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Transcript
Plants, Tissues and Nutrition Plant types and their evolution • Terrestrial plants evolved from aquatic green algae • There are three main types: • Bryophytes- mosses and hornwarts • Ferns, Lycophytes and horsetails • Gymnosperms and angiosperms Fig. 15-1, p.245 charophytes flowering bryophytes lycophytes horsetails ferns cycads ginkgos conifers gnetophytes plants seed plants plants with true leaves vascular plants land plants (closely related groups) Fig. 15-4, p.246 zygote only, no sporophyte green algae bryophytes ferns gymnosperms angiosperms Fig. 15-3, p.246 Bryophytes • Mosses and Hornwarts – “Leaves” have a cuticle to conserve water – A rudimentary root system anchors them to substratum and allows for absorption – Need to live in moist environment – Produce spores and free swimming sperm, need water – Most can survive drying out by going dormant Ferns Lycophytes and Horsetails • Share features with bryophytes • Have rudimentary roots • Have vascular system Carboniferous Lycophytes •Some formed vast forests •Source of our modern “fossil fuels” •Extinct except for a few groups Lepidodendron Fig. 15-7a, p.249 Ferns and Horsetails • Have “true leaves” • Root system • Still need moisture • Produce spores (swimming sperm) vegetative stem strobilus on fertile stem Fig. 15-8c, p.249 Seed Producing plants: Gymnosperms Gymnosperms Have all adaptations for living on land: Produce seeds Have a vascular system Well developed roots “true leaves” conserve water and exchange gases with atmosphere Angiosperms (Flowering Plants) • Flowers – Ovules and (after fertilization) seeds develop in ovary petal stamen (microspores form here) carpel (megaspores form here) sepal ovule in an ovary Fig. 15-14, p.254 Flowering Plants • Have all the same land adaptations as gymnosperms plus flowers • Dominate the plant kingdom • Magnoliids, eudicots and monocots Monocots and Eudicots • Two major plant groups • Same tissues, but arranged in different ways • Eudicots are the more diverse group Monocots and Eudicots • Differ in – Cotyledon number – Leaf venation – Floral parts – Pollen structure – Arrangement of vascular bundles in stem a Eudicots Inside seeds, two cotyledons (seed leaves of embryo) Usually four or five floral parts (or multiples of four or five) Leaf veins usually in a netlike array Three pores and/or furrows in the pollen grain surface Vascular bundles organized as a ring in ground tissue b Monocots Inside seeds, one cotyledon (seed leaf of embryo) Usually three floral parts (or multiples of threes) Leaf veins usually running parallel with one another One pore or furrow in the pollen grain surface Vascular bundles distributed throughout ground tissue Fig. 18-4, p.303 Plant Body Plan • Plant body plan is divided into • Shoots • Roots DERMAL TISSUES VASCULAR TISSUES GROUND TISSUES SHOOT SYSTEM ROOT SYSTEM Body Plan • Ground tissue system- support • Vascular tissue system- transport • Dermal tissue system- conserve water Plant organ and tissue systems • Shoots – Produce food by photosynthesis – Carry out reproductive functions • Roots – Anchor the plant – Penetrate the soil and absorb water and dissolved minerals – Store food shoot tip (terminal bud) activity at meristems primary tissues form as new cells lengthen, differentiate primary tissues form as new cells lengthen, differentiate activity at meristems root tip Fig. 29-3a, p.494 Meristems • Regions where cell divisions produce plant growth • Apical meristems – Lengthen stems and roots – Responsible for primary growth • Lateral meristems – Increase width of stems – Responsible for secondary growth Simple Tissues • Made up of one type of cell – Parenchyma – alive • Found in soft photosynthetic tissues – Collenchyma – alive • Provides support – Sclerenchyma – dead at maturity • Provides even more support Simple Tissues collenchyma celery parenchyma Flax fibers lignified secondary wall Pear fruit Complex Tissues Composed of mixed cell types Xylem Phloem Epidermis Vascular Tissues Xylem Phloem • Conducts water and dissolved minerals • Transports sugars • Conducting cells are dead and hollow at maturity • Main conducting cells are sieve-tube members • Companion cells assist in the loading of sugars one cell’s wall pit in wall a vessel of xylem parenchyma b Tissues in a Stem sieve plate of sieve tube cell companion cell c fibers of sclerenchyma phloem Epidermis • Covers and protects plant surfaces • Secretes a waxy, waterproof cuticle • Contains stomata • In woody plants, periderm replaces epidermis Primary Shoot Structure • Eudicot and monocot stems petiole axillary bud node blade sheath blade stem node Internal Structure of a Eudicot Stem • Outermost layer is epidermis • Cortex lies beneath epidermis • Ring of vascular bundles separates the cortex from the pith • The pith lies in the center of the stem xylem cell epidermis cortex vascular bundle pith companion cell in sieve tube phloem in phloem Fig. 18-5a, p.304 Internal Structure of a Monocot Stem • The vascular bundles are distributed throughout the ground tissue • No division of ground tissue into cortex and pith collenchyma sheath air vessel space in xylem epidermis vascular bundle pith sieve tube in phloem companion cell in phloem Fig. 18-5b, p.304 Adapted to Photosynthesis • Leaves are usually thin – High surface area-to-volume ratio – Promotes diffusion of carbon dioxide in, oxygen out • Leaves are arranged to capture sunlight – Are held perpendicular to rays of sun – Arranged so they don’t shade one another Leaf Structure UPPER EPIDERMIS cuticle PALISADE MESOPHYLL phloem SPONGY MESOPHYLL xylem LOWER EPIDERMIS O2 CO2 one stoma Leaf Veins: Vascular Bundles • Xylem and phloem; often strengthened with fibers • In eudicots, veins are netlike • In monocots, they are parallel p.305 Leaf Epidermis • Covers every leaf surface • Specialized cells Stem Growth and Development • Cells at tip of apical meristem divide • Their descendents divide and differentiate, giving rise to specialized tissues • Lateral buds are undeveloped meristematic tissue that gives rise to stems, leaves, and flowers Stem Development immature leaf shoot apical meristem procambium protoderm procambium ground meristem epidermis cortex primary phloem procambium primary xylem pith Roots Structure • Taproot system – eudicots • Fibrous root system – monocots Root Systems taproot system of a California poppy fibrous root system of a grass plant Root Structure • Root cap covers tip • Apical meristem produces the cap – Cell divisions at the apical meristem cause the root to lengthen – Farther up, cells differentiate and mature • Root Hairs- – Provide large surface area for water and mineral absorption Internal Structure of a Root • Outermost layer is epidermis • Root cortex is beneath the epidermis • Vascular cylinder contains xylem and phloem • Endodermis, then pericycle surround the vascular cylinder • In some plants, there is a central pith VASCULAR CYLINDER endodermis pericycle xylem phloem cortex epidermis root hair Vessel members are mature; root hairs are about to form. New root cells lengthen, sieve tubes mature, vessel members start forming. Most cells have stopped dividing Meristem cells are dividing fast. No cell division is occurring here. root cap root tip Fig. 18-10a, p.307 epidermis root cortex root cortex endodermis pericycle primary xylem primary phloem b Vascular cylinder, cross section Fig. 18-10b, p.307 Secondary Growth • Woody plants • A ring of vascular cambium produces secondary xylem and phloem • Wood is the accumulation of these secondary tissues, especially xylem Secondary Growth Ongoing cell divisions enlarge the inner core of secondary xylem and displace vascular cambium toward the stem. VASCULAR CAMBIUM stem surface primary xylem primary phloem VASCULAR CAMBIUM secondary xylem secondary phloem Fig. 18-11b, p.308 outer surface of stem root division One of the cells vascular cambium at the start of secondary growth. division One of the two daughter cells differentiates into a xylem cell (coded blue), and the other remains meristatic. One of the two daughter cells differentiates into a phloem cell (coded pink), and the other remains meristatic. The same pattern of cell division and differentiation into xylem and phloem cells continues through the growing season. Fig. 18-11c, p.308 Formation of Bark • All tissues outside vascular cambium • Periderm – Cork – New parenchyma – Cork cambium • Secondary phloem Woody Stem periderm BARK vascular cambium secondary phloem HEARTWOOD SAPWOOD Tree Rings • Form as a result of xylem tubes with different diameters – Wide tubes develop during wet season – Narrow tubes develop during dry season – Different diameters create discernable pattern of year’s growth vessel in xylem direction of growth early wood late wood early wood Fig. 18-12b, p.309 Tree Rings cork 2° phloem vascular cambium Annual Growth Ring 2° xylem Late wood Early wood 1° xylem Pith Woods a. Pine b. Oak c. Elm Fig. 18-13b, p.309 Plant Nutrition, Transport and Gas Exchange Soil • Minerals mixed with humus – Minerals come from weathering of rock – Humus is decomposing organic material • Composition of soil varies • Suitability for plant growth depends largely on proportions of soil particles Macronutrients Mineral elements that are required in amounts above 0.5% of the plant’s dry weight Carbon Nitrogen Magnesium Hydrogen Potassium Phosphorus Oxygen Calcium Sulfur Micronutrients Elements that are required in trace amounts for normal plant growth Chlorine Zinc Iron Copper Boron Molybdenum Manganese Leaching • Removal of nutrients from soil by water that percolates through it • Most pronounced in sandy soils • Clays are best at holding onto nutrients Soil Erosion • Loss of soil to wind and water • Often the result of deforestation • Nutrient loss affects entire food chain O HORIZON Fallen leaves and other organic material littering the surface of mineral soil A HORIZON Topsoil, with decomposed organic material; variably deep (only a few centimeters in deserts, elsewhere extending as far as thirty centimeters below the soil surface) B HORIZON Compared with A horizon, larger soil particles, not much organic material, more minerals; extends thirty to sixty centimeters below soil surface C HORIZON No organic material, but partially weathered fragments and grains of rock from which soil forms; extends to underlying bedrock BEDROCK Fig. 18-14a, p.311 Fig. 18-14b, p.311 p.311 Root Hairs • Extensions from the root epidermis • Greatly increase the surface area available for absorption Root Nodules • Swelling on roots of some plants • Contain nitrogen-fixing bacteria • Bacteria convert nitrogen gas to forms plants can use Root Nodules a Root nodule Fig. 18-17a, p.312 Root Nodules Fig. 18-17b, p.312 Mycorrhizae • Symbiosis between young plant root and fungus • Fungal filaments may cover or penetrate root • Fungus absorbs sugars and nitrogen from plant • Roots obtain minerals absorbed from soil by fungus Mycorrhizae Root Structure and Absorption • Roots of most flowering plants have – Endodermis (innermost skin): surrounds vascular cylinder – Exodermis (outer skin): just below surface • Both layers contain a Casparian strip – Controls the flow of water and nutrients Epidermis: (surface skin) in contact with outside environment (leaves and roots) Casparian Strip exodermis root hair epidermis • Prevents water and solutes from passing between cells into vascular cylinder • Water and solutes must flow through cells • Flow is controlled by transport proteins forming vascular cylinder cortex Casparian strip Fig. 18-18, p.313 Plant Nutrient Transport • Simple Diffusion Plant Nutrient Transport • Osmosis Active Transport • Active Transport – uses ATP to move substances across a membrane • ATP - high energy molecule Gas Exchange & Nutrient Exchange • Small Cells – Simple diffusion is adequate Amoeba • Larger Cells – Cytoplasmic Streaming Elodea Water Use and Loss • Plants use a small amount of water for metabolism • Most absorbed water lost to evaporation through stomata in leaves • Evaporation of water from plant parts is transpiration Transpiration • Much water is transpired from leaves • How does water get up to the top of a 300 ft tall tree? Water Transport • Water moves through xylem • Xylem cells are tracheids or vessel members • Both are dead at maturity Tracheids pits in tracheid Tracheids have tapered, unperforated end walls. Pits in adjoining tracheid walls match up. Fig. 18-19a, p.314 vessel member Three adjoining members of a vessel. Thick, finely perforated walls of these dead cells connect to make long vessels, a type of waterconducting tube in xylem. Vessel Members Fig. 18-19b, p.314 perforation plate Vessel Members Perforation plate at the end wall of one type of vessel member. The perforated ends allow water to flow unimpeded. Fig. 18-19c, p.314 Cohesion-Tension Theory of Water Transport • Transpiration creates negative tension in xylem • Tension extends downward from leaves to roots • Hydrogen-bonded water molecules are pulled upward through xylem as continuous columns The Role of Hydrogen Bonds • Hydrogen bonds hold water molecules together in conducting tubes of xylem • Weak bonds still allow water to evaporate through stomata during transpiration Transpiration Drives Water Transport Water evaporates from leaves through stomata Creates a tension in water column in xylem mesophyll (photosynthetic cells) vein upper epidermis a Transpiration is the evaporation of water molecules from aboveground plant parts, especially at stomata. The process puts the water in xylem in a state of tension that extends from roots to leaves. stoma The driving force of evaporation in air Fig. 18-20a2, p.315 Replacement Water Is Drawn in through Roots Fig. 18-20a1, p.315 Wilting • Water regulation maintains turgor Cuticle • Translucent coating secreted by epidermal cells • Consists of waxes in cutin • Allows light to pass through but restricts water loss Plant Cuticle leaf surface cuticle epidermal cell photosynthetic cell Fig. 18-22, p.316 Stomata • Openings across the cuticle and epidermis; allow gases in and out • Guard cells on either side of a stoma • Turgor pressure in guard cells affects opening and closing of stomata Stomata guard cells open stoma chloroplast closed stoma Fig. 18-23, p.316 CAM Plants • Most plants – Stomata open during day and photosynthesis proceeds • CAM plants are better at water conservation – Stomata open at night and carbon dioxide is fixed – Next day, stomata remain closed while carbon dioxide is used Stomata and the Environment Phloem Phloem • Carry organic compounds • Conducting tubes are sieve tubes – Consist of living sieve-tube members • Companion cells – Lie next to sieve tubes – A type of parenchyma – Help load organic compounds into sieve tubes Transport through Phloem • Driven by pressure gradients • Companion cells supply energy to start process sieve tube of the phloem Pressure Flow Theory SOURCE Active transport moves solutes into sieve tubes. Pressure pushes bulk solutes by bulk flow flow between source and sink. Solutes unloaded into sink cells, lowering their water potential; water follows. WATER Water moves in, increasing turgor pressure. Pressure and solute concentrations decrease between source and sink. SINK Phloem one cell of a sieve tube companion cells in the background perforated end plate of sieve tube cell Transportable Organic Compounds • Carbohydrates are stored as starches • Starches, proteins, and fats are too large or insoluble for transport • Cells break them down to smaller molecules for transport – Sucrose is main carbohydrate transported