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BIOL 1011
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Plants & The Colonization of Land importance of plants energy – food  energy – fossil fuels  clothing  drugs, medicines  ecosystem functioning  biodiversity features of all plants  plants use starch, not simple sugars (because they absorb water) o amylase: unbranched glucose o amylopectin: branched glucose  chlorophyll b: accessory pigment to chlorophyll a o absorb slightly different wavelengths  cellulose  thylakoid characteristics shared features (synapomorphies) between land plants and charophytes  cell plates form in the center of cell during cell division  plasmodesmata connect plant cells  sperm structure  special enzymes in peroxisomes  rose-shaped cellulose synthesizing complexes features of land plants only  cuticle – a waxy covering to avoid drying out  sporopollenin  multicellular jacketed sex organs – antheridium or archegonium  embryophyte condition  alternation of generations (NOT in charophytes)  o originated when the zygote delays meiosis and undergoes mitosis instead, forming a multicellular diploid o arose independently in evolution several times
 o multicellular haploid plant produces multicellular diploid plant and so on Chlamydomonas (chlorophyta) a single-cell green alga without alternation of generations features important to the conquest of land cuticle  jacketed sex organs  embryo retention  stomates (stomata)  vascular tissue (xylem, phloem)  seed  flower
 Major Groups of Land Plants EMBRYOPHYTA:  10 divisions (phyla) of land plants  4 major groups to focus on: mosses, ferns, conifers, angiosperms mosses (Bryophytes)  low-growing  rudimentary vascular tissues – no true leaves  confined to damp areas because: o no true vascular tissue o sperm can only travel by swimming  gametophyte is dominant and sporophyte is dependent  sporangium is the site of meiosis on the sporophyte  spores fall from the sporangium to the ground and grow into gametophytes  sporophyte dies after producing spores  some mosses have evolved to be able to exist in desert or arctic, i.e. cooksonia moss life cycle:  o spores released from sporangium
 o begin to grow into protonemata
 o buds form and grow into gametophytes (GP)
 o male GP grows sperm in antheridia, while the female GP grows eggs in archegonia
 o sperm swim to archegonia and fertilize the egg o zygote is the sporophyte embryo
 o long stalk of sporophyte grows from the GP
 o capsules are sporangium
 o meiosis in sporangium forms the spores – repeat ferns (Pterophytes) feather shaped leaves  true vascular system  about 10 of 12 thousand species are tropical  sporophytes are dominant  the plant you see is the mature sporophyte  gametophyte withers away after giving rise to sporophyte  o sporangium are in little groups called sorus, on the underside of the sporophyll (leaf) o each sporangium is held together by a ring of cells
 o when right combination of pressure and dryness is reached, the sporangium bursts and the spores are thrown
 o in many species, each sporangia holds 64 spores fern life cycle:
 o spores released from sporangia
 o spores develop into photosynthetic bisexual gametophyte
 o gametophyte produces both sperm and egg at antheridia or archegonia on separate spots on the leaf
 o sperm swims to the egg of other gametophytes
 o sperm fertilizes the egg
 o zygote becomes the sporophyte growing out of the gametophyte o gametophyte withers
 o underside of fern (sprotophyte) has sori (clumps of sporangia) o meiosis occurs in sporangia, forming spores – repeat homospory: one size of spore produced by meiosis heterospory: 2 sizes of spores produced by meiosis microspore that develops into microgametophyte (sperm)  megaspore that develops into megagametophyte (egg) seed plants  evolved pollen and seeds, which mosses and ferns don’t have include: o Gymnosperms (non-flowering seed plants) – 4 phyla
 o Angiosperms (flowering seed plants) – 1 phyla, Anthophyta traits common & exclusive to seed plants seeds  reduced gametophytes – mostly microscopic
 o can develop from spores contained within sporangia, providing protection from things like drought and UV rays  heterospory  o megasporophyll!megasporangia!singular megaspore!singular female gametophyte in ovule o microsporophyll!microsporangia!many microspores!male gametophyte in pollen grain (one per grain) ovules
 o megaspore retained within parent sporophyte o integuments (layers of sporophyte tissue) envelope and protect – one layer in gymnosperms, two layers in angiosperms pollen
 o pollen grains contain male gametophyte
 o protected by a tough coat of sporopollenin
 o pollination: the transfer of pollen to the ovule by wind or animal o if it germinates (begins growing), it gives rise to a pollen tube that discharges two sperm into female gametophyte
 o durable, no flagella, don’t require water or a means of motility evolutionary advantage of seeds: sperm + egg = zygote within the ovule, whole ovule becomes the seed  seed consists of embryo + food supply + protective coat derived from integuments  seeds allow better resistance and easier dispersion  before the evolution of seeds, the only protective state was spores  seeds can remain dormant until they encounter favourable conditions for growth conifers (Coniferophyta)  1 of 4 phyla in Gymnosperms  about 550 species  cones can be male or female o male pine cones: strobili o female pine cones are ovulate  heterosporous  pollen is the mature male gametophyte  megagametophyte (female) nourishes the embryo conifer life cycle
 The pine tree with which we are familiar is the sporophyte. The gametophyte begins at meiosis, when microsporophylls (male cone scales) containing microsporocytes become microspores, and ovules on female cone scales develop megasporocytes that become megaspores. Meiosis produces a tetrad of microspores that develop into a pollen grain which, assisted by a pair of air-filled bladders, become wind- borne to the megagametophyte within an ovule. Meiosis also results in the production of four megaspores, three of which die, leaving a single functional megaspore. Within a pollen grain lies two cells, a generative sperm cell and a tube cell. Pollination occurs when the pollen grain penetrates the micropyle of the female scale. The tube cell elongates into a pollen tube that, over a period of a year or more, eventually reaches the egg cell. The sperm cell migrates through the pollen tube to the egg and fertilization results in the creation of a diploid zygote. The subsequent embryo develops within a naked seed and temporarily suspends development in order to overwinter. Upon receipt of the proper hormonal and environmental cues, germination occurs and a diploid sporophyte, or tree, develops. When the sporophyte is mature, diploid male and female cones emerge, and the alternation of generations completes a cycle.
(from NIFERS/Conifers.htmflowering plants (Anthophyta)  flower is a structure specialized for sexual reproduction  Pollination occurs by animals or sometimes wind monocots: Maize, Wheat, Rice, Bamboo, Orchids, Irises, Lilies, Palms  eudicots: Oaks, Maples, Dandelions, Sunflowers, Legumes, Melons, Potatoes, Poppies, Roses Flowers have up to four kinds of flowers, called floral regions Sepals – Green, Enclose flower before opening (Sterile)  Petals – Aid in attracting pollinators (Sterile)  Stamens – Microsprophylls microspores Pollen/Male Gametophyte, consists of filament and anther (Where pollen is produced)  Carpel – Megasporophytes megaspores Female Gametophyte, o Stigma (Sticky) at tip, style leafs to ovary at the base o Single carpel or group of fused carpel are called Pistil o Floral organs attached to stem at receptacle Angiosperm Life Cycle  Anthers have microsporangia Pollen (containing male gametophytes)  Each grain of pollen has two haploid cells o Generative Cell (Divides into two sperm) o Tube Cell (Produces pollen tube)  Ovule contains female gametophytes/embryo sac, one cell of which is egg. Angiosperm Life cycle - Steps  1. Pollen released from anther, travels to stigma 2. Pollen germinates, becomes mature male gametophyte 3. Male gametophyte extends pollen tube down the style of carpel 4. When ovary is reached, pollen tube penetrates through micropyle (pores in the 
 integument) 5. Two sperm cells released into female embryo sac 6. One sperm fertilizes egg, forms zygote (2N) 7. Other sperm fuses with two nuclei in large central cell of female gametophyte 8. Ovule matures into a seed 9. Zygote develops into sporophyte embryo with rudimentary root + 1-2 Seed 
 leaves called cotyledon. 10. Nucleus of central cell divides repeatedly into endosperm (3N) used for food 
 supply. Steps 6 and 7 above are what is termed “Double Fertilization”  One sperm fertilizes the egg  One sperm fertilizes two polar nuclei Pollen growth (Tomato)  Pollen germinating on stigma  Pollen tube grows toward ovules Angiosperm Ovules and Ovaries  Ovules become seeds  Ovaries become fruits  Fruit Examples with more than 1 Seed
 Watermelon, zucchini, squash, banana, bell pepper, grape, pea pod, apple, orange, tomato
 Fruit Examples with 1 Seed Coconut, Acorn, Grass Grain (Wheat grain, corn kernel), Sunflower Seed, Cherry Megagametophytes!Embryo Sac, usually 8 nuclei and 7 cells Nourishing the Embryo Conifers – Megagametophyte (1N)  Angiosperms – Endosperm (3N) Endosperm is the principal foodstuff of civilization Land Plant Structure Cell Wall  Plant cell walls have both primary and secondary layers, comprised of cellulose microfibrils  Secondary cell walls are stronger and thicker than the primary walls.  Plasmodesmata are the holes between the cell walls of adjacent cells.  Cells use pectin between them to stick together Epidermis  Secretes wax to protect cells  Made of epidermal cells with variety of other functions  Reflective surfaces, slippery edges (Pitcher Plants), Secreting poisons, odors, nectar Parenchyma Cells  Function: Metabolism, storage, photosynthesis  Only have primary cell walls Collenchyma Cells  Function: Support of growing tissues  Only primary cell walls, and they are uneven  Living and flexible at maturity Sclerenchyma Cells  Function: Protection and support  Thick secondary walls causes them to be woody (Lignin)  Can be fibers like burlap, or sclereids like nutshells  Dead at maturity Tracheids and Vessel Elements  Xylem is made up of tracheids and vessel elements  Cells that are involved in particle movement (Sap to move nutrients)  Tracheids are longer and skinnier than vessel elements  Even when dead, these still function  Kills them by apoptosis Sieve Elements  Make up phloem  Function: To move sugar water (photosynthetic) Land Plant Growth  Grows from the tip (vascular plants)  Primary growth is growth in length  Secondary growth is width, and adding wood  Growth occurs only from meristems  Primary growth only occurs from apical meristems (Shoots/Roots)  Secondary growth from lateral meristems 3 Tissue Systems in Plants  Dermal – Epidermis, Variety of Functions  Vascular – Xylem/Phloem, Function: Support/Supply  Ground – Most of volume of young plant, Function: Support because of turgidity Apical Meristems makes 3 more Meristems  1. Protoderm Epidermis 2. Procambium!Vascular tissue 3. Ground Meristem Ground Tissue In Shoots Leaf Primordial – young leaf  Procambium – in the center of stem/shoots  Protoderm – around the outside of plant  Auxillary Bud Meristem – where the new shoots will grow  Ground Meristem – all by procambium and protoderm In Roots  Root Cap – on tip of root, to protect it while pushing through  Stele – In center of root, contains procambium  Zone of Maturation – away from tip, where nothing moves  Zone of Cell Division – Near the tip Differences Between Eudicot and Monocot Roots  In eudicots, xylem is in X-Shape in stele, surround by phloem  In monocots, cylem and phloem in separate bundles in stele, surrounded by pith and pericycle (not in eudicot)  In both, stele surrounded by endodermis, and outside in cortex.  Differences Between Eudicot and Monocot Stems In eudicots, pith is in the center, then ring of vascular bundles with xylem on the inside and phloem on the outside. Then comes the ground tissue/cortex, then epidermis.  In monocots you have vascular bundles randomly throughout ground tissue – but xylem still on inside and phloem on outside. Three types of tree cuts: Tangential, Radial and Transverse. Secondary Growth  Lateral Meristem – circular inside ring, separating primary xylem (inside) + primary phloem (outside) in bundles. (procambium)  Procambium changes into the vascular cambium  Vascular cambium produces secondary xylem to inside, secondary phloem to outside.
 o Fusiform Initial – main type of cell, makes secondary xylem/phloem o Ray Initial – Another type of cell – Make
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