Bio 202 Plants and the Conquest of Land PDF

Bio 202 Plants and the Conquest of Land  Protists: Evolution and Relationships At one time, protists were in a single kingdom However, “protists” is not a monophyletic group Evolutionary understanding is in flux Some relationships are uncertain or disputed...

Bio 202 Plants and the Conquest of Land  Protists: Evolution and Relationships At one time, protists were in a single kingdom However, “protists” is not a monophyletic group Evolutionary understanding is in flux Some relationships are uncertain or disputed New protists still being discovered Classified into supergroups 28.2 Evolution and Relationships  Phagocytosis – the process of one cell engulfing another 28.2 Evolution and Relationships  Endosymbiotic theory Cyanobacterium Food vesicle Primary plastid Feeding groove (a) Primary endosymbiosis During primary endosymbiosis, heterotrophic host cells captured cyanobacterial cells via phagocytosis but did not digest them Endosymbiotic cyanobacteria provided host cells with photosynthetic capacity and other useful biochemical pathways and eventually evolved into primary plastids 28.2 Evolution and Relationships  Evidence for Endoysmbiotic theory -New mitochondria and plastids are formed only through a process similar to binary fission. -In some algae, such as Euglena, the plastids can be destroyed by certain chemicals or prolonged absence of light without otherwise affecting the cell. In such a case, the plastids will not regenerate. -They are surrounded by two or more membranes, and the innermost of these shows differences in composition from the other membranes of the cell. They are composed of a peptidoglycan cell wall characteristic of a bacterial cell. -Both mitochondria and plastids contain DNA that is different from that of the cell nucleus and that is similar to that of bacteria (both in their size and their having a circular form). -DNA sequence analysis and phylogenetic estimates suggest that nuclear DNA contains genes that probably came from plastids. -These organelles' ribosomes (a large complex of RNA and protein which catalyzes protein translation) are like those found in bacteria (70S). https://en.wikipedia.org/wiki/Symbiogenesis# Evidence https://girlmeetsbiochemistry.wordpress.com/ 2013/04/06/endosymbiotic-theory/ 28.2 Evolution and Relationships 28.2 Evolution and Relationships  Ancestry and Diversity of Modern Plants Kingdom Plantae Multicellular eukaryotic organisms composed of cells having plastids Primarily live on land Evolved from green algal ancestors that lived in aquatic habitats Distinguished from modern algal relatives by adaptations to terrestrial life 31.1 Ancestry and Diversity of Modern Plants Figure 31.1 31.1 Ancestry and Diversity of Modern Plants  Charophyceans - protist ancestor with a relatively complex body Filament of cells with side branches Complex charophyceans share several derived traits with land plants Cellulose – constituent of plant cell walls Plasmodesmata – channel through cell wall that allows substances to move between cells (can allow communication and specialization of different tissues) Sexual reproduction using egg and smaller sperm Figure 31.2 31.1 Ancestry and Diversity of Modern Plants  Distinctive feature of land plants Apical meristem – localized regions of cell division (where plants grow) Embryo - a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination. Matrotrophy - zygotes remain sheltered and fed within gametophyte tissue (Embryophytes) Sporopollenin walled spores – tough material that composes much of the walls of plant spores (dry, air resistant reproductive cell ) and helps to prevent cellular damage during transport through the air. Gametangia specialized structures that protect developing gametes (sperm, egg) from drying out and microbial attack Antheridia – round or elongate gametangia producing sperm Archegonia – flask shaped gametangia enclosing an egg Sporangia – structure where spores are produced (bigger diploid sporophyte stage means more spores produced, so we see evolution of larger diploid generations) Alternation of generations - Sporic life cycle 31.1 Ancestry and Diversity of Modern Plants  Figure 31.15a Asexual reproduction by mitosis when conditions are favorable, but a switch to sexual when conditions become unfavorable. Diploid zygote undergoes meiosis to make 4 haploid spores. 31.3 Evolution of Reproductive Features in Land Plants  Alternation of generations – Figure 31.15b two types of multicellular “bodies” that alternate in time Multicellular diploid sporophyte makes haploid spores through meiosis Haploid spores are dispersed and undergo mitosis to make multicellular haploid gametophyte Haploid gametophyte makes gametes (sperm and egg) through mitosis Haploid sperm cell fuses with haploid egg cell to make the diploid zygote Diploid zygote undergoes mitosis to make embryo and ultimately sporophyte 31.3 Evolution of Reproductive Features in Land Plants  The Origin and Evolutionary Importance of the Plant Embryo Charophyceans lack embryos One of the first critical innovations of land plants and defines Embryophytes Plant embryos are young sporophytes that develop from zygotes Three features Multicellular and diploid Zygotes and embryos retained in maternal tissue Depends on organic and mineral materials supplied by mother plant – placental transfer tissues 31.4 The Origin and Evolutionary Importance of the Plant Embryo  Placental transfer tissue Often in gametophyte tissues closest to embryos and in the embryos themselves Cells are specialized to promote the movement of solutes from gametophyte to embryo Finger-like ingrowths of cell wall increase surface area of plasma membrane for transport proteins 31.4 The Origin and Evolutionary Importance of the Plant Embryo  Bryophytes Include liverworts, hornworts, and mosses Each forms a monophyletic phylum Share common structural, reproductive and ecological features 31.1 Ancestry and Diversity of Modern Plants  Figure 31.4 31.1 Ancestry and Diversity of Modern Plants  Figure 31.6 hornwort 31.1 Ancestry and Diversity of Modern Plants  Figure 31.5 31.1 Ancestry and Diversity of Modern Plants  Distinguishing features of bryophytes Gametophytes dominant generation As opposed to dominant sporophyte generation in other plants Sporophytes are dependent on gametophyte – small and short lived. As opposed to independent, large and long-lived in other plants Nonvascular or lacking tissues for structural support and conduction found in other plants (vascular plants) Vascular tissues for structural support and conduction of water, minerals, and nutrients found in other plants (vascular plants) Xylem – conducts water and dissolved nutrients Phloem – conducts sugars and metabolic products Bryophytes Lack true leaves, stems, and roots Rhizoids – structure that functions like a http://www.botany.ubc.ca/bryophyte/stanleypark/sporophyte- root in support or absorption gametophyte2.jpg 31.1 Ancestry and Diversity of Modern Plants  Adaptations to life on land Multicellular diploid sporophyte generation is advantageous because it allows a single plant to disperse widely Uses meiosis to produce numerous, genetically variable haploid spores Each spore has the potential to grow into a gametophyte 31.3 Evolution of Reproductive Features in Land Plants Figure 31.16 31.3 Evolution of Reproductive Features in Land Plants  Figure 31.17 31.3 Evolution of Reproductive Features in Land Plants Figure 31.1 31.1 Ancestry and Diversity of Modern Plants  Lycophytes, ferns and seed-producing plants are vascular plants or tracheophytes Possess tracheids - are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts for water and mineral conduction and structural support Lignin – waterproofing material found in cell walls of tracheids Vascular tissues occur in the major plant organs: stems, roots, and leaves Diverged prior to the origin of seeds Seedless vascular plants http://3.bp.blogspot.com/_b8o0_bDa4QI/RsKvBY5ZufI/AAAAAAAAAF0 /BmCafNOYe6A/s400/xylem1%5B1%5D.gif 24 31.1 Ancestry and Diversity of Modern Plants  Roots, stems and leaves Stems Contain vascular tissue and produce leaves and sporangia Contain phloem and xylem (contains tracheids and lignin) Roots Specialized for uptake of water and minerals from the environment Leaves Photosynthetic function Rhizome - a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes 25 31.1 Ancestry and Diversity of Modern Plants Adaptations That Foster Stable Internal Water Content Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or dis play. Vascular tissue Waxy cuticle present on most surfaces of vascular plant sporophytes Stomate Cutin found in cuticle that helps prevent pathogen Cuticle attack 120 mm (a) Stem showing tracheophyte adaptations Wax prevents dessication Stomata are pores that Stomata open and close to allow gas exchange while minimizing water loss (b) Close-up of stomata a: © The McGraw-Hill Companies, Inc./Linda Graham, photographer; b: © Lee W. Wilcox 26 31.1 Ancestry and Diversity of Modern Plants  Lycophytes and fern Lycophytes – microphyll – only a single unbranched strand of vascular tissue Euphylls (ferns and rest of land plants) – leaves that have multiple veins, usually branching one or more time in leaf 31.1 Ancestry and Diversity of Modern Plants The Origin and Evolutionary Importance of Leaves and Seeds Provides a high surface area that helps leaves to effectively capture sunlight for use in photosynthesis Lycophytes produce simplest, most ancient leaves called lycophylls or microphylls Other vascular plants have leaves with extensively branched veins – euphylls or megaphylls Larger size provide considerable advantage Evolved in a series of steps 31.5 The Origin and Evolutionary Importance of Leaves and Seeds  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Single unbranched leaf vein Branched vascular system (a) L ycophyll (small leaf) (b) Euphyll (large leaf) Fern ancestor had a branched stem system. One branch began to dominate, Branch system formed a flat plane and photosynthetic tissue filled in the spaces Euphyll (c) Euphyll evolution process in pteridophytes 29 31.5 The Origin and Evolutionary Importance of Leaves and Seeds  Life cycle Lycophyte and pteridophyte reproduction is limited by dry conditions, like bryophytes However, if fertilization occurs, lycophytes and pteridophytes can produce many more spores due to their larger sporophyte generation Vascular plant sporophytes are dependent upon maternal gametophytes for only a short time during early embryo development Stems of vascular plant sporophytes are able to produce branches, forming relatively large adult plants with many leaves 31.3 Evolution of Reproductive Features in Land Plants  Figure 31.18 31.3 Evolution of Reproductive Features in Land Plants  Gymnosperms Cycads, ginkgos, and conifers Reproduce using spores and seeds (like angiosperms) Gymnosperms are seed plants Seeds protect and provide energy for young sporophyte “Naked seeds” meaning seeds are not enclosed by fruit 31.1 Ancestry and Diversity of Modern Plants  Angiosperms Distinguished by the presence of flowers and endosperm Flowers are specialized to enhance seed production Fruits develop from flowers and enclose the seed and foster seed dispersal Endosperm is a nutritive seed tissue with increased storage efficiency 31.1 Ancestry and Diversity of Modern Plants  An Evolutionary History of Land Plants A billion years ago, the land surface of the earth was bare Except for some cyanobacteria crusts Origin of land plants essential for Development of substantial soils Evolution of modern plants Animals colonizing land Molecular and fossil data reveal the order plants appeared 31.2 How Land Plants Have Changed the Earth  Three steps to plants conquering land 1. First land plants arise from ancestors shared with aquatic charophycean algae and begin to adapt to terrestrial habitats 2. Seedless plants transform Earth’s ecology 3. Ancient cataclysm led to the diversification of modern angiosperm lineages 31.2 How Land Plants Have Changed the Earth  First plants begin to adapt Land plants inherited some traits from charophycean algae Novel features to adapt to stress of life on land Genes for heat and drought tolerance Also developed Tissue-producing meristems Sporic life cycle Tough-walled spores Sporophyte generation 31.2 How Land Plants Have Changed the Earth  Seedless plants transformed Earth’s ecology Liverworts and mosses produce decay-resistant body tissues Could have begun process of organic carbon burial that helps to reduce amount of greenhouse gas 𝐂𝐎𝟐 in the atmosphere Helped enrich soils Effects on soil, atmospheric chemistry, and climate might have been significant because they could have occurred over large geographic areas and for millions of years before vascular plants became dominant 31.2 How Land Plants Have Changed the Earth  Seedless plants transformed Earth’s ecology continued Modern bryophytes also store CO2 Under cooler than normal conditions, Sphagnum grows more slowly and thus absorbs less CO2 , allowing atmospheric CO2 to rise a bit Since atmospheric CO2 helps to warm Earth’s climate, increasing CO2 warms the climate a little When the climate warms sufficiently, Sphagnum grows faster, thereby sponging up more CO2 as peat deposits Reducing atmospheric CO2 returns the climate to slightly cooler conditions 31.2 How Land Plants Have Changed the Earth  Ecological effects of vascular plants First appear 420-429 mya – Coal Age Carboniferous plants converted huge amounts of atmospheric CO2 into decay-resistant organic material Removal of large amounts of the greenhouse gas CO2 from the atmosphere by plants had a cooling effect on the climate Also became drier because cold air holds less moisture than warm air More fossils are found from early vascular plants due to their abundant lignin and cutin 31.2 How Land Plants Have Changed the Earth  Carboniferous period Extensive forests dominated by tree-sized lycophytes, pteridophytes, and early lignophytes occurred in widespread swampy regions during the warm, moist Carboniferous period (354–290 million years ago) 31.2 How Land Plants Have Changed the Earth  Carboniferous period continued Carboniferous proliferation of vascular plants was correlated with a dramatic decrease in 𝐂𝐎𝟐 in the atmosphere Reached the lowest known levels about 290 million years ago During this period of very low CO2 , atmospheric oxygen levels rose to the highest known levels Seed plants became dominant in the cooler, drier habitats created 31.2 How Land Plants Have Changed the Earth  Figure 31.13 31.2 How Land Plants Have Changed the Earth  Rise of angiosperms Gymnosperms and early angiosperms were probably major sources of food for early mammals as well as herbivorous dinosaurs One day, about 65 mya, at least one large meteorite or comet crashed near Yucatan Peninsula in Mexico 31.2 How Land Plants Have Changed the Earth  Cretaceous-Paleogene (K/T) event K/T event marking end of Cretaceous and beginning of Tertiary Huge amounts of ash, smoke and haze dimmed sunlight long enough to kill many of the world’s plants Dinosaurs were also doomed (with the exception of their descendents – birds) In the aftermath, surviving flowering plants diversified New types of animals also appeared 31.2 How Land Plants Have Changed the Earth