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` Quic kTime™ and a dec ompres sor are needed to see this pic ture. Get onto land, plants had to evolve a way to keep from drying out and stand upright. Have to be able to transport nutrients, water over long short distances. Plant structures divided into 2 systems: root system (below ground), shoot system (above ground). Systems rely on one another; roots require shoots to photosynthesize. QuickTime™ and a decompressor are needed to see t his picture. Water and mineral salts from soil enter plant through epidermis (outer layer) of roots, cross root cortex, pass into stele (where xylem is), flow up xylem vessels to shoot system. QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . Fig. 36.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Most absorption of water and minerals occurs near root tips, epidermis is permeable to water and root hairs are located. Root hairs allow for maximum uptake. Most plants form partnerships with symbiotic fungi for absorbing water and minerals from soil. Quic kTime™ and a dec ompres sor are needed to see this picture. Water and minerals in root cortex cannot be transported to rest of plant until they enter xylem in stele. Endodermis surrounds stele and is last checkpoint for absorption into vascular tissue. Quic kTime™ and a dec ompres sor are needed to see this pic ture. Some plants have adventitious roots that arise aboveground from stems or even from leaves. Seen in corn - help keep plant upright. Quic kTime™ and a dec ompres sor are needed to see this picture. 1Stems have nodes (leaves attached) internodes (spaces between nodes) Where leaves meet stems are axillary buds - vegetative branch could form. Terminal bud - growth of young shoot is concentrated - growth happens vertically (apical dominance) Quic kTime™ and a dec ompres sor are needed to see this picture. Modified shoots 1Stolons - “runners” of strawberry plants - grow on surface so parent plant can asexually reproduce in large numbers. 2Rhizomes – ginger - horizontal stems that grow underground. QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . Rhizomes 3Tubers – potatoes - swollen ends of rhizomes specialized for food storage. 4Bulbs – onions - vertical, underground shoots consisting mostly of swollen bases of leaves that store food. Tubers Bulbs 2Leaves consist of a flattened blade and a petiole (stalk) Some leaves have evolved other purposes - spines of cacti for defense, leaves modified for water storage, brightly colored leaves that attract pollinators. 3Flowers – discussed later Each organ has 3 tissues: dermal, vascular, and ground. Dermal tissue - epidermis (covers and protects) Epidermis of leaves and most stems secretes waxy coating, cuticle, that helps parts of plant retain water. Land plants - true roots, stems, leaves. Xylem carry water, minerals up from roots - dead at maturity. Phloem - living tissue - distribute sugars, amino acids, other organic products. http://www.bbc.co.uk/schools/gcsebitesize/img/bixylemphloem.gif 2 types of xylem cells: vessel elements, tracheids. Both dead at maturity - help thicken walls to promote water flow. 1Tracheids - long, thin cells with tapered ends. 2Vessel elements - wider, shorter, thinner walled, less tapered than tracheids. 2 types of phloem cells - companion cells and sieve tube members. 1Sieve tube members - tubes that material moves through. 2Companion cells assist sieve tube members. Xylem sap flows into veins of leaf providing them with water. Plants lose water through transpiration (water is replaced through water transport) Xylem sap must rise against gravity through pumping system. Accumulation of minerals in stele lowers water potential, generating positive pressure (root pressure) forces fluid up xylem. Plants rely on osmosis. Direction of water movement depends on solute concentration and physical pressure (water potential) Water moves from high water potential to low water potential. Water potential is measured in MPa, abbreviated psi. Pressure to water can reverse movement of water would normally move. Using syringe (negative pressure) can force water to move upwards. Combined effects of pressure and solute concentrations on water potential: psi = psiP + psis psiP - pressure potential psis - solute potential (or osmotic potential). Flaccid cell, psip = 0. If placed in solution with lower psi, water will leave cell - will plasmolyze, by shrinking and pulling away from wall. As cell begins to swell pushes against wall (turgor pressure) Placed in pure water - cell will have lower water potential due to solutes; water will enter cell. Become turgid (firm) Simple diffusion is not efficient enough. Water and solutes move through xylem vessels and sieve tubes by bulk flow - movement of fluid driven by pressure. Tension allows for transport of materials. Transpiration forces water to move up plant in stream (negative pressure) - allows materials to move in bulk. Larger diameter of stem = faster material can move. Other items regulate water flow. 1Aquaporins - specific transport proteins that aid in passive movement of water. 2Tonoplast (membrane that bounds vacuole), regulates molecular traffic between cytosol and contents of vacuole (cell sap) 3Plasmodesmata (connections between cells) connect symplast (cytoplasm stream) Cell walls of adjacent plant cells apoplast. Leaf epidermis composed of cells tightly locked together. Full of stomata - openings that allow diffusion of carbon dioxide, water vapor, and oxygen between leaf and air. Size of stomata controlled by guard cells open and close opening using turgor pressure. Guard cells open during day to allow CO2 for photosynthesis; close at night to limit loss of water vapor through transpiration (evaporation of water from leaves) Decreased turgor pressure causes guard cells to close (need to conserve water) Absorption of sunlight drives transpiration by causing water to evaporate from mesophyll cells and by maintaining high humidity in air spaces in a leaf. Sunlight drives transport of water. Root pressure causes guttation (oozing of water droplets in morning on tips of grass blades) Roots accumulate water during night, transpiration is low, so water enters leaf at faster rate. Xylem sap pulled through plant creating stream of water that cannot be broken. Cavitation (formation of water vapor pockets in xylem vessel) breaks chain. Occurs when xylem sap freezes in water. Cannot be fixed in trees, but stream can form around it. When transpiration exceeds delivery of water by xylem, (soil begins to dry out) leaves wilt as cells lose turgor pressure. Guard cells control diameter of stomata by changing shape, widening or narrowing gap between the 2 cells. Potassium helps in regulation of guard cells. Their opening is regulated in 3 ways. 1Blue-red wavelengths signal plant to start photosynthesizing. 2Depletion of CO2. 3Internal clock in plant cues plant to start photosynthesizing - started at dawn. Opening and closing cycle of stomata is circadian rhythm, cycles that have intervals of approximately 24 hours. Plants adapted to arid climates (xerophytes) have leaf modifications that reduce rate of transpiration. Some - smaller, thicker leaves. Some shed leaves during extremely dry months. Some - stomata concentrated on lower (shady) leaf surface. Phloem sap Phloem transports organic products of photosynthesis throughout plant via translocation. Phloem sap - aqueous solution sugar, mostly sucrose - is most abundant solute. Xylem - unidirectional movement; phloem movement variable. Sieve tubes carry food from sugar source to sugar sink. Sugar source - plant organ (especially mature leaves) where sugar is being produced by photosynthesis or breakdown of starch. Sugar sink - organ (growing roots, shoots, or fruit) that is net consumer or storer of sugar. Storage organ (like a tuber) can be sink in summer (storing for winter) but source during in beginning of spring http://www.pearsoned.ca/school/science11/biology1 1/sugartransport.html Neither dermal tissue nor vascular tissue. In dicot stems, ground tissue divided into pith, internal to vascular tissue, and cortex, external to the vascular tissue. 3 different types of plant cells: parenchyma, collenchyma, and sclerenchyma. 1Parenchyma cells have walls that are thin and flexible; typical plant cells (sieve-tube members) 2Collenchyma cells - thicker walls than parenchyma cells. Used for support in growing plants. 3Sclerenchyma cells function as supporting elements of plant. Annual plants complete life cycle in single year or less. Biennial plants - two years. Plants that live many years, including trees, shrubs, and some grasses, are perennials. Growth in plants due to embryonic (undifferentiated) cells meristems. Can undergo cell division to produce new organs through life of plant. Elongate and differentiate into cell types depending on tissue of plant. Apical meristems found at tips of roots and stems. Allow for growth in length – only happens at tips of roots and stems. Primary growth – lengthwise, secondary growth - widthwise. Lateral meristems - secondary growth. Root tip protected by root cap to protect meristem. Lateral meristems 2 cambiums responsible for secondary growth. 1Vascular cambium - meristem to produce secondary xylem and secondary phloem. 2Cork cambium - meristem for tough, thick covering for stems and roots replaces epidermis. As secondary growth continues over years, layer upon layer of secondary xylem accumulates, producing wood - actually dead cells. Growth in areas like Maine occur in cycles through dormancy then growth which produce growth rings. Bark - all tissues external to vascular cambium (secondary phloem, cork cambium, and cork) 2 types of secondary phloem: heartwood and sapwood. Heartwood (hardwood) no longer conducts water (responsible for strength in old trees) while sapwood (softwood) functions in transport of water and minerals. 4 groups of land plants: bryophytes, pteridophytes, gymnosperms, and angiosperms. Bryophytes - mosses. Pteridophytes - ferns. Gymnosperms – pines, conifers. Angiosperms - flowering plants. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Bryophytes - offspring remain attached to parent plant. Non-vascular plants. Vascular plants - vascular tissues, cells join into tubes that transport water, nutrients throughout plant body. http://www.science.siu.edu/landplants/Bryophyta/images/Physcomitrium.JPEG Ferns - seedless plants. Seed - plant embryo packaged along with food supply within protective coat. Early seed plants gave rise to diversity of present-day gymnosperms, including conifers. Modern plants angiosperms. http://www.rockhillridge.com/images/hayes/Ferns,%20Hayes%20Tract%206%2003-web.jpg Fern Plant evolution: 1Origin of bryophytes from algal ancestors. 2Origin, diversification of vascular plants. 3Origin of seeds. 4Evolution of flowers. Plants – multicellular, derive energy and nutrition through photosynthesis. Plant cell walls - cellulose. Different from algae - apical meristems, alternation of generations, sporangia that produce walled spores. http://www.botany.hawaii.edu/faculty/webb/BOT311/bot311-00/PlantCellWalls00/CellWallHemiLab.jpg Plants need to grow to maximize absorption. Done through apical meristems undifferentiated cells that divide when needed. Located at tips of roots, shoots. Multicellular plant embryos develop from zygotes - stay in tissues of female parent. Land plants - embryophytes. Parent provides nutrients to embryo. Alternation of generations - gametophyte produces haploid gametes through mitosis that get fertilized (by other gametes); form a diploid zygote that will grow into mature sporophyte. http://fig.cox.miami.edu/~cmallery/150/mitosis/sf9x7c.jpg Sporophyte produces haploid single-celled spores - reproductive cells - grow into gametophyte by mitosis. Size of sporophyte and gametophyte differ in plant species. Bryophytes - gametophyte dominant generation. Pteridophytes, gymnosperms, and angiosperms - sporophyte dominant generation. http://www.sbs.auckland.ac.nz/info/schools/nzplants/images/moss/moss_major_parts1.jpg Spores - covered by sporopollenin – resistant to outside stress. Sporangia found on sporophyte produce spores. Sporopollenin Female gametangium (gamete producing organ) – archegonium produces single egg cell in vase shaped organ. Male gametangia – antheridia produce many sperm cells released to environment. Sperm fuses with egg in archegonium. Female Fusion of sperm and egg Land plants have cuticle – protects from drying out, microbes. Stomata allow exchange of carbon dioxide and oxygen between outside and interior. Plants also produce secondary compounds - alkaloids, tannins, and phenolics such as flavonoids bitter tastes, strong odors, or toxic effects (protection for plant) Some used for medicinal purposes. http://www.naturalproductsmarketplace.com/articles/i461a12.jpg Origin of land plants Chloroplasts of land plants most similar to plastids of green algae. In both - cellulose comprises 2026% of cell wall. http://www.rsbs.anu.edu.au/profiles/Brian_Gunning/Web%20PCB/Ch%2010%20Plastids/Topic%2005%20Chloroplasts-Charophyceae/10%2005%2010.jpg Bryophytes 3 phyla - 1phylum Hepatophyta – liverworts, 2phylum Anthocerophyta – hornworts, 3phylum Bryophyta – mosses. Gametophytes dominant phase of life cycle. Bryophytes anchored by tubular cells or filaments of cells rhizoids. No conducting tissues (xylem, phloem) to distribute water and organic compounds within gametophyte – so very small. http://userwww.sfsu.edu/~biol240/labs/lab_10plantoverview/media/rhizoids.jpg Most mosses lack cuticle, only 1 cell thick – quick absorption from surroundings. Gametophytes produce gametes in gametangia. http://io.uwinnipeg.ca/~simmons/Chap29a98/img016.jpg Bryophyte Reproduction Sperm swim toward archegonia, drawn by chemical attractants. Zygotes and young sporophytes retained and nourished by parent gametophyte. Moss sporophytes have foot, elongated stalk (seta), and sporangium (capsule). Foot gathers nutrients and water from parent gametophyte via transfer cells. Stalk conducts materials to capsule. Capsule – disperse spores. Common in wetlands, wind dispersal allows for inhabiting many different areas. Some moss form deposits of undecayed organic material – peat. Forms peat bogs. Pteridophytes Vascular plants have food transport tissues (phloem) and water conducting tissues (xylem) with lignified cells. 1st vascular plants, pteridophytes, were seedless. http://www.florelaurentienne.com/flore/Groupes/Pteridophytes/images/Adiantum_pedatum_940528_21_800.jpg Seedless Vascular Plants Cooksonia (extinct) - earliest known vascular plant (400 MYA) 2 modern phyla: 1Phylum Lycophyta – lycophytes. 2Phylum Pterophyta -- ferns, whisk ferns, and horsetails. Cooksonia Lycophytes - small leaves (microphylls) with single unbranched vein. Leaves of other vascular plants, megaphylls much larger and highlybranched. Reproduction in Pteridophytes Homosporous (one sex) sporophyte produces a single type of spore. Heterosporous sporophyte (two sexes) produces 2 kinds of spores. Megaspores - females gametophytes. Microspores - male gametophytes. Heterosporous Fig. 29.23 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Modern lycophytes - tropical species that grow on trees as epiphytes, using trees as substrates, not as hosts. Specialized leaves (sporophylls) bear sporangia clustered to form club-shaped cones. http://www.tcr.gov.nl.ca/nfmuseum/images/osmundaclaytoniana3barrdharbourhilljuly122002.jpg Phylum Pterophyta – ferns and relatives. 1Psilophytes - whisk ferns. 2Sphenophytes – horsetails - found in marshy habitats, along streams and sandy roadways. 3Ferns - leaves (fronds) may be divided into many leaflets. Produce clusters of sporangia (sori) on back of green leaves (sporophylls) or on special, nongreen leaves. Dispersed by wind. Sporophylls Sori Seed plants - vascular plants that produce seeds. 3 adaptations that seed plants have: 1Gametophyte more reduced. 2Seed evolved. 3Pollen evolved. Gametophytes of seed plants almost invisible. Gametophytes still exist - plants can destroy themselves at this stage if there something wrong with plant. Seed - sporophyte embryo packaged with food supply within protective coat. Seed plants - 2 different types of sporangia – each produces different spores: megaspores (grows into female gametophyte) and microspores. Gametophytes stay in sporophyte as it develops. Ovule contains integuments (protective covering), megaspore, and megasporangium. Female gametophyte develops inside megaspore; produces 1 + egg cells. Fertilized egg develops into embryo. Whole ovule develops into seed Microspores (pollen) – light, carried through air. Pollen will create pollen tube - allow sperm to travel down into female gametophyte. 2 groups of seed plants: gymnosperms and angiosperms. Gymnosperms 4 phyla of gymnosperms still around. 1Phylum Ginkgophyta - Ginkgo biloba. 2Phylum Cycadophyta - cycads look like palm trees. 3Phylum Gnetophyta – 3 different types of plants including ephedra. Cycad Ephedra Phylum Coniferophyta - largest phyla - includes conifers. Conifer because of reproductive structure (cone) Conifers Conifers - evergreen - keep leaves all year long. Needles help in dry conditions. Conifers - pines, firs, spruces, larches, yews, junipers, cedars, cypresses, and redwoods. Life cycle of gymnosperms Conifers - heterosporous (separate male and female gametophytes) Produce both pollen cones and ovule cones. During pollination, pollen falls on ovule. Pollen creates pollen tube - digests through megaspore. Fertilized megaspore goes through meiosis to produce 4 haploid cells. 1 cell will turn into female gametophyte; other 2 or 3 cells (archegonia) will develop within gametophyte. Angiosperms Angiosperms - flowering plants - produce flowers and fruit. Phylum Anthophyta divided into two groups: monocots and dicots. Most monocots - leaves with parallel veins, dicots - netlike venation. Monocots (grasses) usually have fibrous root systems - look like mat. Dicots (flowers) have taproot system - one large root. Vascular tissue runs length of stem in vascular bundles. Dicots - vascular bundles arranged in a ring; monocots - scattered. Angiosperms - long tracheids that help to transport water and to support plant. Flower specialized for reproduction. Most angiosperms rely on pollination through animals; grasses rely on random chance. Flower - specialized shoot - 4 circles of modified leaves: sepals, petals, stamens, and carpals. 1Sepals - base of flower - modified leaves that enclose flower before it opens. 2Petals lie inside ring of sepals - usually colorful in animal pollinated plants. 3Stamen – male organ - thin, stalk-like filament with sac at top (anther) Anther produces haploid spores that develop into pollen grains. 4Carpal – female organ - contains three parts: stigma, style, ovary. Stigma - sticky top part of flower - extends beyond flower, catches pollen. Style connects stigma to ovary at base of pistil - allows sperm to reach ovules. Ovary - enlarged area at base of pistil that contains one or more ovules. The entire structure is the carpal. An ovule contains the egg nucleus. Fruit - mature ovary. As seeds develop from ovules after fertilization, wall of ovary thickens to form fruit. Fruit helps protect seeds while they disperse. Some fruits, like dandelion, are modified to catch wind. Burrs that stick to animals - fruits. After fertilization, fruit triggered to form. Wall of ovary becomes pericarp (thickened wall of fruit) If flower not pollinated, fruit will not develop. 3 different types of fruits. 1Simple fruits - single ovary, like cherries. 2Aggregate fruit, blackberry - single flower with several carpals. 3Multiple fruit, pineapple - develops a tightly clustered group of flowers. Ovules (develop in ovary) contain female gametophyte (the embryo sac) Angiosperm life cycle starts with mature flower on sporophyte plant, ends with germinating seed. Anther produce microspores - form male gametophytes (pollen). Ovules produce megaspores - form female gametophytes (embryo sacs). Pollen released from anther - carried to sticky stigma of carpal. Plants can self-pollinate; crosspollination is better. Pollen grain begins growing from stigma toward ovary. Discharges 2 sperm cells into female gametophyte. 1 sperm fuses with egg nucleus to form diploid zygote - develops into embryo. Embryo has rudimentary root and 1 (in monocots) or 2 seed leaves (in dicots), (cotyledons) Other sperm nucleus fuses with 2 polar bodies to form endosperm, (triploid or 3n) in monocots. Dicots - nutrition goes directly to cotyledons. As ovules develop into seeds, ovary develops into fruit. Conditions favorable, germination occurs - seed coat ruptures and embryo emerges as seedling. Seedling uses food stored in either endosperm (monocot) or cotyledon (dicot) to start growth. As seed develops, enters dormancy allows it to survive until conditions are favorable. 1st organ to emerge from germinating seed is radicle (embryonic root) Asexual reproduction Plants can clone themselves - vegetative reproduction. Fragmentation - parent plant separates into parts that reform whole plants. Co-evolution Because certain animals only eat certain plants, actually have forced evolution of one another. Plants have evolved special fragrances, that forced evolution of specific animals to pollinate these plants. Plants and human welfare All our fruit and vegetable crops are angiosperms. Corn, rice, wheat, and other grain are grass fruits. Plants for medicinal purposes; more than 25% of our prescriptions come from plants. Destroying these plants may mean destroying possible cures. Biotechnology Selective breeding has allowed humans to spread plants that could not survive for very long (i.e. maize). Scientists use transgenic plants, (genetically engineered to express foreign gene from another species) to study genetics. Hormones Plants produce hormones that regulate growth and development. Hormones - chemical signals produced in one part of body, transported to other parts. Growth towards or away from stimuli (regulated by hormones) - tropism. Growth of shoot towards light - phototropism (positive). Hormone responsible for growth auxin. Quic kTime™ and a dec ompres sor QuickTi me™ and a decompressor are needed to see thisarepicture. needed to see thi s pi ctur e. Auxin produced in large quantities in apical meristem - growth occurs. Auxin used on cut stems to promote root growth. Auxins used as growth inhibitor for some plants - used as pesticides. http://botit.botany.wisc.edu/images/130/Growth_Substances/Auxins/root_formation/ Cytokinins stimulate cytokinesis (cell division) Cytokinins produced in actively growing tissues, particularly roots, embryos, and fruits. Both cytokinins and auxins present, cells divide. Shoots forming with addition of cytokinins http://trilliumresearch.org/images/htr_web_images_research/05_rp_03_30_md.jpg Cytokinin levels raised, shoot buds form. Auxin levels raised, roots form. Cytokinins also slow down aging process of some plant organs florists use sprays to keep flowers fresh. http://www.gbpetalpusher.com/flowers/flower5-big.jpg Gibberellins stimulate growth in leaves and stems - little effect on root growth. Stems, gibberellins stimulate cell elongation and cell division. Gibberellins applied to dwarf plants - grow to normal height. Applied to normal plants - nothing happens. Quic kTime™ and a dec ompres sor are needed to see this pic ture. Many plants - both auxin and gibberellins must be present for fruit to set. Seeds have large amount of gibberellins - signals seed to break dormancy. Abscisic acid promotes plant to become dormant; thought to help leaves drop in fall. Sometimes seed will need to have all abscisic acid removed (through washing) to break dormancy. Also helps to withstand drought sends plant into dormancy until the conditions are favorable again. Ethylene promotes leaf dropping as well as fruit ripening. If fruit producing ethylene placed with fruits that are not, those fruits will also ripen in response to hormone. By losing leaves during fall, plants prevent drying out during winter. Responses to light QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . Plants require light to grow; can absorb various aspects of spectrum of light. Respond differently to different wavelengths of light. 2 different types of plants, short day and long day. Short-day plants - long-night plants -require minimum length of uninterrupted darkness. Long-day plans - short-night plants - require period of continuous darkness interrupted by few minutes of light. Response to light - photoperiodism. Typically, red light used to interrupt nighttime cycle. Tropisms Roots - positive gravitropism (grow in direction of gravity); shoots negative gravitropism (grow against direction of gravity). Thigmotropism - response to touch; in some plants, causes plant to coil around an object (like tendril). QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . Some plants cannot grow in extreme temperatures or salinities; others thrive in them. Freezing of cytoplasm can kill plant because excess ions can accumulate. Quic kT i me™ and a dec om pres s or are needed t o s ee thi s pi c ture. http://www.learnnc.org/lp/media/collections/cede/resized/cedebwr07.jpg Marsh grasses are often tolerate of extreme salinities Plant defenses Plants susceptible to many QuickTi me™ and a decompressor are needed to see thi s pi ctur e. different bacteria and viral infections because of place in food chain. Eaten by herbivores - need protection against excess herbivory – use physical defenses, such as thorns, and chemical defenses, such as production of toxic compounds. http://www.learner.org/jnorth/images/graphics/monarch/PlantDefense01.jpg Some plants able to secrete compounds that kill insect eating it. Most plants resistant to pathogens automatically because they are able to detect infection and kill it off right away. Quick Time™ and a decompressor are needed to s ee this pic ture. http://138.23.152.128/images/leaf.jpg