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Chapters 35-39 All Plants… • multicellular, eukaryotic, autotrophic, alternation of generations Alternation of Generations Sporophyte (diploid) • produces haploid spores via meiosis Gametophyte (haploid) • produce haploid gametes via mitosis Fertilization • joins two gametes to form a zygote Angiosperms Monocots vs. Dicots • named for the number of cotyledons present on the embryo of the plant + monocots - orchids, corn, lilies, grasses + dicots - roses, beans, sunflowers, oaks Plant Morphology Morphology (body form) • shoot and root systems + inhabit two environments - shoot (aerial) + stems, leaves, flowers - root (subterranean) + taproot, lateral roots • vascular tissues + transport materials between roots and shoots - xylem/phloem Plant Anatomy Anatomy (internal structure) • division of labor + cells differing in structure and function - parenchyma, collenchyma, sclerenchyma (below) - water- and food-conducting cells (next slide) Parenchyma St: “typical” plant cells Fu: perform most metabolic functions Collenchyma St: unevenly thickened primary walls Fu: provide support but allow growth in young parts of plants Sclerenchyma St: hardened secondary walls (LIGNIN) Fu: specialized for support; dead Plant cell types Cell wall Parenchyma cells Collenchyma cells Sclerenchyma cells • Xylem • Phloem Plant cell types WATER-CONDUCTING CELLS OF THE XYLEM SUGAR-CONDUCTING CELLS OF THE PHLOEM Sieve-tube members: longitudinal view Vessel Tracheids Pits Companion cell Sieve-tube member Sieve plate Tracheids and vessels Nucleus Vessel element Tracheids Cytoplasm Companion cell Water- and Food-conducting Cells Xylem (water) Phloem (food) • dead at functional maturity • tracheids- tapered with pits • vessel elements- regular tubes • alive at functional maturity • sieve-tube members- arranged end to end with sieve plates & Companion cells Plant Tissues Three Tissue Systems • dermal tissue + epidermis (skin) - single layer of cells that covers entire body - waxy cuticle/root hairs • vascular tissue + xylem and phloem - transport and support • ground tissue + mostly parenchyma - occupies the space b/n dermal/vascular tissue - photosynthesis, storage, support Plant Growth Meristems • perpetually embryonic tissues located at regions of growth + divide to generate additional cells (initials and derivatives) - apical meristems (primary growth- length) + located at tips of roots and shoots - lateral meristems (secondary growth- girth) Roots • A root – Is an organ that anchors the vascular plant – Absorbs minerals and water – Often stores organic nutrients – Taproots found in dicots and gymnosperms – Lateral roots (Branch roots off of the taproot) – Fibrous root system in monocots (e.g. grass) Modified Roots • Many plants have modified roots (a) Prop roots (a) Prop roots (d) Buttress roots (b) Storage roots (b) Storage roots (c) “Strangling” aerial roots (e) Pneumatophores Primary Growth of Roots Primary Growth of Roots • apical meristem + root cap + three overlapping zones - cell division - elongation - maturation Stems • A stem is an organ consisting of – Nodes (could be opposite or alternate) – Internodes Modified Stems (a) Stolons Storage leaves (d) Rhizomes Stem Node Root Bulbs (c) Tubers Rhizome Root Buds • An axillary bud – Is a structure that has the potential to form a lateral shoot, or branch • A terminal bud – Is located near the shoot tip and causes elongation of a young shoot Gardening tip: Removing the terminal bud stimulates growth of axillary buds Primary Growth in Shoots Primary Growth in Shoots • apical meristem (1, 7) + cell division occurs + produces primary meristems - protoderm (4, 8) - procambium (3, 10) - ground meristem (5, 9) • axillary bud meristems + located at base of leaf primordia • leaf primordium (2, 6) + gives rise to leaves The leaf Is the main photosynthetic organ of most vascular plants Leaves generally consist of Blade Stalk Petiole Leaf Morphology • In classifying angiosperms – Taxonomists may use leaf morphology as a criterion (a) Simple leaf Petiole Axillary bud (b) Compound leaf. Leaflet Petiole Axillary bud (c) Doubly compound leaf. Leaflet Petiole Axillary bud Modified Leaves Tendrils Spines Storage leaves Bracts Reproductive leaves. The leaves of some succulents produce adventitious plantlets, which fall off the leaf and take root in the soil. Leaf Anatomy Epidermal Tissue • upper/lower epidermis • guard cells (stomata) Ground Tissue • mesophyll +palisade/spongy parenchyma Vascular Tissue • veins + xylem and phloem Leaf Anatomy Guard cells Key to labels Dermal Ground Stomatal pore Vascular Cuticle Epidermal cell Sclerenchyma fibers 50 µm (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Stoma Upper epidermis Palisade mesophyll Bundlesheath cell Spongy mesophyll Lower epidermis Guard cells Cuticle Vein Xylem Phloem (a) Cutaway drawing of leaf tissues Guard cells Vein Air spaces (c) Transverse section of a lilac (Syringa) leaf (LM) Guard cells 100 µm The Three Tissue Systems: Dermal, Vascular, and Ground Dermal tissue Ground tissue Vascular tissue Dermal Tissue – • • • Protects plant from: Physical damage Pathogens H2O loss (Cuticle) Vascular tissue – Carries out long-distance transport of materials between roots and shoots – Consists of two tissues, xylem and phloem Ground Tissue – Includes various cells specialized for functions such as storage, photosynthesis, and support – Pith = ground tissue internal to the vascular tissue – Cortex = ground tissue external to the vascular tissue Secondary Growth Lateral Meristems • vascular cambium + produces secondary xylem/phloem (vascular tissue) • cork cambium + produces tough, thick covering (replaces epidermis) • secondary growth + occurs in all gymnosperms; most dicot angiosperms The Vascular Cambium and Secondary Vascular Tissue • The vascular cambium – Is a cylinder of meristematic cells one cell thick – Develops from parenchyma cells 2° Growth • As a tree or woody shrub ages – The older layers of secondary xylem, the heartwood, no longer transport water and minerals • The outer layers, known as sapwood – Still transport materials through the xylem Cork Cambium Periderm • protective coat of secondary plant body + cork cambium and dead cork cells - bark • cork cambium produces cork cells CHAPTER 36 • A variety of physical processes – Are involved in the different types of transport 4 Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon for photosynthesis. Some O2 produced by photosynthesis is used in cellular respiration. CO2 O2 5 Sugars are produced by photosynthesis in the leaves. Light H2O Sugar 3 Transpiration, the loss of water from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward. 6 Sugars are transported as phloem sap to roots and other parts of the plant. Water and minerals are transported upward from roots to shoots as xylem sap. 2 1 Roots absorb water and dissolved minerals from the soil. O2 H2O Minerals CO2 7 Roots exchange gases with the air spaces of soil, taking in O2 and discharging CO2. In cellular respiration, O2 supports the breakdown of sugars. The Central Role of Proton Pumps • Proton pumps in plant cells – Create a hydrogen ion gradient – Contribute to membrane potential CYTOPLASM ATP – – – EXTRACELLULAR FLUID + H+ + H+ + H+ H+ H+ H+ – – + + H+ H+ Proton pump generates membrane potential and H+ gradient. • Plant cells use energy stored in the proton gradient and membrane potential – To drive the transport of many different cations CYTOPLASM + – EXTRACELLULAR FLUID – K+ K+ + + – Cations ( K+, for example) are driven into the cell by the membrane potential. K+ K+ K+ K+ K+ – + – + (Membrane potential and cation uptake Transport protein Soil particle – K+ – Cu2+ – – – – – K+ – – K+ Ca2+ Mg2+ H+ H2O + CO2 H2CO3 HCO3– + H+ Root hair (b) Cation exchange in soil. Hydrogen ions (H+) help make nutrients available by displacing positively charged minerals (cations such as Ca2+) that were bound tightly to the surface of negatively charged soil particles. Plants contribute H+ by secreting it from root hairs and also by cellular respiration, which releases CO2 into the soil solution, where it reacts with H2O to form carbonic acid (H2CO3). Dissociation of this acid adds H+ to the soil solution. Figure 37.6b • Cotransport – A transport protein couples the passage of H+ to anions H+ – + – + – + H+ H+ H+ H+ H+ H+ H+ Cotransport of anions – + – + – + H+ H+ H+ H+ Cell accumulates anions ( NO3,–for example) by coupling their transport to the inward diffusion of H+ through a cotransporter. • Cotransport – Is also responsible for the uptake of sucrose by plant cells – H+ H+ + H+ H+ – + – + Plant cells can also accumulate a neutral solute, such as sucrose H+ H+ S –+ H H+ H+ – – + + H+ – Contransport of a neutral solute steep proton gradient. H+ S + ( S ), by cotransporting H+ down the H+ • Water potential – Is a measurement that combines the effects of solute concentration and pressure – Determines the direction of movement of water • Water – Flows from regions of high water potential to regions of low water potential Quantitative Analysis of Water Potential • The addition of solutes – Reduces water potential (a) 0.1 M solution Pure water H2O • Negative pressure – Decreases water potential (d) H2O • Application of physical pressure – Increases water potential (b) (c) H2O H2O Aquaporin Proteins and Water Transport • Aquaporins – Are transport proteins in the cell membrane that allow the passage of water – Do not affect water potential Fluid Movement Movement of fluid in the xylem & phloem is driven by pressure differences at opposite ends of the xylem vessels and sieve tubes • Water and minerals ascend from roots to shoots through the xylem • Plants lose an enormous amount of water through transpiration, the loss of water vapor from leaves and other aerial parts of the plant • The transpired water must be replaced by water transported up from the roots Pushing Xylem Sap: Root Pressure • At night, when transpiration is very low – Root cells continue pumping mineral ions into the xylem of the vascular cylinder, lowering the water potential • Water flows in from the root cortex – Generating root pressure • Root pressure sometimes results in guttation Transpiration produces negative pressure (tension) in the leaf Which exerts a pulling force on water in the xylem, pulling water into the leaf The transpirational pull on xylem sap Is transmitted all the way from the leaves to the root tips and even into the soil solution Is facilitated by cohesion and adhesion • The stomata of xerophytes – Are concentrated on the lower leaf surface – Are often located in depressions that shelter the pores from the dry wind Cuticle Upper epidermal tissue Lower epidermal tissue Trichomes (“hairs”) Stomata 100 m Translocation through Phloem Translocation Is the transport of organic nutrients in the plant Phloem sap Is an aqueous solution that is mostly sucrose Travels from a sugar source to a sugar sink Sugar Source & Sink A sugar source Is a plant organ that is a net producer of sugar, such as mature leaves A sugar sink Is an organ that is a net consumer or storer of sugar, such as a tuber or bulb Transpiration Lab Control of Transpiration Photosynthesis-Transpiration Compromise • guard cells help balance plant’s need to conserve water with its requirement for photosynthesis Stomatal closing • 1. Potassium ions move out of the vacuole and out of the cells. • 2. Water moves out of the vacuoles, following potassium ions. • 3. The guard cells shrink in size. • 4. The stoma closes. Stomatal opening 1. Potassium ions move into the vacuoles. 2. Water moves into the vacuoles, following potassium ions. 3. The guard cells expand. 4. The stoma opens. • Chapter 37 Plant nutrition Plant Nutrition What does a plant need to survive? • 9 macronutrients, 8 micronutrients + macro- required in large quantities - C, H, N, O, P, S, K, Ca, Mg + micro- required in small quantities - Fe, Cl, Cu, Mn, Zn, Mo, B, Ni + usually serve as cofactors of enzymatic reactions • The most common deficiencies – Are those of nitrogen, potassium, and phosphorus Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient • Remove only one macronutrient to see effects on plant Soil Texture and Composition • texture depends on size of particles + sand-silt-clay - loams: equal amounts of sand, silt, clay • composition + horizons - living organic matter - A horizon: topsoil, living organisms, humus - B horizon: less organic, less weathering than A horizon - C Horizon: “parent” material for upper layers • soil conservation issues + fertilizers, irrigation, erosion • A mixture of mineral particles, decaying organic material, living organisms, air, and water, which together support the growth of plants Soil Bacteria and Nitrogen Availability • Nitrogen-fixing bacteria convert atmospheric N2 – plants absorb ammonium (NH4+), nitrate (NO3-) Atmosphere N2 N2 Atmosphere Soil N2 Nitrogen-fixing bacteria Denitrifying bacteria H+ (From soil) Soil NH4 NH3 (ammonia) + – + NH4 (ammonium) Organic material (humus) Nitrate and nitrogenous organic compounds exported in xylem to shoot system Nitrifying bacteria NO3 (nitrate) Ammonifying bacteria Root Nutritional Adaptations Symbiotic Relationships • symbiotic nitrogen fixation + Legume root nodules contain bacteroids (Rhizobium bacteria) - mutualistic relationship - Crop rotation (Legumes • mycorrhizae + symbiotic associations of fungi and roots - mutualistic relationship • parasitic plants + plants that supplement their nutrition from host - mistletoe, dodder plant, Indian pipe • carnivorous plants + supplement nutrition by digesting animals Mycorrhizae and Plant Nutrition • Mycorrhizae – Are modified roots consisting of mutualistic associations of fungi and roots • The fungus – Benefits from a steady supply of sugar donated by the host plant • In return, the fungus – Increases the surface area of water uptake and mineral absorption and supplies water and minerals to the host plant • Unusual nutritional adaptations in plants EPIPHYTES Staghorn fern, an epiphyte PARASITIC PLANTS Host’s phloem Dodder Haustoria Mistletoe, a photosynthetic parasite Dodder, a nonphotosynthetic parasite Indian pipe, a nonphotosynthetic parasite CARNIVOROUS PLANTS Venus’ flytrap Pitcher plants Sundews Phytoremediation • Poplars remove nitrates • Mustard removes uranium Pesticide Levels (ppb) in Ground Water Before & After Phytoremediation Activities Wetlands Uptake of Soil Solution Symplastic Route • continuum of cytosol based on plasmodesmata Apoplastic Route • continuum of cell walls and extracellular spaces Lateral transport of soil solution alternates between apoplastic and symplastic routes until it reaches the Casparian strip Casparian Strip A belt of suberin (purple) that blocks the passage of water and dissolved minerals. Chapter 38 PLANT REPRODUCTION Plant Reproduction Sporophyte (diploid) • produces haploid spores via meiosis Gametophyte (haploid) • produce haploid gametes via mitosis Fertilization • joins two gametes to form a zygote • An overview of angiosperm reproduction Stigma Anther Stamen Carpel Germinated pollen grain (n) (male gametophyte) on stigma of carpel Anther at tip of stamen Style Filament Ovary (base of carpel) Ovary Pollen tube Ovule Embryo sac (n) (female gametophyte) Sepal Egg (n) FERTILIZATION Petal Receptacle Sperm (n) Mature sporophyte Seed plant (2n) with (develops flowers from ovule) (a) An idealized flower. Key Zygote (2n) Seed Haploid (n) Diploid (2n) (b) Simplified angiosperm life cycle. See Figure 30.10 for a more detailed version of the life cycle, including meiosis. Germinating seed Embryo (2n) (sporophyte) Simple fruit (develops from ovary) Mechanisms That Prevent SelfFertilization Stigma Stigma Pin flower Thrum flower Anther with pollen The most common anti-selfing mechanism in flowering plants Is known as self-incompatibility, the ability of a plant to reject its own pollen Preventative Selfing • Some plants – Reject pollen that has an S-gene matching an allele in the stigma cells • Recognition of self pollen – Triggers a signal transduction pathway leading to a block in growth of a pollen tube Double Fertilization Double Fertilization • pollen grain lands on stigma + pollen tube toward ovule + both sperm discharged down the tube - egg and one of the sperm produce zygote - 2 polar nuclei and sperm cell produce endosperm + ovule becomes the seed coat + ovary becomes the fruit Seed Structure and Development • The radicle – Is the first organ to emerge from the germinating seed • In many eudicots – A hook forms in the hypocotyl, and growth pushes the hook above ground Foliage leaves Cotyledon Epicotyl Hypocotyl Cotyledon Cotyledon Hypocotyl Hypocotyl Radicle Seed coat • Monocots – Use a different method for breaking ground when they germinate • The coleoptile – Pushes upward through the soil and into the air Foliage leaves Coleoptile Coleoptile Radicle Chapter 39 PLANT RESPONSES TO INTERNAL AND EXTERNAL SIGNALS Tropisms • Growth toward or away from a stimulus • Gravitropism (Gravity) • Phototropism (Light) • Thigmotropism (Touch) Etiolation • The stems of plants raised in the dark elongate much more rapidly than normal, a phenomenon called etiolation. Signal Transduction Pathway CELL WALL 1 Reception CYTOPLASM 2 Transduction Relay molecules Receptor Hormone or environmental stimulus Plasma membrane Figure 39.3 3 Response Activation of cellular responses Plant hormones help coordinate growth, development, and responses to stimuli • Hormones – Are chemical signals that coordinate the different parts of an organism Photoperiod, the relative lengths of night and day + Is the environmental stimulus plants use most often to detect the time of year