BSC 116 BSC 116
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This 9 page Class Notes was uploaded by Ashley Bartolomeo on Monday February 22, 2016. The Class Notes belongs to BSC 116 at University of Alabama - Tuscaloosa taught by Professor Harris in Spring 2016. Since its upload, it has received 42 views. For similar materials see Principles Biology II in Biological Sciences at University of Alabama - Tuscaloosa.
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Date Created: 02/22/16
Test Number 2 Lecture 13: Plant Reproduction Overview 3 F’s of the angiosperm life cycle o Flowers o Double fertilization o Fruit Growth and asexual reproduction Flowers are the Reproductive Shoots Flowers: sex organs made up to 4 rings of specialized leaves (sporophylls) o Sepals: outer most ring, usually green o Petals: may be brightly colored to attract pollinators o Stamens: male flower parts Anters on filaments; produce pollen o Carpels: female flower parts Sticky stigma binds pollen; style connects it to ovary Complete flowers vs. incomplete flowers: depends upon complement of organs Single or clusters: inflorescences Gametophytes are Highly Reduced in Seed Plants Anthers have 4 microsporangia = pollen sacs o Microsporocytes (2n) each make 4 microspores (n) o Each microspore divides; generative cell + tube cell + spore wall = pollen grain o Generative cell moves to within tube cell Ovaries have ovules with a megasporangium o Megasporocyte (2n) makes 4 megaspores (n); only one survives o Nucleus of surviving megaspore divides 3x: 8 nuclei; membranes follow (no walls) o This is the female gametophyte = embryo sac Further differentiation of the embryo sac o 3 cells move to the microphyle: egg and 2 synergids o 3 cells move to the other end: antipodal cells o 2 polar nuclei without membranes; in cytoplasm of large central cell Double Fertilization Benefits Parent and the Developing Seed Fertilization beings when pollen grain contacts stigma o Tube cell forms a pollen tube; grows down style Attracted by chemicals from synergids o Generative cell divides into two sperm 1 sperm fertilizes the egg = zygote (2n) Other sperm joins with two polar nuclei = endosperm (3n) o Endosperm provides nutrients for seed o Triggers seed and fruit development Double fertilization benefits seed by creating 3n endosperm for nourishment Double fertilization benefits the parent by not wasting resources on unfertilized eggs Embryonic Development Occurs in the Seed Endosperm develops before embryo o 3n nucleus divides: “milky” multinucleate cell o Development of membranes leads to solid endosperm Zygote becomes embryo o Asymmetrical division into larger basal cell and smaller terminal cell o Basal cell develops into suspensor: anchored in parent Like an umbilicus o Terminal cell develops into the proembryo o Two cotyledons (“seed leaves”) develop; function in storage Monocots have only one cotyledons o Shoots and root apices develop Mature Seeds Are Capable of Long Periods of Dormancy Eudicot seeds vary in cotyledon development o Some (e.g., garden beans) have thick cotyledons, no endosperm Cotyledons full of starch absorbed from endosperm Hypocotyl: lower part, connects to radical (embryonic root) Epicotyl: upper part, with immature leaves (embryonic shoot) o Some (e.g., castor beans) have thin cotyledons, more endosperm Food supply remains in endosperm Monocots have one one cotyledon = scutellum o Coleoptile: sheath surrounding embryonic shoot o Coleorhiza: protects embryonic root Last stage of seed development: ejects most of its water and closes the micropyle o Surrounded by hard seed coat Remains dormant until conditions favorable for germination o Varies from plant to plant: lots of rain, fire, freezing, partial digestion o Seeds can remain viable for decades; “seed bank” At the Appropriate Time, Seeds Germinate Germination begins with uptake of water: imbibition o Causes expansion. Seed coat ruptures o Triggers enzymes to digest & mobilize stored nutrients Eudicots: radical emerges first, followed by hypocotyl o Hypocotyl leads epicotyl and cotyledons o Once above soil, epicotyl expands first leaves; cotyledons die once used up Monocots: coleoptile (protects shoot) leads way up o Shoot grows thru The Flowers Ovaries Become Fruits to Protect and Disperse the Seeds Simultaneous seed and fruit development o Double fertilization triggers hormonal changes: ovary transforms Ovary wall becomes pericarp: thickened wall; other flower parts shed Fruits vary depending upon flower arrangement o Simple fruits: from single (or multiple fused) carpels o Aggregate fruits: from flowers with multiple separate carpels o Multiple fruits: from multiple flowers in an inflorescence; ovary walls fuse o Accessory fruits: incorporate other floral parts besides the ovaries Fruits transport seeds widely during their dormancy o Abiotic: wind & water dispersed o Biotic: lots of fruits are dispersed by animals Plant Animal Interactions Influence Fruit Dispersal & Pollination Many fruits take advantage of animal mobility o Attach externally to disperse seeds o Sweet tasting, nutritious: seeds carried internally Fruits ripen with seeds: so they aren’t eaten too early Animals also disperse pollen, in exchange for nectar o 65% of flowers pollinated by insects o Also by birds & bats Many flowers have very specific pollinators o What hurts the pollinator hurts the plant Asexual Reproduction of Vegetative Shoots Embryonic meristems facilitate asexual reproduction by fragmentation: parent plant severed, leads to two individuals (same genome) Other mechanisms of asexual reproduction o Adventitious shoots: e.g., aspen groves o Apomixes: seeds produced by mitosis; no fertilization: e.g., dandelions Advantages o Don’t need another individual nearby to reproduce o No frail little seedling o Pass on exact genetic info of parent Disadvantage o Pass on exact genetic info of parent “Selfing” is sexual but has the same disadvantage o Many plants with self-incompatibility o Chronologically or physically separate male & female parts Dioecious: one sec or the other Lecture 14: Introduction to Animal Diversity & Early Animal Evolution Overview Animals are the most diverse group of organisms What is an animal?: the key characteristics Brief history of animals Animal body plants o Symmetry o Tissue organization o Body cavities The lowest branches on the animal tree o Phylum Porifera o Phylum Cnidaria Multicellularity Has Arisen More Than Once Multicellular organisms occur in several clades, the dominate three: o Terrestrial plants o Fungi o Animals What is an Animal? Multicellular heterotrophs No cell walls: collagen (protein) for support Many animals have o Muscle cells: contractile cells to do generation motion o Nerve cells: conduct electrical impulses Characteristic reproduction and developmental processes Characteristic Early Development of Animals Asexual reproduction occurs, but it is less common Sexual reproduction typical o Diploid adults produce haploid gametes o Typically with small flagellated sperm and large eggs Zygote develops into gastrula o Cleavage: division without growth o Blastula: hollow ball of cells Internal cavity: blastocoel o Gastrulation: invagination of blastopore to form the beginning of the gut Life Cycles May or May Not Involve Larvae Direct development: offspring looks like a little version of the parent o E.g., mammals, some insects Indirect development: young offspring (larvae) morphologically/ ecologically different than adult o Must go thru metamorphosis o E.g., butterflies, some mollusks Where Did Animals Come From? Animals are opisthokonts like fungi Animals most closely related to colonial choanoflagellate protists o Choanoflagellates similar to choanocytes of sponges Molecular clock dates: o Spilt from fungi: 1000 My o Ancestor of living animals: 675-875 My Earliest large animal fossils: Ediacaran Biota o 550-565 My o Sponges, jellyfish, extinct things? o All marine 575 My old embryos? The Gist of the Last 535 Million Years Paleozoic Era (began 542 My) o Cambrian Explosion: “rapid” appearance in the fossil record of most animal phyla Caused by: increased O2? Change in ecological interactions? o Began in ocean, arthropods (460 My) & vertebrates (360 My) invaded land o Ended with big extinction (End-Permian Extinction) Mesozoic Era (began 251 My): “Age of the Dinosaurs” o Bounce back of animals after extinction Coral reefs: increased diversity of shallow marine habitats First appearance of mammals, birds & flowering plants o End Cretaceous Extinction wiped out dinosaurs & other groups Cenozoic Era (began 65 My): Modern Era o Diversification of large mammals, including humans Animals Have Conserved “Body Plans” Remember plants?: lack specific body plants Animals have more conserved body plans o E.g., mammals always have same number of appendages Animal development under control of Hox genes o Regulate transcription of other genes o Conserved across all animal taxa o But also flexible enough to support evolution of observed diversity Traditionally been interested in three aspects of body plans: symmetry, tissue organization and body cavities o Provide insights into early animal evolution More Advanced Animals Bilaterally Symmetrical Sponges: asymmetrical Sea anemones: radially symmetrical o Many planes with equal halves o No left/ right; just top/ bottom o Typical of sessile of planktonic animals: sit in one place of drift in water Most animal: bilaterally symmetrical o Only one plane produces equal halves o Dorsal, ventral, anterior, posterior o Cephalization: having a front end (head) typical of animals that move under own power Concentration of nervous system/ sense organs where they can do the most good Gastrulation Leads to Embryonic Tissues Sponges lack tissues: cells can de-differentiate into other cell types Radial and bilateral animals go thru gastrulation o Invagination of blastopore, etc. o Archenteron: embryonic gut o Endoderm: tissue lining gut o Ectoderm: outer layer of cells; nervous system Radially symmetrical diploblasts: only two tissue types o Basically a fancy gastrula o E.g., jellyfish, sea anemone Bilateral triploblasts have a third germ layer: mesoderm o Forms all other organs between gut and outer surface: muscles, gonads, circulatory system, etc. o E.g., most other animals Triploblastic Animals Often Have Fluid-Filled Body Cavities Coelom: fluid-filled body cavity Coelomates: body cavity lined with mesoderm Pseudocoelomates: not completely lined with mesoderm o Remnant of embryonic blastocoel Acoelomates: lack a body cavity Fluid filled body cavity serves as a hydrostatic skeleton to antagonize muscles Coelomates have Traditionally Been Called Protostomes or Deuterostomes Coelomates vary in how their coelom forms o Protostomes: solid masses of mesoderm form; expand to filled blastocoel o Deuterostomes: mesoderm buds of endoderm of archenteron Also differences in early zygote cleavage o Protostomes: determinate spiral cleavage o Deuterostomes: indeterminate radial cleavage Also differ in gut development o Protostomes: blastopore becomes the mouth o Deuterostomes: blastopore becomes anus Animal Relationships: Different Views There are some differences o Porifera paraphyletic o Protostomes paraphyletic o Some deuterostomes more closely related to protostomes o Two major groups of protostomes There are points of agreement o Animals monophyletic o Eumetazoa with tissues monophyletic o Most belong to bilateria Major Animal Groups There are five major groups of animal phyla o Parazoa/ Porifera: sponges o Cnidaria: jellyfish, sea anemones, coral o Lophotrochozoa: flatworms, mollusks, segmented worms o Ecdysozoa: arthropods, nematodes o Deuterostomia: echinoderms, chordates These only represent a few animal phyla o There are at least 33 Lecture 15: Introduction to Invertebrates Overview The lowest branches on the animal Tree of Life o Phylum Porifera o Phylum Cnidaria Major Animal Groups There are five major groups of animal phyla o Porifera: sponges; no true tissues, no symmetry o Cnidaria: jellyfish, sea anemones, coral; diploblastic, radial symmetry o Lophotrochozoa: flatworms, mollusks, segmented worms; triploblastic, bilateral symmetry o Ecdysozoa: arthropods, nematodes; triploblastic, bilateral symmetry o Deuterostomia: echinoderms, chordates; triploblastic, bilateral symmetry Phylum Porifera: Sponges Least complex animals: no true tissues Body organized like a perforated vase that water flows thru o Many small holes (ostia) leading to a big open internal space (spongocoel), with a big top opening (osculum) o Spongocoel lined by flagellated collar cells (choanocytes): beat to generate a current o Water flows in ostia and out the osculum Suspension feeders: filter/ capture food particles from the water o Food particles captured by choanocytes No tissues: inner and outer layers of cells, separated by mosphyl o May have hard (calcium carbonate or silica) or firm (sponging, collagen) skeleton o Roving amoebocytes Most sponges hermaphrodites: same individual makes sperms and eggs o Spawn sperm to water, captured in another’s water current o Captured by choanocytes Because sponges lack characteristics of other metazoans, sometimes called Parazoans Phylum Cnidaria: Fancy Gastrulas Radially symmetrical diploblasts No thru-gut: gastrovascular cavity Have stinging cells called cnidocytes o Stinging organelle called a nematocyst No mesoderm, so no true muscles o Just weak contractile cells o Nervous system a diffuse nerve net, “Thus, the animal can detect and respond to stimuli from all directions” Cnidarian Alternation of Generations Alternation of Generations o Not alternation of 2n/n generations (like plants) o Alternation of sexual and asexual generations o Different taxa emphasize different phases Two phases o Medusa: mouth down, swimming, sexual stage o Polyp: mouth up, sedentary, asexual stage Phylum Cnidaria Contains Two Major Clades Medusozoans – all cnidarians that produce a medusa o Class Hydrozoa: alternates between medusa and polyp phases E.g., mostly small things like Obelia o Classes Scyphozoa and Cubozoa: jellyfish and box-jellies Polyp stage small relative to medusa Anthozoa o Class Anthozoa: sea anemones, corals Medusa completely eliminated; only occur as polyps Solitary or colonial