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BSC 116

by: Ashley Bartolomeo
Ashley Bartolomeo
GPA 3.9

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Notes on lectures 13-15
Principles Biology II
Professor Harris
Class Notes
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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


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