Chapter 28 Lecture Presentation - Green Algae and Land Plants PDF

Introduction to Biology II Chapter 28 Green Algae and Land Plants Chapter 28 Opening Roadmap Chapter 28 Learning Objectives At the completion of this section, you should be able to ….. Des...

Introduction to Biology II Chapter 28 Green Algae and Land Plants Chapter 28 Opening Roadmap Chapter 28 Learning Objectives At the completion of this section, you should be able to ….. Describe plant ecosystem services and foods, medicines, and materials plants provide humans. Interpret a basic phylogenetic tree that shows the relationships among all major plants groups (green algae, nonvascular plants, vascular seedless plants, gymnosperms, and angiosperms) with the main synapomorphies defined (e.g. vascular tissue, flowers, stomata, cuticle, seeds etc.) Contrast the life cycles of the major terrestrial plant groups with regard to alternation of generations: nonvascular plants, vascular seedless plants, gymnosperms, and angiosperms. Explain how a given adaptation reduces the challenges of terrestrial life for plants in terms of acquiring carbon and nutrients, reproduction, capturing light, or keeping cells moist. Introduction Viridiplantae: Eukaryotic clade with 500,000 species, playing vital roles in terrestrial and aquatic ecosystems. Green Plants: 1. Green algae: important photosynthetic organisms in freshwater habitats 2. Land plants: key photosynthesizers in terrestrial environments Introduction Green Algae: Traditionally protists studied for being closest to land plants. Land Plants: First organisms thriving with tissues exposed to air, transforming Earth's nature. Paved the way for terrestrial life. Before land plants, limited to bacteria, archaea, and single-celled protists. 28.1 Why Do Biologists Study Green Algae and Land Plants? Why do biologists study green algae and land plants? Essential organisms: Provide food, fuel, fibers, and pharmaceuticals. Crucial industries: Agriculture, forestry, and horticulture. Issues: Weeds and invasive species. Plants Provide Ecosystem Services Ecosystem: all organisms and nonliving components in an area. Ecosystem Service: Goods and services provided by ecosystems to humans. De-vegetation Leads to Soil Erosion Plants Are Primary Producers Land plants: Dominant primary producers: sunlight  sugar Sugars support all other organisms in terrestrial habitats. Key to the carbon cycle: Reduce CO2, maintain clean air. Plants Provide Humans with Food, Fuel, Fiber, Building Materials, and Medicines Food: – Artificial selection led to dramatic plant changes. Plants Provide Humans with Food, Fuel, Fiber, Building Materials, and Medicines Fuel: – Historically relied on wood burning; fossil fuels replaced wood. Fiber and Building Materials: – Plants provide raw materials. Woody plants: – Lumber, fibers for paper.  Medicines: – About 25% of prescriptions in US each year include at least one molecule derived from plants – Most synthesized by plants to repel herbivores Source Compound Use Cinchona Quinine Malaria prevention Quinidine Heart medication Aspen, willow Salicin Pain relief (aspirin) Wild yams Steroids Precursor compounds for manufacture of birth control pills and cortisone (to treat inflammation) Pacific yew Taxol Treating ovarian cancer Curare vine Tubocurarine Muscle relaxant used in surgery Rosy periwinkle Vinblastine, vincristine Treating leukemia (cancer of blood) 28.2 How Do Biologists Study Green Algae and Land Plants? Analyzing Morphological Traits Green algae include species that are: – Unicellular or multicellular – Colonial – Live in marine, freshwater, or moist terrestrial habitats Majority aquatic green algae, majority land plants terrestrial. Similarities Between Green Algae and Land Plants (1 of 2) Freshwater green algae hypothesized to be closely related to land plants Key traits: Chloroplast structure, thylakoid arrangements, cell walls, sperm, and peroxisomes. Similarities Between Green Algae and Land Plants (2 of 2) Three green algal groups most similar to land plants based on DNA sequence analysis. Largely multicellular and live in freshwater: – Hypothesis: Land plants evolved from green algae that lived in freshwater habitats Major Morphological Differences Among Land Plants (1 of 3) 1. Nonvascular plants: – Nonvascular plants lack vascular tissue, use spores for reproduction (e.g., mosses). Major Morphological Differences Among Land Plants (2 of 3) 2. Seedless vascular plants: – Seedless vascular plants have well- developed vascular tissue, use spores (e.g., ferns). Major Morphological Differences Among Land Plants (3 of 3) 3. Seed plants: – Seed plants have vascular tissue, make seeds (e.g., angiosperms, gymnosperms). Plants 28.3 What Themes Occur in the Diversification of Land Plants? Evolution of land plants: – Evolution of land plants required adaptations for terrestrial life. Transition to Land I: How Did Plants Adapt to Dry Conditions with Intense Sunlight? Once green plants made transition from water, light and carbon dioxide were more plentiful Natural selection favored early land plants with three main types of adaptations: – Early land plants adapted to dry conditions: preventing water loss, UV protection, and water movement. Preventing Water Loss: Cuticle and Stomata Cuticle: watertight sealant; covers aboveground parts – increases survival in dry environments – also keeps CO2 out of plant Stoma: opening surrounded by specialized guard cells Providing Protection from U V Irradiation Plants out of water exposed to harmful UV rays of the sun: – UV light damages DNA by causing thymine dimers – Water absorbs UV light, so algae did not face this problem to the same extent – First plants had UV- absorbing compounds: acted as sunscreen Importance of Upright Growth First land plants kept tissues in contact with moist soil. Intense competition for space and light. Origin of Vascular Tissue Fossils of upright plants contained elongated cells that were organized into tissues along length of plant Biologists hypothesized that these cells were part of water- conducting tissue because some of fossilized cells had: Mapping Evolutionary Changes on the Phylogenetic Tree Cuticle, stomata, and vascular tissue were key adaptations for land colonization. Fundamental adaptations to dry conditions evolved once. Convergent evolution: vessels evolved independently in angiosperms, gnetophytes, and several species of seedless vascular plants Plant Phylogeny - Evolutionary Innovations for Land Transition to Land : How Do Two Plants ReproduceII in Dry Conditions? Life cycles of sexually reproducing eukaryotes serve several functions: – Increasing genetic variability due to meiosis and fertilization – Increasing the number of individuals – Dispersing individuals to new habitats How Do Plants Reproduce in Dry Conditions? Innovations/adaptations were instrumental for efficient plant reproduction on dry land: – Spores resist drying because they are encased in tough coat of sporopollenin – dispersed by wind – Gametes that were produced in complex, multicellular structures – Embryos that were retained on and nourished by parent plant – Embryonic Retention: specialized reproductive organs called gametangia: prevents drying and from physical damage Protective, Complex Reproductive Organs Individuals produce distinctive male and female gametangia: – Antheridium (plural: antheridia): ▪ Sperm-producing – Archegonium (plural: archegonia): ▪ Egg-producing Analogous to the testes and ovaries of animals  Alternation of Generations Alternation of generations: – In coleochaetes, stoneworts, and conjugating algae: ▪ Multicellular form is haploid ▪ Only zygote is diploid All Land Plants Undergo Alternation of Generations Gametophyte-Dominant Life Cycles Evolved Early In nonvascular plants, sporophyte is small and short lived: Largely dependent on gametophyte for nutrition Gametophyte-dominant life cycle Sporophyte-Dominant Life Cycles Evolved Later In ferns and other vascular plants, sporophyte is much larger and longer lived than gametophyte: Sporophyte-dominant life cycle Reduction of Gametophyte Is One of the Strongest Trends in Land Plant Evolution Sporophyte-dominated life cycles were advantageous: Diploid cells can respond to varying environmental conditions more efficiently than haploid cells can Especially true if heterozygous at many Heterospory Pollen grain allows efficient reproduction in some land plants Sperm of nonvascular and seedless vascular plants swim to egg; water must be available Seeded plant sperm rely on pollen to transport sperm thru air in a dry environment for fertilization Seeds Contain an Embryo and a Food Supply with a Protective Coat That Allows Them to Be Dispersed Seed Structure: Heterospory in Gymnosperms: Microspores Produce Pollen Grains; Megaspores Produce Female Gametophytes Flowering Plants or Angiosperms: Most diverse land plants living today (350,000+ species) Success revolves around reproductive organ—the flower: – Stamen contains anther, where microsporangia develop – Carpel > ovary > ovules > megasporangia Flowering Plants Flowers with Different Scents, Shapes, and Colors Attract Different Pollinators Directed-Pollination Hypothesis: Flowers are adaptations to increase probability animal will perform pollination: transfer of pollen from one individual’s stamen to another individual’s carpel Fruits: Structure derived from ovary and encloses one or more seeds Tissues derived from ovary are often nutritious and brightly colored Evolution of flowers made efficient pollination possible Evolution of fruit made efficient seed dispersal possible Plant Phylogeny Emphasizing the Evolutionary Innovations That Allowed Plants to Reproduce Efficiently on Land Angiosperm Radiation Angiosperms divided into two major groups based on morphological traits.: