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Plants The Important parts. Basic Vocab you need to know! • seed - an embryo and nutrients surrounded by a protective coat • Megasporangia produce megaspores that give rise to female gametophytes • Microsporangia produce microspores that give rise to male gametophytes and develop into pollen Common in all seed plants – Reduced gametophytes – Heterospory = magasporangia make female gametophytes and microsporangia make male gametophytes – Ovules – Pollen • Seeds provide some evolutionary advantages over spores: – They may remain dormant for days to years, until conditions are favorable for germination – They may be transported long distances by wind or animals • Pollination is the transfer of pollen to the part of a seed plant containing the ovules • In what ways could pollen be dispersed? Fig. 30-3-2 Female gametophyte (n) Spore wall Egg nucleus (n) Male gametophyte (within a germinated pollen grain) (n) Micropyle (b) Fertilized ovule Discharged sperm nucleus (n) Pollen grain (n) • A flower is a specialized shoot with up to four types of modified leaves: Flowers – Sepals, which enclose the flower – Petals, which are brightly colored and attract pollinators – Stamens, which produce pollen on their terminal anthers – Carpels, which produce ovules •A carpel consists of an ovary at the base and a style leading up to a stigma, where pollen is received Fig. 30-7 Stigma Stamen Anther Carpel Style Filament Ovary Petal Sepal Draw and label this in your notes! You will need to know this! Ovule Fruit AKA Ovaries • A fruit typically consists of a mature ovary but can also include other flower parts • Fruits protect seeds and aid in their dispersal Fig. 30-8 Tomato Ruby grapefruit Nectarine What are the various methods in which seeds can be dispersed? Hazelnut Milkweed Fig. 30-9 Wings Seeds within berries Barbs Angiosperm Diversity • Cotyledon - seed leaves (found within a seed, the embryo consists of a root and two cotyledons) • The two main groups of angiosperms are monocots (one cotyledon) and eudicots (“true” dicots) AKA dicots • The clade eudicot includes some groups formerly assigned to the paraphyletic dicot (two cotyledons) group Fig. 30-13n Monocot Characteristics You will need to know these characteristi cs from this and the next slide! Eudicot Characteristics Embryos Two cotyledons One cotyledon Leaf venation Veins usually parallel Veins usually netlike Stems Vascular tissue scattered Vascular tissue usually arranged in ring Fig. 30-13o Monocot Characteristics Eudicot Characteristics Roots Taproot (main root) usually present Root system usually fibrous (no main root) Pollen Pollen grain with one opening Pollen grain with three openings Flowers Floral organs usually in multiples of three Floral organs usually in multiples of four or five Systems • Roots are multicellular organs with important functions: – Anchoring the plant – Absorbing minerals and water – Storing organic nutrients • taproot system consists of one main vertical root that gives rise to lateral roots, or branch roots Fig. 35-4 Prop roots “Strangling” aerial roots Storage roots Buttress roots Pneumatophores • A stem is an organ consisting of – An alternating system of nodes, the points at which leaves are attached – Internodes, the stem segments between nodes • An axillary bud is a structure that has the potential to form a lateral shoot, or branch • An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot • Apical dominance helps to maintain dormancy in most nonapical buds Fig. 35-2 Reproductive shoot (flower) Apical bud Node Internode Apical bud Vegetative shoot Leaf Shoot system Blade Petiole Axillary bud Stem Taproot Lateral branch roots Root system • The leaf is the main photosynthetic organ of most vascular plants • Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem • Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves – Most monocots have parallel veins – Most eudicots have branching veins Fig. 35-6 (a) Simple leaf Petiole Axillary bud Leaflet (b) Compound leaf Petiole Axillary bud (c) Doubly compound leaf Leaflet Petiole Axillary bud • Lateral meristems add thickness to woody plants, a process called secondary growth • There are two lateral meristems: the vascular cambium and the cork cambium • The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem • The cork cambium replaces the epidermis with periderm, which is thicker and tougher Fig. 35-11 Primary growth in stems Epidermis Cortex Shoot tip (shoot apical meristem and young leaves) Primary phloem Primary xylem Pith Lateral meristems: Vascular cambium Cork cambium Secondary growth in stems Periderm Axillary bud meristem Cork cambium Cortex Root apical meristems Pith Primary xylem Secondary xylem Vascular cambium Primary phloem Secondary phloem Primary Growth of Roots • The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil • Growth occurs just behind the root tip, in three zones of cells: – Zone of cell division – Zone of elongation – Zone of maturation Video: Root Growth in a Radish Seed (Time Lapse) Fig. 35-13 Cortex Vascular cylinder Epidermis Key to labels Dermal Root hair Zone of differentiation Ground Vascular Zone of elongation Apical meristem Root cap 100 µm Zone of cell division Fig. 35-14a2 (a) Root with xylem and phloem in the center (typical of eudicots) Endodermis Key to labels Pericycle Dermal Ground Vascular Xylem Phloem 50 µm Fig. 35-14b Epidermis Cortex Endodermis Key to labels Vascular cylinder Pericycle Dermal Ground Vascular Core of parenchyma cells Xylem Phloem 100 µm (b) Root with parenchyma in the center (typical of monocots) Response in Plants Water Pressure and Osmosis • Water potential is a measurement that combines the effects of solute concentration and pressure • Water potential determines the direction of movement of water • Water flows from regions of higher water potential to regions of lower water potential – this sounds familiar!!! OSMOSIS!!!! • Water potential is abbreviated as Ψ and measured in units of pressure called megapascals (MPa) • Ψ = 0 MPa for pure water at sea level and room temperature • Turgor pressure is the pressure exerted by the plasma membrane against the cell wall, and the cell wall against the protoplast – Look up what this is right now! – What is it? • Water and minerals can travel through a plant by three routes: – Transmembrane route: out of one cell, across a cell wall, and into another cell – Symplastic route: via the continuum of cytosol – Apoplastic route: via the cell walls and extracellular spaces Mechanisms of Stomatal Opening and Closing • Changes in turgor pressure open and close stomata • These result primarily from the reversible uptake and loss of potassium ions by the guard cells Fig. 36-17 Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed Radially oriented cellulose microfibrils Cell wall Vacuole Guard cell (a) Changes in guard cell shape and stomatal opening and closing (surface view) Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed H2O H2O H2O H2O H2O K+ H2O H2O H2O H2O H2O (b) Role of potassium in stomatal opening and closing Fig. 36-17a Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed Radially oriented cellulose microfibrils Cell wall Vacuole Guard cell (a) Changes in guard cell shape and stomatal opening and closing (surface view) Fig. 36-17b Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed H 2O H2O H 2O H 2O H 2O K+ H 2O H 2O H 2O H 2O (b) Role of potassium in stomatal opening and closing H2O Stimuli for Stomatal Opening and Closing • Generally, stomata open during the day and close at night to minimize water loss • Stomatal opening at dawn is triggered by light, CO2 depletion, and an internal “clock” in guard cells • All eukaryotic organisms have internal clocks; circadian rhythms are 24-hour cycles Bulk Flow by Positive Pressure: The Mechanism of Translocation in Angiosperms • In studying angiosperms, researchers have concluded that sap moves through a sieve tube by bulk flow driven by positive pressure Animation: Translocation of Phloem Sap in Summer Animation: Translocation of Phloem Sap in Spring Fig. 36-20 Vessel (xylem) Sieve tube Source cell (phloem) (leaf) H2O 1 Loading of sugar Sucrose 1 H2O Bulk flow by negative pressure Bulk flow by positive pressure 2 2 Uptake of water 3 Unloading of sugar Sink cell (storage root) 4 Water recycled 3 4 H2O Sucrose Concept 39.2: Plant hormones help coordinate growth, development, and responses to stimuli • Hormones are chemical signals that coordinate different parts of an organism The Discovery of Plant Hormones • Any response resulting in curvature of organs toward or away from a stimulus is called a tropism • Tropisms are often caused by hormones • Phototropism – plant’s response to light Video: Phototropism Fig. 39-5b RESULTS Darwin and Darwin: phototropic response only when tip is illuminated Light Tip removed Tip covered by opaque cap Tip covered by transparent cap Site of curvature covered by opaque shield • The term auxin refers to any chemical that promotes elongation of coleoptiles • Auxin is involved in root formation and branching • Auxin affects secondary growth by inducing cell division in the vascular cambium and influencing differentiation of secondary xylem • Cytokinins are so named because they stimulate cytokinesis (cell division) Control of Cell Division and Differentiation • Cytokinins are produced in actively growing tissues such as roots, embryos, and fruits • Cytokinins work together with auxin to control cell division and differentiation Control of Apical Dominance • Cytokinins, auxin, and other factors interact in the control of apical dominance, a terminal bud’s ability to suppress development of axillary buds • If the terminal bud is removed, plants become bushier Fig. 39-9 Lateral branches “Stump” after removal of apical bud (b) Apical bud removed Axillary buds (a) Apical bud intact (not shown in photo) (c) Auxin added to decapitated stem • Gibberellins have a variety of effects, such as stem elongation, fruit growth, and seed germination Stem Elongation • Gibberellins stimulate growth of leaves and stems • In stems, they stimulate cell elongation and cell division Fruit Growth • In many plants, both auxin and gibberellins must be present for fruit to set • Gibberellins are used in spraying of Thompson seedless grapes Fig. 39-10 (b) Gibberellin-induced fruit growth (a) Gibberellin-induced stem growth Germination • After water is imbibed, release of gibberellins from the embryo signals seeds to germinate Fig. 39-11 1 Gibberellins (GA) 2 Aleurone secretes send signal to aleurone. -amylase and other enzymes. 3 Sugars and other nutrients are consumed. Aleurone Endosperm -amylase GA GA Water Scutellum (cotyledon) Radicle Sugar • Plants produce ethylene in response to stresses such as drought, flooding, mechanical pressure, injury, and infection • The effects of ethylene include response to mechanical stress, senescence, leaf abscission, and fruit ripening • Response to gravity is known as gravitropism • Roots show positive gravitropism; shoots show negative gravitropism • Plants may detect gravity by the settling of statoliths, specialized plastids containing dense starch grains Fig. 39-24 Statoliths (a) Root gravitropic bending 20 µm (b) Statoliths settling • The term thigmomorphogenesis refers to changes in form that result from mechanical disturbance • Rubbing stems of young plants a couple of times daily results in plants that are shorter than controls Fig. 39-26 (a) Unstimulated state (b) Stimulated state Side of pulvinus with flaccid cells Leaflets after stimulation Pulvinus (motor organ) (c) Cross section of a leaflet pair in the stimulated state (LM) Side of pulvinus with turgid cells Vein