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BSC 116 Week 3 of notes

by: Ashley Bartolomeo

BSC 116 Week 3 of notes BSC 116

Ashley Bartolomeo
GPA 3.9

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These are notes from lectures 7-9
Principles Biology II
Professor Harris
Class Notes
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This 8 page Class Notes was uploaded by Ashley Bartolomeo on Saturday February 6, 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 30 views. For similar materials see Principles Biology II in Biological Sciences at University of Alabama - Tuscaloosa.

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Date Created: 02/06/16
Lecture 7: Multicellular Eukaryotes – Plants Overview  Plants are photoautotrophs with complex life cycles  Diagnostic traits of land plants  Non­vascular plants = bryophytes  Seedless vascular plants What Is a Plant?  Multicellular, photosynthetic autotrophs (about 290,000 species) o Cell walls of cellulose o Chloroplast with chlorophylls a and b o These traits found among protists as well  Evolved from single­celled, aquatic green algae: charophytes o Supported by morphological/ biochemical evidence  Shapes of cellulose­synthesizing complexes, flagellated sperm  morphology, details of cell division  Sporopollenin: tough outer coating of charophyte zygotes and plants  spores o Supported by molecular phylogenetic analyses  Kingdom Plantae = Embryophytes o Some debate about where to draw the line Plant Life Cycles Are Characterized by Alternation of Generations  Alternation of generations: alternating, multicellular haploid (n) and diploid (2n) phases o Sporophytes (2n) produce spores (n) by meiosis o Spores (n) development into gametophytes (n) o Gametophytes (n) produce gametes (n) by mitosis o Gametes (n) fuse to produce sporophytes (2n)  Dominant phases vary among plant groups Use Living (and Fossil) Plants to Infer Their Pattern of Evolution  Traits of living plants and cladistic methods provide information about the order in which key traits appeared  Fossils (and molecular clocks) help us date clades  Major events in plant evolution o Multicellularity  o Invasion of land (about 475 My) o Origin of vascular tissue (about 520 My) o Appearance of (extant) seed plants (about 305 My)  Each of these events resulted in multiple plant clades  There are various grades of plant morphology Earliest Land Plants Lacked Vascular Tissue  Vascular tissue: specialize cells that transport water, nutrients, etc.  Bryophytes: non­vascular plants o Three phyla:  Heptatophyta (liverworts)  Anthocerophyta (hornworts)  Bryophyta (mosses) o Monophyletic? o Typically form low “carpets” rather than upright branches  Bryophyte life cycles dominated by gametophyte, but with prominent sporophyte Bryophyte Life Cycles Dominated By Gametophyte Stage  Gametophytes (n) develop from spores (n) o Spores germinate to form branched protonemata (1­ cell thick) o Each protonemata produces 1+ gametophores(s) o Anchored by rhizoids: not roots  Gametophytes (n) have either female or male gametangia o Archegonia: produce eggs o Antherida: produce flagellated sperm  Sperm must swim thru water to fertilize eggs o Limits mosses to moist habitats Bryophyte Sporophytes are Dependent on Parental Gametophytes  Sporophytes (2n) grow from embryos in archegonia o Green when young but get nutrition from parental gametophytes  Sporangium (= capsule) on a stalk o Opens via peristome o Releases spores gradually: spread by wind  Haploid spores (n) lead to gametophytes Their Life Cycles and Lack of Vascular Tissue Limit the Diversity of Bryophytes  Bryophytes are small and limited to moist environments  Vascular plants have adaptations to attain a larger size Five Evolutionary Innovations of Vascular Plants  Vascular tissue: xylem to transport water, phloem to transport organic molecules  o Reinforced with lignin: allowed plants to get bigger  Roots: organs to absorb water & nutrients from soil; not merely anchors o Allowed plants to get bigger  Leaves: increase surface area for photosynthesis o Allowed plants to get bigger  Sporophylls: modified leaves bearing sporangia o Many sporangia per plant  Life cycles dominated by sporophytes, with reduction of the gametophytes Seedless Vascular Plant Life Cycles Dominated by Sporophyte Stage  Fern life cycle similar to that of bryophyte o Sporangia organized into sori on the sporophylls  Except that: o The (bisexual) gametophyte stage is much smaller than the sporophyte o The sporophyte is not dependent on the gametophyte Two Extant Phyla of Seedless Vascular Plants  Phylum Lycophyta, 1200 specieis o Club mosses, spike mosses, quillworts o More ancient of the two phyla  Phylum Monilophyta, 12,000 species  o Fern, horsetails, whisk ferns, etc. o More closely related to vascular plants: share derived characters related to leaf  and root growth Ecological Importance of Seedless Vascular Plants  Warmer climate during Paleozoic Era (until about 299 My) o Much more CO2 in atmosphere  Lycophytes and pterophytes highly diverse o Formed first forests o Dense, wet forests o So many plants led to drop in CO2, & global cooling  Cooler, drier climate favored seed plants (305 My)  Remnants of ancient “coal forests” important to our modern economy Lecture 8: Evolution & Diversity of Plants – Part 1 Overview  There has been five key innovations during plant evolution  A few trends are evident in plant evolution o Get bigger with the evolution of vascular tissue o Growth of the sporophyte phase o Shrinkage of the gametophyte phase o Live in a wider range of habitats with the evolution of seeds  Focus on the seed plants – the gymnosperms Five Key Events in the History of Plant Evolution  Key events o Multicellularity o 475 My, invasion of land o 420 My, evolution of vascular tissue o 305 My, appearance of (extant) seed plants o 140 My, evolution of flowers  Grades of plant morphology o Non­vascular bryophytes o Seedless vascular plants o Seed plants o Angiosperms Bryophyte Life Cycles Dominated By Gametophyte Stage  Gametophytes (n) develop from spores (n) o Spores germinate to form branched protonemata (1­ cell thick) o Each protonemata produces 1+ gametophores(s) o Anchored by rhizoids: not roots  Gametophytes (n) have either female or male gametangia o Archegonia: produce eggs o Antherida: produce flagellated sperm  Sperm must swim thru water to fertilize eggs o Limits mosses to moist habitats Seedless Vascular Plant Life Cycles Dominated by Sporophyte Stage  Fern life cycle similar to that of bryophyte o Sporangia organized into sori on the sporophylls  Except that: o The (bisexual) gametophyte stage is much smaller than the sporophyte o The sporophyte is not dependent on the gametophyte Four Evolutionary Innovations of Seed Plants  Further reduction of the gametophyte stage  Variation in spore size o Most seedless plants homosporous o Heterosporous: amle and female spores of different sizes produced by  differentiated gametophytes  Female megaspores produced by megasporangia  Male microspores produced by microsporangia  Seeds: embryo + food supply in protective coat  Ovules and pollen – don’t require a wet environment for contact of gametes What are the Advantages of Seeds?  Seeds are better for dispersal than spores; can remain viable longer o Spores single cells o Seeds multicellular coats with a store of food  Seeds can remain dormant until conditions right for germination  Seeds can get dispersed farther Male Gametophytes = Pollen  Seedless plants: flagellated sperm swim from male gametophyte (antheridium) to female  gametophyte (archegonium)  Seed plants: tiny male gametophyte transported to female gametophyte o Microspore develops into pollen grain: male gametophyte in sporopollenin coat o Pollination: transport by wind or animals (e.g., bees) to female ovule Fertilized Female Ovules Become Seeds  Ovule = megasporangium + megaspore + integument o Integument sporophyte tissue (2n) o Megasporangium sporophyte tissue (2n) o Megaspore develops into female gametophyte (n)  Female gametophyte (n) produces 1+ eggs (n)  Egg (n) fertilized by sperm (n) produced by male gametophyte (n) following pollination o Sperm transported via pollen tube thru the microphyle  Seed: sporophyte embryo (2n) encased in maternal sporophyte tissue Two Major Extant Clades of Seed Plants  Gymnosperms, “naked seeds” on cones o Phylum Cycadophyta, 130 species o Phylum Gnetophyta, 80 species o Phylum Ginkophyta, 1 specie o Phylum Coniferophyta, 600 species  Angiosperms, flowering plants, seeds “contained” in fruits o Phylum Anthophyta  Basal angiosperms (paraphyletic), 100 species: Amborella, water lilies,  etc.  Magnoliids, 8000 species  Monocots, 70,000 species  Eudicots, 170,000 species The Gymnosperm Life Cycle Allows Them to Live in Drier Habitats  Pine tree = mature sporophyte o (male) pollen cones with microsporocytes o (female) ovule cones with megasporocytes  microsporocyte develops into male gametophyte (pollen) that makes sperm  Megasporocyte develops into female gametophyte that makes eggs  Pollinations leads to fertilization o No need for swimming o Seed contains embryo (2n), food reserves (n), maternal seed coat (2n)  Seed germinates to become seedling  Whole life cycle takes 3 years Lecture 9: Evolution & Diversity of Plants – Part 2 Overview  Focus on the seed plants: angiosperms  Angiosperm lifecycle  Plant relationships with animals (including humans)  Structure of vascular plants Angiosperm Evolution  The ancestors of angiosperms and gymnosperms diverged about 305 million years ago o Early angiosperms were likely small­flowered shrubs with simple water­ conducting cells  Angiosperms comprise more than 250,000 living species  Previously, angiosperms were divided into two main groups o Monocots (one cotyledon) o Dicots (two dicots) o DNA studies suggest that dicots are paraphyletic Angiosperms Have Seeds, Flowers and Fruits  Flowers: sex­organs made of up to 4 rings of specialized leaves (sporophylls)  1. Sepals: outer­most ring, usually green  2. Petals: may be brightly colored to attract pollinators (e.g., bees, hummingbirds)  3. Stamens: male flower­parts o Anthers on filaments; produce pollen  4. Carpels: female flower­parts )1+ per flower), produce female gametophytes.  Container in which seeds are enclosed.  Key structure distinguishing angiosperms from  gymnosperms o Sticky stigma binds polled; style connects it to ovary (1+ ovules)  Fruits: mature ovary o Variation in form: fleshy, dry, etc. o Aid in dispersal: can be carried by animals Flower Symmetry  Bilateral symmetry affects the movement of pollinators and reduces gene flow in  diverging populations o Hypothesis – plants with bilateral symmetry may have increased rates of  speciation o This hypothesis can be tested by comparing the number of species in closely  related “bilateral” and “radial” clade The Angiosperm Life Cycle Can Be Highly Specialized  Female gametophyte has large central cell with 2 nuclei (n + n)  Male gametophyte (pollen) has two haploid (n) cells: o 1. Generative cell: divides and forms two sperm o 2. Tube cell: produces a pollen tube  Pollen adheres to the stigma of the carpal, pollen tube rows down within the style of the  carpal.  The tube penetrates through the microphyle, and discharges two sperm cells into  female gametophyte (embryo sac)  Pollen then releases 2 sperm through the tube o One fertilizes embryo (2n) o One fuses with 2 nuclei in central cell: endosperm (3n)  Double fertilization: one fertilization event produces a zygote and the other produces a  triploid cell – unique to angiosperms  Endosperm is the food supply for the seed  Egg and sperm usually from different plants: cross­pollination Animals are Dependent on Plants, and Vice Versa  Herbivory: animals feeding on plants; plants have various adaptations to keep from being eaten o E.g., chemical: caffeine, nicotine, morphine, cyanide o E.g., mechanical: thorns, silica crystals  Many fruits are adapted for animal transport  Plant­pollinator relationships maybe highly specialized o Co­evolution of insects and flowering plants may explain their great diversity Plants Have Many Uses  Food: 80% of our calories come from only 6 angiosperm crops o Wheat, rice, maize (corn), cassaza & sweet potatoes  Food for other human food: plants to feed livestock  Shelter, fuel: wood fibers (clothing), moss for peat  Medicines: in US 25% of prescription drugs contain an active ingredient from seed plants  Spices: derived from a variety of plant parts: flowers (cloves); fruits and seeds (vanilla,  black pepper); leaves (basil, mint), and bark (cinnamon)  Ecosystem function: nutrient cycling o Fix carbon and nitrogen, use excess CO2 Three Levels of Plant Body Organization  Multicellular organisms are more than just a cluster of cells  Various types of cells: differentiated to perform specific functions o Cells for photosynthesis, support, absorption, transport  Tissues: composed of cells within similar form and/or function o Dermal (external), vascular (transport), & ground (other) tissues  Organs: organization of tissues to perform some function; two main systems of vegetative growth  1. Root system: roots  2. Shoot system: stems and leaves o Reproductive growth: e.g., flowers Root System Operates Below Ground  Root function: anchor, absorb minerals & water, store carbohydrates  Two main root morphologies o Taproot: main vertical root from primary root, many lateral roots.  Good for tall  plants o Fibrous roots: no main root; lots of little branches; small plants  Have root hairs: increase surface area for absorption o Extensions of root epithelial (dermal) cells many different kinds of modified roots to serve specialized purposes o Adventitious roots: root tissue emanating from stems or leaves (shoot system) Shoot System Functions Above Ground  Shoot system: reproduction & photosynthesis o 1. Stems o 2. Leaves o 3. Flowers  1. Stems: grow to increase the above­ground volume occupied by branching thus  facilitates dispersal of pollen and fruit; orients the plant in a way that maximizes  photosynthesis o Alternating nodes (where leaves attach) and internodes (stem segments between  nodes) o Primary growth via apical bud, with branches formed by axillary buds o Apical dominance: axillary bud growth inhibited by proximity of apical bud o Stems may be modified for storages, asexual reproduction, etc.  2. Leaves: main organs of photosynthesis o Composed of blade and petiole (stalk) o Veins: vascular tissue of leaves o Simple vs. compound leaves o Conifer needles are leaves o Leaves can be modified for support, protection, etc.  3. Flowers: part of the shoot system, but involved with reproductive growth as opposed to vegetative growth Organs are Composed of Tissues  Plants are made up of three tissue systems: continuous throughout the organ systems of  the plant o 1. Dermal tissue system: external protective covering, first line of defense  Epidermis with a waxy cuticle o 2. Vascular tissue system: internal transport between shoot & root systems;  physical support  Xylem: transports water + minerals from roots up to the shoots  Phloem: transports sugars from where they are made (leaves) to where  they are need (flowers, fruits, roots, etc)  Stele = xylem + phloem; arrangement varies in roots (cylinder) and shoots (bundles) o 3. Ground tissue system: various tissues that are neither vascular nor dermal;  specialized, responsible for metabolic functions  Cortex: between vascular tissue and dermal tissue  Pith: within vascular tissue


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