Loss of accompanied animal species o Tropical rain forests = medical compounds? 6
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