ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Thirty-Four Outline INTRODUCTION Dominant Photosynthetic Organisms on Land Predominant Source of Human Food fig 34.1 MONOCOTS AND DICOTS fig 34.4 Two Classes of Anthophyta Monocotyledones: lilies, grasses, cattails, palms Dicotyledones: trees, shrubs, snapdragons, mints Characteristics of monocots Leaves exhibit parallel veins Individual members of whorls in threes Embryos have one cotyledon Single-pored pollen (shared with primitive dicots) Characteristics of dicots Leaves exhibit netlike veins Individual members of whorls in fours or fives Embryos have two cotyledons Three-pored and multipored pollen Additional general differences between monocots and dicots Greater number of dicots than monocots are annuals Monocots more often possess swollen underground storage organs Few monocots are woody Endosperm usually present in mature monocot, not dicot seeds Evolutionary Relationships Dicots are more primitive than monocots Monocots derived from primitive dicots WHY WERE ANGIOSPERMS SUCCESSFUL? Geographical Origins of Angiosperms Originated at time of only two major continental masses Gondwanaland = Africa, South America, Antarctica, India, New Zealand Laurasia = North America, Europe, Asia Evolution occurred within hot, arid interior of Gondwanaland Advantages of Flowering Plants Transport gametes over great distances, promote outcrossing Efficient dispersal via fruit Tough, water resistant leaves for survival in hostile environment Produce natural insecticides The Rise to Dominance Became dominant 80 million years ago in second half of Cretaceous Period Recognize members of present families 65 million years ago Appearance of insects associated with flowers EVOLUTION OF THE FLOWER Structure of Flower Related to Indirect Pollination Life cycle overview Pollen produced in and matures in anthers Pollen tube grows through stigma to ovule Double fertilization of ovule and endosperm nuclei Seed ripens within fruit Specialized pollination Depend on insects and other animals to transport pollen Flowers provide food reward, liquid nectar or pollen Relationships evolved between pollinators and flowering plants Gametes are dispersed as readily as in active animals Characteristics of Floral Evolution Determination of primitive versus specialized flowers Correlate other known primitive features with flower type Compare DNA base pair sequences Analyze fusion or reduction of flower parts Examine features of fossil flowers Characteristics of primitive flowers fig 34.3 Numerous spirally arranged sepals, petals, stamens and carpels Little difference in appearance of sepals and petals Members of whorls are free: not fused with other members of same whorl or members of other whorls Differentiation between floral and vegetative growth Flowers are determinate: apical meristem does not continue to divide after flower is formed Leafy shoots are indeterminate: continue to grow while progressively differentiating new leaves along the shoot Calyx Outer whorl of a complete flower, composed of sepals Similarities in leaves and sepals, share common evolutionary origin Pattern of veins Coloration and form Affected by some of the same genes Corolla Composed of petals Similarities between petals and stamens of most flowering plants Structural similarities Affected by some of the same genes May be homologous, sharing a common origin Exceptions include water lilies fig 34.1a Petals originated as modified sepals Transitional structures between sepals and petals are present Functions to attract pollinators to flower Androecium Composed of stamens: specialized structures that bear microsporangia Probable evolution from small branches containing microsporangia Structure of most stamens includes slender filament and swollen anther Primitive stamens are flattened and leaf-like Gynoecium Composed of carpels, traditionally called pistil Primitive plants have leaflike carpels Highly specialized organs unique to flowering plants Ovules occur within lower portion, called ovary Slender style between ovary and receptive stigma TRENDS OF FLORAL SPECIALIZATION Involve Aggregation of and/or Reduction in Flower Parts fig 34.4 Reduction in number of parts in each whorl Spiral pattern evolves into single whorl at each level Central axis shortens, whorls close together Fusion of members of whorls, frequently joined into a tube Fusion among whorls or loss of whole whorls Factors Promoting Outcrossing Flower structure Most flowers possess both stamens and carpels Pistillate flowers possess carpels (pistils), lack stamens Staminate flowers possess stamens, lack carpels Presence of flowers on whole plants Dioecious: staminate and pistillate flowers on separate individuals Example: willow Outcrossing is complete Monoecious: staminate and pistillate flowers on the same individual Example: oaks and birches, corn, ragweed fig 34.5 Outcrossing enhanced by differential maturation of flowers Dichogamous: flowers possess both pistils and stamens, but they mature at different times Either may mature first, flower may be staminate then pistillate fig 34.6 Significantly increases outcrossing rate Physical separation of pistils and stamens Genetic self-incompatibility Pollen from an individual will not function on its own stigma Embryos from self-fertilization abort soon after fertilization Trends in Floral Symmetry Primitive flowers are radially symmetrical Advanced flowers are generally bilaterally symmetrical Example: orchids fig 34.1d;4b Tubular flowers having advanced pollination systems are common POLLINATION IN FLOWERING PLANTS Pollination in Early Seed Plants Passive pollination by the wind Requires production of great quantities of pollen Individuals must grow relatively close together A few gymnosperms are insect pollinated Pollination by Animals Important role in evolutionary success of angiosperms Earliest angiosperms and perhaps ancestors were insect pollinated Coevolution between plants and animals affects floral specialization Bees and Flowers Bees are most common insect pollinators fig 20.5;34.7 Ability to locate flowers Initially by odor Secondarily orient by shape, color, texture Bee pollinated flowers are generally blue or yellow Nectaries identified by lines of dots or stripes Food produced for bees by flowers Few obtain nectar, primarily food source for adult forms Generally obtain pollen, food source for larvae Social structure of bee populations Few are social or semisocial Produce several generations during one year Visit different kinds of flowers throughout a season Utilize many different flowers at one time due to colony size Most bees are solitary Visit only a small group of generally related plants Result in frequent evolutionary modifications Insects Other Than Bees Specialized mouthparts of butterflies and moths Characteristics of flowers visited by butterflies Flat landing platforms Long, tubular floral tubes filled with nectar Characteristics of flowers visited by moths Pale coloration, yellow or white Heavily scented for locating at night Long floral tubes Pollination by Birds Hummingbirds are most common pollinators fig 34.8 Floral characteristics Production of large quantities of nectar Red coloration that is not conspicuous to insects Contrary to carotenoid pigments in yellow flowers Reflect in ultraviolet range, called "bee`s purple" fig 34.9 Odorless because birds do not have well-developed olfactory senses Floral tubes strong to withstand beak of birds Wind-Pollinated Angiosperms Examples: oaks, birches, cottonwoods, grasses, sedges and nettles Characteristics of flowers Small, greenish, odorless fig 34.5;10 Corollas reduced or absent Occur in large, close groupings May hang down in tassels May be monoecious or dioecious Self-Pollination Occurs relatively frequently Flowers small and inconspicuous Pollen shed directly onto stigma, often before flower opens Rationale supporting self-pollination Ecologically advantageous where animal pollinators are scarce Advantageous to maintain genetic similarity in uniform habitats Many weeds self-pollinate THE EVOLUTION OF FRUITS Fruit Dispersed When Used as Food Fleshy coverings Shiny black, blue or bright red coloration fig 34.3c;11b Parallel Evolution of Generalized Adaptations Hooks and spines attach seeds to passing animals fig 34.11a Seeds buried for food, but never reclaimed Many seeds are dispersed by the wind Winged seeds of pines and maples Fuzzy seeds of dandelion, milkweed, willow and cottonwood fig 34.12 Dustlike seeds of orchids Dispersal by water Example: coconut Important to island colonization fig 20.4