Chapter 30: Plant Diversity II By Dan Xiang, Sam Taylor, and Graham Opie Important Terms • • • • • Bryophyte - Non vascular terrestrial plants Gametophyte - Haploid generation of plants Sporophyte - Diploid generation of plants Integument - Layers of sporophyte tissue Heterospory - Production of two spores male and female by the sporophyte of land plants • Double fertilization - One sperm fertilizes egg, another fuses with the two nuclei found in the large central cell of the female gametophyte Overview • Seed developed around 360 million years ago. • The harvesting of gymnosperms and angiosperms (mainly angiosperms) allowed humans to have permanent settlement. • Most plants today are classified as either a gymnosperm or an angiosperm 30.1 The reduced gametophytes of seed plants are protected in ovules and pollen grains • The first known seeded plants cames into existence more than 360 million years ago • The evolution of seeds allowed plants to become the dominant producers in most of the terrestrial ecosystems. • Seeded plants began to make up the vast majority of plant biodiversity. • During permian period arid climates let gymnosperms thrive. (think moss preproduction) Adaptations of seed plants • • • • • Reduced gametophytes Heterospory Ovules Pollen Cotyledons and endosperms Reduced gametophytes • Seedless plants have lifecycles that are dominated by gametophytes • Seeded plants lifecycles are dominated by sporophyte stage. • Miniaturization of the gametophyte stage lets the gametophyte develop from a spore inside of the sporangia. Heterosporous vs Homosporous • Seedless plants are almost all homosporous and thus have bisexual gametophytes • Seed plants are heterosporous • Some seedless plants are heterosporous • Female gametophyte in a heterosporous plant is called the megaspore • Male gametophyte in a heterosporous plant is called the microspore Diagram of ovule (and pollen) Heterospore difference continued/ ovule section • Though some seedless plants can be heterosporous, seed plants are unique in that they keep the megaspore within the parent sporophyte • While inside the sporophyte the megasporangia is enveloped by an integument(s) in order to protect the megaspore Heterospory/pollen • Microspores develop into pollen grains, they carry the male gametophyte • The pollen has a hard coat of the polymer sporopollenin (not a hard term to remember for once) • Pollen can travel very long distances especially compared to the sperm of seedless plants. Advantages of seeds • The seed allows for a greater chance that the ovule will be pollinated safely and that the zygote (embyro) will remain safe until it matures. • Helps the plant thrive or reproduce easier in harsh climates. • Being able to travel farther enables the new plant that is born from the seed to not have to share its resources with its parent as often. • Cotyledons and endosperms 30.2 Gymnosperms bear “naked” seeds, typically on cones • Their seeds are considered “naked” • They are the first form of seed plants • Some of the most common gymnosperms are conifers, or cone-bearing plants • The transitional plants between seedless plants and gymnosperms are called progymnosperms… • The four phyla of gymnosperms are cycads, ginkgo, gnetophytes, and conifers. Naked seeds • In naked seeds the endosperm is haploid • Conifers have male and female cones, the pollen from male cone fertilizes the haploid ovules of the female cone then a diploid cell is produced (embryo) • Other gymnosperms have similar setups but with seeds on their leaves instead of protective cone seed. http://www.youtube.com/watch?v=D9byVQxv MXs Life Cycle of a Pine 30.3 The reproductive adaptations of angiosperms include flowers and fruits • • • • 90% of Plantae Kingdom 250,000 known species Phylum Anthophyta Flower Structure unique to Angiosperm sexual reproduction • Pollen transportation Flower Structure Angiosperm Reproduction Function of Fruits • Mechanism to disperse seeds • Consists of a mature ovary • Pollination occurs->ovary wall becomes a pericarp->the rest of the flower withers away • Pollination does not occur->flower just withers away • Fruits are either fleshy or dry Fruit Adaptations • • • • • • Fruits adapt to disperse seeds Winged seeds Water dispersal (i.e. Coconut) Fruit with burrs can cling Edible, nutritious, sweet, colorful Purpose of double fertilization is preventing flower from wasting resources http://www.youtube.com/watch?v=Gq8NWh9 8wQs Angiosperm Origins and Evolution • First Angiosperms developed 140 mya • Archaefructus liaoningensis & Archaefructus sinensis- 125 million years old • Comparison of A. sinensis with 173 species of modern angiosperms • Michael Frohlich- “evo-devo” approach. • Ancestor had separate ovule and pollen producing structures Cont. • Mutations occurred and ovule developed on some microsporophyll • “Mostly male” hypothesis • Gene comparison between gymnosperm pollen producing genes and flower development genes Angiosperm Diversity • Monocots- “One” “Cotyledon” i.e. orchids, palms, corn, wheat, rice- ¼ angiosperms • Dicots- “Two” Cotyledon” i.e. roses, peas, sunflowers • Dicots->Eudicots • Basal angiosperms Evolutionary Links between Angiosperms and Animals • Animals create a selective pressure for plants and vice versa • Mutual evolutionary relationship benefits both partners • Bees/hummingbird and angiosperm relationship increases diversity in both 30.4 Human welfare depends greatly on seed plants • 80% of all the food we eat comes from angiosperms • Modern crops come from recent changes to plant diversity, humans selected for more fitting traits in plants • About 25% of medicine contains ingredients from angiosperms, wood is very important to human development. Cont. • Deforestation is causing the most drastic rate of decrease in plant diversity since Permian and Cretaceous extinctions. • The loss of plant diversity equates to the loss in diversity of many other species because seed plants are often the building blocks of ecosystems. Works Cited • • • • • "1-introduction of lima bean - Classification explinations: comparing angiosperms and gymnosperms." 1-introduction of lima bean - Just another Edublogs.org weblog. N.p., n.d. Web. 13 Nov. 2011. <http://brubini4662.edublogs.org/2010/05/27/classification-explinationscomparing-angiosperms-and-gymnosperms/>. "Biology 2108." College of Science and Mathematics. N.p., n.d. Web. 13 Nov. 2011. <http://science.kennesaw.edu/~jdirnber/Bio2108/Lecture/LecBiodiversity/Bio DivPlants.html>. "[ Plant Life Cycle Phases - Phase One ( Planting Seeds ) ]." Welcome to Penn State York. N.p., n.d. Web. 13 Nov. 2011. <http://www2.yk.psu.edu/~sg3/ist311/games/team3/>. kelikelvin19. " Seed Production in Gymnosperm - YouTube ." YouTube - Broadcast Yourself. . N.p., n.d. Web. 13 Nov. 2011. <http://www.youtube.com/watch?v=D9byVQxvMXs>. leoquartz06. " Seed Production in Gymnosperm - YouTube ." YouTube - Broadcast Yourself. . N.p., n.d. Web. 13 Nov. 2011. <http://www.youtube.com/watch?v=D9byVQxvMXs>.