BIOL 1030 Exam 1 Study Guide
BIOL 1030 Exam 1 Study Guide BIOL 1030 - 002
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Bio Chapter 26 Sunday, January 31, 2016 8:55 PM Chapter 26: Phylogeny and the Tree of Life Investigating the Tree of Life • Phylogeny -‐-‐ the evolutionary history of a species or group of species • Systematics -‐-‐ a discipline focused on classifying organisms and determining their evolutionary relationships 26.1 Phylogenies show evolutionary relationships • Taxonomy -‐-‐ how organisms are named and classified Binomial Nomenclature • Developed by Carolus Linnaeus • Binomial -‐-‐ two part, Latin, scientific name of an organism o Composed of Genus + specific epithet Hierarchical Classification • From smaller to larger: Genera -‐-‐ families -‐-‐ orders -‐-‐ classes -‐-‐ phyla -‐-‐ kingdoms -‐-‐ domains • Taxon -‐-‐ the named taxonomic unit at any level of the hierarchy Linking Classification and Phylogeny • Phylogenetic tree -‐-‐ branching diagram that represents the evolutionary history of an organism • A phylogenetic tree represents a HYPOTHESIS about evolutionary relationships • Branch points -‐-‐ divergence of two evolutionary lineages from a common ancestor • Sister taxa -‐-‐ groups of organisms that share an immediate common ancestor and are each others closest relatives • Rooted phylogenetic tree -‐-‐ a branch point within the tree represents the most recent common ancestor of all the taxa in the tree • Basal taxon -‐-‐ lineage that diverges early in the history of a group and lies on a branch that originates near the common ancestor • Polytomy -‐-‐ branch point from which more than two descendant groups emerge What We Can and Cannot Learn From Phylogenetic Trees • Trees show patterns of descent, not phenotypic similarity • The sequence of branching in a tree does not necessarily indicate the a ctual ages of the particular species • We should not assume that a taxon on a phylogenetic tree evolved from the taxon next to it Applying Phylogenies • Identifying closely related organisms allows us to establish a "reservoir" of beneficial alleles that can be transferred to cultivated organisms by cross -‐breeding or genetic engineering • Infer species identities by analyzing the relatedness of DNA sequences from different organisms 26.2 Phylogenies are inferred from morphological and molecular data Morphological and Molecular Homologies • Phenotypic and genetic similarities due to shared ancestry = homologies • Organisms that share very similar morphologies or similar DNA sequences are likely to be closely related Sorting Homology from Analogy • Analogy -‐-‐ similarity between organisms due to convergent evolution • Convergent evolution is when similar environmental pressures and natural selection produce similar adaptations in organisms from different evolutionary lineages • Homoplasies -‐-‐ analogous structures that arise independently • The more elements that are similar in two complex structures, the more likely it is that they evolved from a common ancestor Evaluating Molecular Homologies • If species are closely related, their DNA sequences probably differ at o nly one or a few sites 26.3 Shared characters are used to construct phylogenetic trees Cladistics • Cladistics -‐-‐ common ancestry is the primary criterion used to classify organisms • Clades -‐-‐ groups of species that include an ancestral species and all of i ts descendants • Monophyletic -‐-‐ consists of an ancestral species and all of its descendants • Paraphyletic -‐-‐ consists of ancestral species and some, but not all, of its descendants • Polyphyletic -‐-‐ includes distantly related species but does not include the m ost recent common ancestor Shared Ancestral and Shared Derived Characters • Shared ancestral character -‐-‐ a character that originated in an ancestor of the taxon • Shared derived character -‐-‐ an evolutionary novelty unique to a particular clade Inferring Phylogenies Using Derived Characters • Outgroup -‐-‐ a species or group of species from an evolutionary lineage that is known to have diverged before the lineage that includes the species we are studying o A suitable one can be determined based on evidence from morphology, paleontology, embryonic development, and gene sequences • Ingroup -‐-‐ the species we are studying • Derived characters can be determined by comparing members of the ingroup with each other and with the outgroup Phylogenetic Trees with Proportional Branch Lengths • Branch lengths can be drawn to represent the numbers of changes that have taken place in a particular DNA sequence in that lineage • Branch lengths can be proportional to time Maximum Parsimony and Maximum Likelihood • Can never be sure of the most accurate tree for a large data set • Maximum parsimony -‐-‐ we should first investigate the simplest explanation that is consistent with the facts; minimalist approach • Maximum likelihood -‐-‐ identifies the tree most likely to have produced a given set of D NA data, based on certain probability rules about how DNA sequences change over time • When a large amount of data is accurate, these two methods yield similar trees Phylogenetic Trees as Hypotheses • Phylogenetic bracketing allows us to predict that features shared by two groups of closely related organisms are present in their common ancestor and all of its descendants unless independent data indicate otherwise 26.4 An organism's evolutionary history is documented in its genome • DNA sequences show phylogenet ic relationships that cannot be determined by nonmolecular methods Gene Duplications and Gene Families • Gene families -‐-‐ groups of related genes within an organism's genome • Gene duplication increases the number of genes in the genome, providing more opportunities for further evolutionary changes • Orthologous genes -‐-‐ homology is the result of a speciation event and hence occurs between genes found in different species • Paralogous genes -‐-‐ homology results from gene duplication -‐-‐ multiple copies of thes e genes have diverged from one another within a species; more than one copy in the genome Genome Evolution • Lineages that diverged long ago often share many orthologous genes • The number of genes a species has doesn't seem to increase through duplication at the same rate as perceived phenotypic complexity 26.5 Molecular clocks help track evolutionary time Molecular Clocks • Molecular clock -‐-‐ an approach for measuring the absolute time of evolutionary change based on the observation that some genes and other regions of genomes appear to evolve at constant rates o For orthologous genes: assume number of nucleotide substitutions proportional to the time that has elapsed since the genes branched from their common ancestor o For paralogous genes: assume number of sub stitutions proportional to the time since the ancestral gene was duplicated • Not always accurate because: o Some portions of genome have evolved in irregular bursts o Same gene may evolve at different rates in different groups of organisms o The rate of the clock may vary greatly from one gene to another Differences in Clock Speed • If the mutated gene is one critical for survival, the mutation will be unfavorable and gene changes will occur slowly. If the mutated gene is not critical fewer mutations will be harmful and changes will occur more quickly Potential Problems with Molecular Clocks • Natural selection changes direction which can lead to averaging out of changes, allowing this to be an approximate marker of elapsed time • Estimates can be wrong because of the assumption that clocks have been constant for long periods of time • By studying genes of multiple taxa, outliers may average out Applying a Molecular Clock: Dating the Origin of HIV • HIV -‐ 1M first spread to humans around 1910 26.6 Our understanding of the tree of life continues to change based on new data From Two Kingdoms to Three Domains • 3 Domains: Bacteria, Eukarya, and Archaea The Important Role of Horizontal Gene Transfer • Comparisons of complete genomes from the three domains show that there have been substantial movements of genes between organisms in the different domains • Horizontal gene transfer -‐-‐ genes are transferred from one genome to another through mechanisms such as exchange of transposable elements and plasmid, viral infection, and perhaps fusion of organisms Bio Chapter 27 Monday, February 1, 2016 12:27 AM Chapter 27: Bacteria and Archaea Masters of Adaptation • Prokaryotes are the most abundant organisms on earth -‐-‐ can adapt to a broad range of habitats 27.1 Structural and functional adaptations contribute to prokaryotic success • Most prokaryotes are unicellular, typically very small Cell-‐Surface Structures • Cell wall maintains shape, protects cell, prevents from bursting in hypotonic environment • Cell wall contains peptidoglycan -‐-‐ polymer composed of modified sugars cross -‐linked by short polypeptides • Archaeal cell walls contain a variety of polysaccharides and proteins but lack peptidoglycan • Gram stain -‐-‐ categorize bacterial species according to differences in cell wall composition o Gram positive -‐-‐ simpler cell walls with large amount of peptidoglycan o Gram negative -‐-‐ less peptidoglycan and structurally more complex, outer membrane contain lipopolysaccharides • In medicine, gram negative more resistant than gram positive due to outer membr ane • Antibiotics like penicillin inhibit the peptidoglycan cross -‐linking resulting in a nonfunctional cell wall • Capsule -‐-‐ sticky layer of polysaccharide/protein surrounding cell wall that enables prokaryotes to adhere to their substrate or to other individ uals in a colony • Endospore -‐-‐ copy of original cells chromosome surrounded by a tough, multilayered structure; very durable; can remain dormant but viable for centuries • Fimbriae -‐-‐ hairlike appendages that allow prokaryotes to stick to their substrate or o ne another; shorter and more numerous than pili • Pili -‐-‐ appendages that pull two cells together prior to DNA transfer from one cell to the other Motility • Taxis -‐-‐ directed movement toward or away from a stimulus (chemotaxis: response to chemical, phototaxis: light) • Moving toward stimulus is positive taxis, moving away is negative • Flagella = most common form of movement; flagella of the domains made up of different proteins = analogous structures Evolutionary Origins of Bacterial Flagella • Only half of the proteins that comprise the motor, hook, and filament of flagella are necessary. This suggests that the bacterial flagellum evolved as other proteins were added to an ancestral secretory system o Exaptation -‐-‐ the process in which existing structures t ake on new functions through descent with modification Internal Organization of DNA • Less DNA • Most lack compartmentalization • One circular chromosome with fewer proteins • Nucleoid -‐-‐ region of cytoplasm not enclosed by a membrane that contains the chromosome • Plasmids -‐-‐ smaller rings of independently replicating DNA molecules, most carry only a few genes Reproduction • Binary fission -‐-‐ single prokaryotic cell divides into 2 cells • They are small, they reproduce by binary fission, and they often have short genera tion times 27.2 Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes Rapid Reproduction and Mutation • Most genetic variation in sexual populations results from the way existing alleles are arranged in new combinations during meiosis and fertilization • New mutations, through rare on a per gene basis, can increase genetic diversity quickly in a species with short generation times and large populations Genetic Recombination • Genetic recombination -‐-‐ the combining of DNA from two sources • Horizontal gene transfer -‐-‐ transfer of genes between organisms of different species Transformation and Transduction • Transformation -‐-‐ the genotype and possibly phenotype of a prokaryotic cell are altered by the uptake of foreign DNA from its surroundings • Transduction -‐-‐ phages carry prokaryotic genes from one host cell to another Conjugation and Plasmids • Conjugation -‐-‐ DNA is transferred between two prokaryotic cells (usually of the same species) that are temporarily joined • In bacteria, the DNA transfer is always one way • Pilus of donor cell attaches to recipient and retracts, pulling the two cells together. A temporary mating bridge structure forms between the cells and DNA is transferred • F factor -‐-‐ 25 genes required for the produ ction of a pili; (f for fertility) The F Factor as a plasmid + -‐ • F plasmid -‐-‐ cells containing this (F cells) function as DNA donors during conjugation. F are recipients. Condition is transferrable The F factor in the chromosome • A cell with F factor built in to its chromosome is and Hfr cell • Hfr cells act as donor during conjugation with an F cell. DNA enters the cell and homologous -‐ regions of the Hfr and F chromosome may align = segments of DNA are exchanged and recipient becomes recombinant R Plasmids and Antibiotic Resistance • R-‐plasmids -‐-‐ carry "resistance genes" which code for enzymes that specifically destroy or otherwise hinder the effectiveness of certain antibiotics 27.3 Diverse nutritional and metabolic adaptations have evolved in prokaryotes • Phototrophs obtain energy from light • Chemotrophs obtain energy from chemicals • Autotrophs need only a carbon source • Heterotrophs require at least one organic nutrient to make other organic compounds The Role of Oxygen in Metabolism • Obligate aerobes -‐-‐ must use oxygen for cellular respiration and cannot grow without it • Obligate anaerobes -‐-‐ are poisoned by oxygen; some live exclusively by fermentation, others use anaerobic respiration • Anaerobic respiration -‐-‐ extract chemical energy using substances other than oxygen • Facultative anaerobes -‐-‐ use oxygen if it is present but can also carry out fermentation or anaerobic respiration in an anaerobic environment Nitrogen Metabolism • Nitrogen is essential for produ ction of amino acids and nucleic acids in all organisms • Nitrogen fixation -‐-‐ conversion of atmospheric nitrogen to ammonia • Nitrogen fixing prokaryotes can increase the nitrogen available to plants Metabolic Cooperation • Oxygen inactivates the enzymes involv ed in nitrogen fixation so one cell cannot do both at the same time • Heterocysts -‐-‐ cells that carry out only nitrogen fixation; surrounded by a thick cell wall that prevents the entry of oxygen • Biofilms -‐-‐ surface-‐coating colonies. Cells in biofilms secrete signaling molecules that recruit nearby cells, causing the colonies to grow and produce polysaccharides and proteins that stick the cells to the substrate 27.4 Prokaryotes have radiated into a diverse set of lineages An Overview of Prokaryotic Diversity • Metagenomics -‐-‐ obtaining genetic genomes from environmental samples • Due to horizontal gene transfer, significant portions of the genomes of many prokaryotes are mosaics of genes imported from other s pecies Bacteria • Includes every major mode of nutrition and metabolism Archaea • Extremophiles -‐-‐ live in extreme conditions • Extreme halophiles -‐-‐ live in highly salty environments • Extreme thermophiles -‐-‐ thrive in very hot environments • Methanogens -‐-‐ archaea that release methane as a by-‐product of their unique ways of obtaining energy 27.5 Prokaryotes play crucial roles in the biosphere Chemical Recycling • Decomposers -‐-‐ breakdown dead organisms as well as waste products and thereby unlock supplies of carbon, nitrogen, and other elements • Prokaryotes can convert some molecules to forms that can be taken up by other organisms Ecological Interactions • Symbiosis -‐-‐ an ecological relationship in which two species live in close contact with each other • Host -‐-‐ the larger organism in a symbiotic relationship • Symbiont-‐-‐ the smaller organism in a symbiotic relationship • Mutualism -‐-‐ interaction in which both species benefit • Commensalism -‐-‐ one species benefits while the other is neither harmed nor benefitted • Parasitism -‐-‐ ecological relationship in which a parasite eats the cell contents, tissues, or body fluids of its host • Pathogens -‐-‐ parasites that cause disease 27.6 Prokaryotes have both beneficial and harmful impacts of humans Mutualistic Bacteria • Bacteria aid human digestion and immunity Pathogenic Bacteria • Exotoxins -‐-‐ proteins secreted by certain bacteria and other organisms • Endotoxins -‐-‐ lipopolysaccharide components of the outer membrane of gram -‐negative bacteria; released only when the bacteria die and their cell walls break down Bio Chapter 28 Monday, February 1, 2016 12:29 AM Chapter 28: Protists Living Small • Protists -‐-‐ mostly unicellular eukaryotes 28.1 Most eukaryotes a single-‐celled organisms • Eukaryotes have membrane bound organelles • Eukaryotes have a well developed cytoskeleton that provides structural support, enabling cells to have asymmetrical form, change shape as the feed, move, or grow Structural and Functional Diversity in Protists • Most protists are unicellular but some are colonial and multicellular • Cellular functions carried out by subcellular organelles • Heterotrophs, photoautotrophs, and mixotrophs • Mixotrophs -‐-‐ combine photosynthesis and heterotrophic nutrition • All three sexual lifecycles • Ongoing changes in our understanding of phylogeny in protists Endosymbiosis in Eukaryotic Evolution • Endosymbiosis -‐-‐ a relationship between two species in which one organism lives inside the cell or cells of another organism • Mitochondria arose from an alpha proteobacterium which was engulfed by an archaeal cell that may have evolved to have eukaryotic features Plastid Evolution: A Closer Look • Heterotrophic eukaryote acquired an additional endosymbiont -‐-‐ a photosynthetic cyanobacterium -‐-‐ that then evolved into plastids = two lineages of photosynthetic protists (algae): red algae and green algae • Algae have a double membrane with transport proteins • Secondary endosymbiosis -‐-‐ algae were ingested in the food vacuoles of heterotrophic eukaryotes and became endosymbionts themselves 28.2 Excavates include protists with modified mitochondria and protists with unique flagella • Excavata -‐-‐ based on morphological studies of the cytoskeleton; some members have an "excavated" feeding groove on one side of the cell body o Ex. Diplomonads, parabasalids, and euglenozoans Diplomonads and Parabasalids • Lack plastids • Highly modified mitochondiria • Most are anaerobic • Diplomonads -‐-‐ have reduced mitochondria called mitosomes, lack functional electron transport chains o Ex. Giardia intestinalis • Parabasalids -‐-‐ have reduced mitochondria called hydrogenosomes, anaerobic -‐ release Hydrogen as a by-‐product o Ex. Trichomonas vaginalis Euglenozoans • Euglenozoans -‐-‐ includes predatory heterotrophs, photosynthetic autotrophs, mixotrophs, and parasites; main feature: a rod with either a spiral or a crystalline structure inside each of their flagella Kinetoplastids • Kineotoplastids -‐-‐ have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast • Feed on prokaryotes in freshwater, marine, and moist terrestrial ecosystems, species that parasitize animals, plants, and other protists o Ex. Trypanosoma -‐-‐ sleeping sickness Euglenids • Euglenid -‐-‐ has a pocket at one end of the cell from which one or two flagella emerge • Some are mixotrophs, others e ngulf prey by phagocytosis 28.3 The "SAR" clade is a highly diverse group of protists defined by DNA similarities • Based on whole-‐genome DNA sequences; includes stramenopiles, alveolates, and rhizarians • Stramenopiles and alveolates originated through seco ndary endosymbiosis Stramenopiles • Stramenopiles -‐-‐ photosynthetic; characteristic flagellum has numerous fine hairlike projections paired with a shorter, smooth flagellum Diatoms • Diatoms -‐-‐ unicellular algae with glass -‐like wall made of silicon dioxide embedded in an organic matrix that provides protection from being crushed by predators • Very abundant (evidence in diatomaceous earth of the fossil layer) • During blooms, experience rapid population growth due to ample nutrients being available; they living ones sink to the bottom and pump carbon to the ocean floor Golden Algae • Golden algae -‐-‐ color due to yellow and brown carotenoids; biflagellated cells • freshwater • All are photosynthetic, some are mixotrophs that use phagocytosis • Most are unicellular Brown Algae • Brown algae -‐-‐ largest and most complex; all multicellular; most marine • Rootlike holdfast anchors the algae and stemlike stipe, which supports the leaflike blades • Adaptations that allow their main photosynthetic surfaces to be near the surface of the water Alternation of Generations • Alternation of generations -‐-‐ alternation of multicellular haploid and diploid forms • Diploid sporophyte produces haploid spores (zoospores) that move by flagella • Zoospores develop into haploid multicellular gametophytes wh ich produce gametes • Union of two gametes (fertilization) results in a diploid zygote which grows and becomes a multicellular sporophyte • Heteromorphic -‐-‐ sporophytes and gametophytes are structurally different • Isomorphic -‐-‐ sporophytes and gametophytes look similar to each other although they differ in chromosome number Alveolates • Alveolates -‐-‐ have membrane enclosed sacs (alveoli) just under the plasma membrane Dinoflagellates • Dinoflagellates -‐-‐ cells reinforced by cellulose plates • Two flagella located in g rooves in the cellulose plates make them spin as they move • Some are purely heterotrophic, others are photosynthetic ( phytoplankton), or mixotrophs • During a bloom, create red tide that turns the water red and produce toxins that kill fish Apicomplexans • Apicomplexans -‐-‐ almost all are parasites of animals that spread through host as tiny, infectious cells called sporozoites • Apex of cell contains complex of organelles for penetrating host tissues and cells • Not photosynthetic but some have a modified plasti d • Complex lifecycle requiring 2+ hosts (ex. Plasmodium -‐-‐ malaria) Ciliates • Ciliates -‐-‐ named for use of cilia to move and feed • Most are predators • Have two types of nuclei: tiny micronuclei and large macronuclei • Conjugation -‐-‐ a sexual process in which two individuals exchange haploid micronuclei but do not reproduce = genetic diversity • Reproduce asexually through binary fission • Genes in macronucleus control functions of cell Rhizarians • Amoebas -‐-‐ move and feed through pseudopodia (extensions that extend and are anchored, then cytoplasm streams into it = movement) Radiolarians • Radiolarians -‐-‐ have delicate, symmetrical internal skeletons made of silica • Mostly marine • Psuedopodia radiate from central body • Engulfs smaller microorganisms that become attached to the pseudopodia Forams • Foraminiferans -‐-‐ porous shell called tests made of single piece of organic material hardened by calcium carbonate • Marine and freshwater Cercozoams • Cercozoams -‐-‐ ameboid and flagellated protists that feed using threadlike pseudopodia • Marine, freshwater, and soil • Most are heterotrophs 28.4 red algae and green algae are the closest relatives of land plants • Archaeplastida -‐-‐ monophyletic group including red algae, green algae, and land plants. o Descended from ancient protist that engul fed cyanobacterium Red Algae • Red algae -‐-‐ red due to photosynthetic pigment phycoerythrin • Most are multicellular • Sexual reproduction -‐-‐ commonly have alternation of generations • Don’t have flagellated gametes -‐-‐ water currents bring gametes together Green Algae • Green algae -‐-‐ chloroplasts very similar to plants' • Divided into two groups -‐-‐ charophytes and chlorophytes • Charophytes most closely related to land plants • Chlorophytes -‐-‐ larger size and greater complexity because o Formation of colonies o Formation of true multicellular bodies by cell division and differentiation o Repeated division of nuclei with no cytoplasmic vision 28.5 Unikonts include protists that are closely related to fungi and animals • Unikonta -‐-‐ includes animals, fungi, and some protists Amoebozoans • Amoebozoans -‐-‐ includes many species of amoeba that have lobe or tube shaped pseudopodia rather than threadlike pseudopodia Slime Molds • Produce fruiting bodies that aid in spore dispersal • Plasmodial slime molds o Brightly olored o Form a mass called plasmodium o Unicellular mass of cytoplasm that is undivided by plasma membranes and contains many nuclei -‐-‐ "supercell" due to mitosis not followed by cytokinesis o Plasmodium extends pseudopodia to engulf food particles by phagocytosis -‐-‐ if habitat dries up it differentiates into fruiting bodies for sexual reproduction • Cellular slime molds o When food is depleted cells aggregate but remain separated by their plasma membranes -‐-‐ form an asexual fruiting body o Cells forming stalk dry up but spores cells at top sur vive -‐-‐ some cells have mutated so they never go to the stalk but the stalk cells wont reproduce with them Tubulinids • Lobe or tube shaped pseuodopodia • Unicellular • Most are heterotrophs Entamoebas • Parasites • E. histolytica is only pathogenic one -‐-‐ causes dysentery Opisthokonts • Opisthokonts -‐-‐ animals, fungi, and several groups of protists 28.6 Protists play key roles in ecological communities • Most are aquatic Symbiotic Protists • Dinoflagellates are food providing symbiontic partners of coral polyps which build coral reefs • Protists in gut of termites that allow them to digest wood Photosynthetic Protists • Producers -‐-‐ organisms that use energy from light (or inorganic chemicals) to convert carbon dioxide to organic compounds Bio Chapter 29 Monday, February 1, 2016 12:29 AM Chapter 29: Plant Diversity I: How Plants Colonized Land The Greening of Earth • Plants supply oxygen and food to terrestrial animals and create habitats for organisms by stabilizing the soil 29.1 Land plants evolved from green algae Morphological and Molecular Evidence • Plants are multicellular, eukaryotic, photosynthetic autotrophs • Plants have cell wall made of cellulose • Have chloroplasts with chlorophyll a and b • Similar to charophytes o Rings of cellulose-‐synthesizing proteins in the plasma membrane o Structure of flagellated sperm o Formation of a phragmoplast (a group of microtubules between daughter nuclei of dividing cells) Adaptations Enabling the Move to Land • Sporopollenin -‐-‐ layer of durable polymer in charophytes that prevents exposed zygotes from drying out o Allow plants to grow out of water Derived Traits of Plants • Alternation of generations • Multicellular, dependent embryos • Walled spores produced in sporangia (produces the spores) • Multicellular gametangia (where gametes are produced) • Apical Meristems (produces cells that protect the plant) • Cuticle -‐-‐ covering of wax and other polymers that acts as waterproofing to prevent excess water loss and protecting against microbial attack • Stomata -‐-‐ pores that allow the exchange of carbon dioxide and oxygen between the outside air and the plant The Origin and Diversification of Plants • Vascular tissue -‐-‐ cells joining into tubes that transport water and nutrients throughout the plant = vascular plants • Nonvascular plants often informally called bryophytes • Lycophytes -‐-‐ club mosses and their realtives; seedless vascular • Monilophytes -‐-‐ ferns and their relatives; seedless vascular • Grade -‐-‐ group of organisms that share key biological features; don’t necessarily share the same ancestry • Seed -‐-‐ embryo packaged with a supply of nutrients inside a protective coat • Gymnosperms -‐-‐ "naked seed" plants; seeds are not enclosed in chambers; conifers • Angiosperms -‐-‐ all flowering plants; seeds develop inside chambers that originate within flowers 29.2 Mosses and other nonvascular plants have life cycles dominated by gametophytes • Liverworts -‐-‐ phylum Hepatophyta • Mosses -‐-‐ phylum Bryophyta • Hornwarts -‐-‐ phylum Anthocerophyta • Earliest lineages to have diverged from the common ancestor of land plants Bryophyte Gametophytes • Haploid gametophytes are the dominant stage of the life cycle • Protonema -‐-‐ mass of green, branched, once -‐cell-‐thick filaments • Protonema produces buds which has an apical meristem that generates gametophores (gamete producing structure) • A protonema + a gametophore = the body of a moss gametophyte • Rhizoids -‐-‐ long, tubular single cells (liverworts and hornworts) or filaments of cells (mosses) that anchor the gametophytes • Gametangia -‐-‐ formed by gametophytes; produces gametes and is covered with protective tissue o Archegonium -‐-‐ produce one egg o Antheridium -‐-‐ produce one sperm • Bryophyte sperm need water to get to the egg = most live in moist environment • Many bryophytes can increase the number of individuals in a local area through various methods of asexual reproduction Bryophyte Sporophytes • Cells contain plastids that are green and photosynthetic • Cannot live independently -‐-‐ attached to and dependent on gametophyte for sugars, amino acids, minerals, and water • Smallest of all plant sporophytes • Consist of a foot, a seta, a nd a sporangium o Foot -‐-‐ embedded in the archegonium, absorbs nutrients from the gametophytes o Seta -‐-‐ stalk, conducts these materials to the sporangium o Sporangium/Capsule -‐-‐ uses materials to produce spores by meiosis • Peristome -‐-‐ ring of interlocking tooth-‐like structure found on the upper part of the capsule. Open under dry conditions, close under moist. Allow spores to be gradually discharged into the wind • Moss and hornwort sporophytes larger and more complex than liverwort The Ecological and Economic Importance of Mosses • Help retain nitrogen in bare sandy soil • Harbor nitrogen fixing cyanobacteria increasing nitrogen availability • absorb damaging levels of UV in deserts or higher altitudes • Peat -‐-‐ partially decayed organic material o Can be used as fuel o Can preserve corpses o Carbon reservoirs stabilize atmospheric CO concent2ations 29.3 Ferns and other seedless vascular plants were the first plants to grow tall Origins and Traits of Vascular Plants • Branched sporophytes not dependent on gametophytes for nutrition • Main traits that characterize living vascular plants: life cycles with dominant sporophytes, transport in vascular tissues called Xylem and phloem, and well -‐developed roots and leaves, including spore-‐bearing leaves called sporophylls Life Cycles with Dominant Sporophytes • Sporophytes are larger and more complex than gametophytes Transport in Xylem and Phloem • Xylem: conducts most of the water and minerals • Tracheids -‐-‐ tube shaped cells in the xylem that carry water and minerals up from the roots • Lignin -‐-‐ polymer that strenthens the cell walls of water -‐conducting cells in vascular plants • Phloem -‐-‐ tissue that has cells arranged into tubes that distribute sugars, amino acids, and other organic products • Lignin helped plants grow taller • Taller plants outcompete shorter one for sunlight and their spores disperse farther Evolution of Roots • Roots -‐-‐ organs that absorb water and nutrient from the soil & anchor vascular plants • May have evolved from lower portion of the stem Evolution of Leaves • Leaves -‐-‐ increase the surface area of the plant body and are the primary photosynthetic organ of vascular plants o Microphylls -‐-‐ small spine-‐shaped leaves supported by a single strand of vascular tissure; lycophytes only o Megaphylss -‐-‐ leaves with highly branched vascular system Sporophylls and Spore Variations • Sporophylls -‐-‐ modified leaves that bear sporangia • Sori -‐-‐ clusters of sporangia produced by fern sporophylls • Strobili -‐-‐ groups of sporophylls forming a cone-‐like structure in many lycophytes and most gymnosperms • Homosporous -‐-‐ one type of sporangium that produces one type of spore that typically grows into a bisexual gametophyte; most seedless vascular plant species • Heterosporous -‐-‐ has two types of sporangia and produces two kinds of spores • Megaspores -‐-‐ develop into female gametophytes; produced by megasporangia on megasporophylls • Microspores -‐-‐ develop into male gametophytes Classification of Seedless Vascular Plants Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts • Most ancient group of vascular plants Phylum Monilophyta: Ferns, Horsetails, and Whisk Ferns and Relatives • Most widespread seedless, vascular plants • Megaphyll leaves and roots that can branch at various points • Equisetum = horsetails; found in marshy places and along streams • Psilotum and Tmesipteris = whiskferns; only vascular plants lacking true roots The Significance of Seedless Vascular Plants • Contributed to large reduction in carbon dioxide levels during the carbonifero us period • Seedless vascular plants forming the first forests eventually became coal
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