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Chapter 12: Diversification of the Eukaryotes: Plants and Fungi Where did all the plants and fungi come from? Lectures by Mark Manteuffel, St. Louis Community College; Clicker Questions by Kristen Curran, University of Wisconsin, Whitewater • Some giant sequoia trees weigh more than a dozen space shuttles. • A mushroom is probably more closely related to animals than it is to any plant. Plant Diversity as a Nonrenewable Resource • Humans depend on plants for thousands of products including food, building materials, and medicines. • The exploding human population is eliminating plant species at an alarming rate. Every 2 seconds humans destroy an area of tropical rain forest equal to the area of 3 football fields Learning Objectives • Know the distinguishing characteristics of the plant kingdom and 4 major plant phyla. • Describe the evolutionary innovations that allowed plants to colonize land. • Understand the alternation of generations in the life cycle of plants. • Describe various relationships between plants and other organisms • Know the distinguishing characteristics of Kingdom Fungi. 12.1 What makes you a plant? Nitrogen, phosphorus, and salts Roots and shoots Dodder: a parasitic plant with “intelligence” 4 Major Plant Phyla Bryophytes 12.2 Colonizing land brings new opportunities and challenges for plants. The First Land Plants Appeared About 475 Million Years Ago Early plants transitioned from algae to moss… The first land plants were small and had no leaves, roots or flowers and could grow only at the water’s edge. Nevertheless, these plants set the stage for the enormous diversity of terrestrial plants and animals on earth today. Living on land poses very different problems from living in water. Cuticle Stomata Vascular tissue (xylem and phloem) Lignin 12.3 Mosses and other non-vascular plants lack vessels for transporting nutrients and water. The Bryophytes include: mosses, liverworts, and hornworts Alternation of Generations • A life cycle of alternating diploid (2n – the sporophyte) and haploid (n gametophyte) generations. • Both generations are multicellular. • Gametophytes produce haploid gametes via mitosis. • Sporophytes produce haploid spores via meiosis. • The Gametophyte generation dominates only in the Bryophyte plant group. A life cycle of alternating haploid and diploid generations in which the diploid embryo is protected by the haploid female Bryophyte Characteristics Non-vascular plants—mosses, liverworts, and hornworts—have scarcely evolved beyond the stage of the earliest land plants. They lack roots and vessels to move water and nutrients from the soil into the plant. They reproduce with spores that form when a sperm from a male reproductive structure “swims” through a drop of rainwater to the egg in a female reproductive structure. Gametophyte generation dominates. 12.4 The evolution of vascular tissue made larger plants possible. Like a circulatory system, vessels are an effective way to carry water and nutrients up from the soil to the leaves. Now the sporophyte generation (diploid adult) dominates: is more conspicuous, is present for a longer period of time in the life cycle, and is responsible for photosynthesis. Seedless Vascular Plant Characteristics • Seedless Vascular plants include ferns and horsetails. • Vascular tissues transport water and nutrients and allow plants to move farther away from water and to grow taller. • Reproduction by haploid spores dispersed by wind or water. • Sprorophyte generation dominates. Seed plants include both Angiosperms and Gymnosperms. Gymnosperms were the first plants to evolve both seeds and pollen. 12.5 What is a seed? Seed = embryo + energy source + protective seed coat Seed Dispersal Only opportunity most plants have to send their offspring away from home Seeds and seed pods have many ways to do this: • forceful send-off of exploding seed pods • seeds that hitch rides on passing animals • seeds that float in water or float through the air Seed dispersal in Angiosperms is aided by delicious fruits. 12.6 With the evolution of the seed, gymnosperms became the dominant plants on Earth. Why would the male cones be on the bottom instead of the top of the pine tree? Now the sporophyte generation is even more dominant. The gametophytes are smaller but are still multicellular. Rigidity, an exterior layer of bark, and the production of sticky sap protects conifers, helping make it possible for conifers to grow taller and reach older ages than any other plants. Gynmosperm Characteristics Gymnosperms include conifers, cycads, gnetophytes, and Ginko. Gymnosperms were the earliest plants to produce seeds and pollen, and this mode of reproduction offers advantages over the spores of earlier plants. The sporophyte generation dominates and in some species can live thousands of years and grow hundreds of feet tall. 95 % of the world’s plants are Angiosperms, which diversified with the mass extinction of the dinosaurs. 12.8 Angiosperms are the dominant plants today. 12.9 A flower is nothing without a pollinator. Most Angiosperms rely in animal pollinators. Why are flowers so flashy? Trickery and Bribery Plant deceit! Recall Orchid species (wasp mimic) • flowers that resemble female wasps • Male wasps are tricked into pollination 2) Bribery Plants offer something of value for pollen transport. Requires: a) b) c) a sticky pollen a flower that catches the attention of the pollinator something of value to the pollinator. Angiosperm reproduction more closely resembles the life cycle of animals: a diploid adult and haploid gametes. Angiosperm characteristics • Angiosperms are the dominant plants today and include all flowering and fruiting plants. • Most angiosperms rely on animals for pollination and seed dispersal. • Reproduction includes double fertilization. • Angiosperm reproduction more closely resembles the life cycle of animals: a diploid sporophyte generation dominates and produces haploid gametes. 12.11 Fleshy fruits are bribes that flowering plants pay animals to disperse seeds. How does this system work? Fruits are colorful Fruits taste good. Fruit is good for animals. Can seeds still sprout after being eaten by an animal? Test it yourself! In fact, dung is a good place for a seed to germinate. 12.12 Unable to escape, plants must resist predation in other ways. Powerful plant alkaloids include caffeine, nicotine, and morphine Some plants enlist the help of friendly insects. Predatory plant: Sundew 12.13 Fungi are closer to animals than they are to plants. Symbionts most often include parasitism or mutualism. 3 Types of Symbioses Symbiosis – an intimate living situation between two or more different species 1. Parasitism – parasite/host relationship where the parasite benefits at the host’s expense 2. Mutualism – both partners benefit 3. Commensalism – one partner benefits, while the other is neither harmed nor benefitted. Examples? A parasite’s commensalistic relationship with the shotgun fungus Some fungi, called yeasts, live as individual cells; most others are multicellular. • 12.14 Fungi have common structures, but exploit an enormous diversity of habitats. Most of the fungal body is underground, secreting enzymes and absorbing food. The mushroom is the aboveground reproductive structure. Fungal Hyphae Mushroom Delicacies Portobello The and shitake mushrooms white button mushroom on pizza Truffles • sell for $1750 to $3500 per pound! How can fungi grow in so many habitats? Advantages of being a decomposer Saprotroph = excretes digestive enzymes outside the body and reabsorbs nutrients. Fungi don’t need light Hyphae have a strong cell wall to penetrate hard substances. Enormously important ecological role! Fungal Parasites • Of the 100,000 known species of fungi, about 30% make their living as parasites • About 50 species of fungi are known to be parasitic in humans and other animals – Yeast infections – Skin disease (Ringworm) – Athlete’s foot • Highly contagious • easily treated • Some fungi produce antibiotics Plants and fungi have a close mutualism. Mycorrhizal fungi grow in intimate association with the roots of most plants, receiving sugar from the plant and transferring nitrogen and phosphorus to the plant. Some plants have turned this relationship into parasitism—these plants lack chlorophyll so they contribute nothing to the fungus, but they receive nutrients from the fungus and sugar from other plants that is delivered via the fungus. Lichens Fungi and chlorophyll-containing bacteria and algae as photosynthetic “partners” Lichens are a pioneer organism. • Through the power of mutualism, the lichen can grow on bare rock, slowly turning that rock into soil. • Soil allows colonization by plants and animals. Characteristics of Fungi • Shared a protist ancestor with animals. • Decomposers/saprotrophs • Composed of hyphae with cell walls of chitin • Are sessile and reproduce by dispersing spores • Some are pathogens of animals and plants. • Some are edible or useful as medicines. • Many have mutualistic partnerships with photosynthetic partners.