Im chapter27


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Im chapter27

  1. 1. 27______________________________________________________________________________________________PLANT FORM AND FUNCTIONChapter OutlineIMPACTS/ISSUES: LEAFY CLEAN-UP SECONDARY GROWTH CREWS PLANT NUTRITIONORGANIZATION OF THE PLANT BODY Plant Nutrients and Properties of Soil Tree Plant Tissue Systems Root Adaptations of Nutrient Uptake Simple Tissues WATER AND SOLUTE MOVEMENT IN Vascular Tissues PLANTS Dermal Tissues Controlling Water Loss Eudicots and Monocots Distribution of SugarsPRIMARY SHOOTS AND ROOTS IMPACTS/ISSUES REVISITED Inside a Stem SUMMARY Leaf Structure SELF-QUIZ Primary Growth of a Shoot CRITICAL THINKING Structure and Development of Primary RootsObjectives • Define phytoremediation. • Explain why phytoremediation is appealing as a way to clean up toxic chemicals. • State the threats posed to animals by TCE. • List the three major groups of the plant kingdom. • Briefly state the function of stems and roots. • Compare and contrast the ground tissue system, vascular tissue system, and dermal tissue system. • Describe parenchyma, collenchyma, and sclerenchyma tissue. • Explain the functions of xylem and phloem. • Describe the structure and function of epidermal cells. • Compare and contrast eudicots and monocots. • Describe the vascular bundle of eudicots and monocots. • Know the parts of a typical leaf. Plant Form and Function 239
  2. 2. • Define apical meristem. • Explain the function of stomata and guard cells. • Describe the parts of a root, including root hairs and vascular cylinder. • Explain how wood and bark are formed. • Define lateral meristem. • Explain the difference between heartwood and sapwood. • Name the 16 required elements for plant growth, specifying the nine macronutrients. • Discuss why plants grow best in humus. • Explain how a mycorrhiza functions. • Describe nitrogen fixation. • Explain the cohesion-tension theory. • Define transpiration. • Explain the pressure flow theory. • Define translocation.Key Termsdermal tissue system apical meristem vascular cylinderground tissue system guard cell woodparenchyma meristem humusvascular tissue system primary growth cohesion-tension theorycollenchyma bark mycorrhizacompanion cell cork nitrogen fixationcotyledon cork cambium root nodulesepidermis lateral meristem pressure flow theoryphloem periderm translocationsclerenchyma root hairs transpirationvascular bundle secondary growthxylem vascular cambiumLecture Outline27.1 Impacts/Issues: Leafy Clean-Up Crews A. Phytoremediation is the use of plants to remove toxic chemicals from soil water. 1. Poplar trees are used to phytoremediate a site in Maryland that contains chemicals such as TCE, lead, arsenic, mercury, and other metals. a. Without this remediation, the substances would leak into Chesapeake Bay and nearby marshes. 2. Phytoremediation is less expensive than other methods and more visually appealing. a. Some toxins are broken down by plants, but some are released into the atmosphere which is preferable to having them in groundwater.27.2 Organization of the Plant Body A. There are 260,000 species of flowering plants, which dominate the plant kingdom. 1. Major groups of plants are magnoliids, eudicots, and monocots.240 Chapter Twenty-Seven
  3. 3. 2. Above-ground shoots consists of plant stems and leaves.3. Roots are below ground and absorb water and dissolved minerals and store food. a. Roots may also anchor the plant. Plant Form and Function 241
  4. 4. B. Three plant tissue systems 1. Ground tissue system a. makes up the bulk of the plant b. carries out photosynthesis and food storage 2. Vascular tissue system a. pipelines that thread throughout the plant b. distribute water and nutrients to all parts of the plant 3. Dermal tissue system a. covers and protects the plant’s exposed surfaces C. Simple tissues 1. Parenchyma a. makes up most of the soft growth of roots, stems, leaves, flowers b. cells are thin-walled, alive, flexible and many-sided c. can divide to repair wounds in plants 2. Collenchyma a. elongated, stretchable cells that support rapidly growing plant parts 3. Sclerenchyma a. variable shape, dead at maturity b. contains lignin that protects and structurally supports upright plants c. long fibers that can twist but resist stretching d. fibers are useful as materials for cloth, rope, paper, and other products D. Vascular tissues 1. Xylem a. It conducts water and minerals through the plant. b. It is dead at maturity. c. Walls contain lignin and are waterproof. d. Water moves up xylem tubes but also laterally through perforations in adjoining cell walls. 2. Phloem a. Phloem conducts sugars and other organic substances from photosynthetic cells to other parts of the plant. E. Dermal tissues 1. Epidermis is a single layer of cells on a plant. a. Epidermal cells secrete cutin, a waxy polymer of fatty acids. b. Specialized cells within the epidermis are stomata, which control the diffusion of water vapor, oxygen, and carbon dioxide in and out of the plant. F. Eudicots and monocots 1. The two major plant groups are categorized according to the shape of their seed leaves or cotyledons. a. Monocot characteristics: one cotyledon flower parts in threes leaf veins are parallel pollen grains have one pore or furrow vascular bundles are throughout ground tissue b. Eudicot characteristics:242 Chapter Twenty-Seven
  5. 5. two cotyledons flower parts in fours or fives leaf veins are net-like pollen grains have three pores or furrows vascular bundles are in a ring arrangement 2. Most typical plants such as roses, maple trees, and shrubs are eudicots. 3. Lilies, orchids, tulips and grasses are monocots.27.3 Primary Shoots and Roots A. Inside a stem 1. The three tissue groups are organized in predictable patterns. a. Vascular bundles contain xylem and phloem. b. Eudicot vascular bundles form a ring that parallels the long axis of the plant. c. Monocot vascular bundles are distributed throughout the ground tissue. B. Leaf structure 1. Leaf shapes and orientation are adaptations that promote light gathering and gas exchange for photosynthesis. a. Most leaves have flat blades. b. Many stay perpendicular to the sun during the day. c. Leaves of plants in arid regions stay parallel to the sun to conserve water. d. Most leaves are thin with high surface to volume ratios. e. Some leaves are thick or needlelike to conserve water. 2. Epidermis covers the surface and may be smooth, sticky, waxy, hairy or spiky, and contain scales or hooks. a. The waxy cuticle slows water loss from the sheet-like epidermal cells. 3. The bulk of leaf tissue is parenchymous mesophyll that is photosynthetic. 4. Parenchyma is arranged in two layers of mesophyll. a. Palisade parenchyma is the upper layer and contains a higher density of chloroplasts. b. Spongy parenchyma is the lower layer and has spaces between the cells. 5. Leaf veins are arranged in vascular bundles strengthened with fibers. a. Xylem and phloem conduct water, nutrients, and products of photosynthesis within the plant. 6. Stomata and their surrounding guard cells exist primarily on the under side of the leaf. a. When stomata open or close, due to shape changes, carbon dioxide moves into the parenchyma, and oxygen moves out. C. Primary growth of a shoot 1. Growth in plants occurs only in localized areas called meristems. a. Primary growth is the lengthening of root or shoot. b. Lengthening occurs at apical meristems—areas at the tips of roots and shoots. c. Meristem cells are the precursors of dermal, vascular, and ground tissues. d. Buds occur in areas where apical meristem tissue exists that can become new leaves. e. A region of stem where one or more leaves can develop is called a node. 2. Division of cells in an axillary bud can give rise to a branch, leaf, or flower. D. Structure and growth of primary roots Plant Form and Function 243
  6. 6. 1. The root system grows through the soil and takes up water and mineral nutrients. 2. Some eudicots have taproot systems: one large primary root and lateral branching. 3. Most monocots have fibrous root systems with adventitious roots forming from the stem that are similar in diameter and length. 4. Roots have differentiated tissue in the three categories found in shoots: vascular, ground, and dermal. 5. Roots have active apical meristems, similar to shoots. a. Root epidermis is the absorptive interface with soil. b. Fine extensions called root hairs increase the surface area for taking up water and nutrients. 6. Root vascular cylinders are central columns of conductive tissue. a. Eudicots primarily contain xylem and phloem. b. Monocot roots are divided into pith and cortex. c. Pericycle is an array of parenchyma cells that sheaths the cylinder.27.4 Secondary Growth A. Secondary growth is the woody, thickening that occurs over time. 1. Cell divisions in lateral meristem tissue give rise to secondary growth. 2. Lateral meristems run lengthwise through roots and stems and exist in two forms: a. vascular cambium b. cork cambium 3. Vascular cambium produces secondary xylem inside the cylinder and secondary phloem outside the cylinder. 4. A core of secondary xylem or wood may comprise up to 90% of a plant’s weight. 5. Periderm is a dermal tissue comprised of parenchyma and cork. 6. Bark is secondary phloem and periderm. 7. Cork is waxy, densely packed dead cells. a. Cork protects, insulates, and waterproofs stem or root surface. b. Cork forms over wounded tissue. 8. As stems and roots age, metabolic wastes fill the oldest xylem and clog it so it no longer functions to transport substances. a. This darkened area is called heartwood. 9. Sapwood is moist, fully functioning xylem between the heartwood and vascular cambium. 10. Vascular cambium is inactive during cold winters or long dry spells. 11. Bands of early and late wood, alternating in sections, create growth rings or tree rings. a. In regions where growth is suspended for part of the year, growth rings are visible. b. In regions where growth is continual during the year, growth rings do not exist.27.5 Plant Nutrition A. Plant nutrients and properties of soil 1. Plant growth requires 16 elements. a. Nine macronutrients are: carbon, hydrogen, oxygen, nitrogen, potassium, calcium, magnesium, phosphorus, and sulfur. b. Seven micronutrients are: chlorine, iron, boron, manganese, zinc, copper, and molybdenum. 2. Soil with decaying organic matter (humus) is best for plant growth.244 Chapter Twenty-Seven
  7. 7. 3. Silt, sand, and clay are possible mineral particles in soil. a. Sand is the largest particle; silt is intermediate, and clay is smaller. b. Different sized particles contribute different properties to soil. c. A soil with a combination of all three can sustain movement of dissolved nutrients and yet holds water and allows for movement of air between particles. Plant Form and Function 245
  8. 8. B. Root adaptations for nutrient uptake 1. Root specializations help plants take up water and nutrients. a. Root hairs vastly increase surface area for absorption. b. Root hairs are fragile; each one only lasts a few days. 2. Mycorrhizae are the result of symbiotic action between fungus and roots. a. Mycorrhizae produce filaments called hyphae. b. Hyphae vastly increase surface area for absorption. c. The root benefits by absorbing scarce minerals it would not be able to absorb on its own. d. The fungus obtains sugars from the root. 3. Nitrogen fixation is accomplished by extracting the abundant nitrogen gas from the atmosphere into the plant. a. Plants require nitrogen fixing bacteria in order to carry out nitrogen fixation. b. Nitrogen fixing bacteria reside in root nodules. c. Legumes typically have nitrogen fixing bacteria.27.6 Water and Solute Movement in Plants A. Water entering a root moves into the xylem of the root vascular bundle. 1. Water moves up a plant from the root to the top. a. Sometimes this can mean moving uphill more than 100 meters. b. No pumping action is possible inside a plant vascular bundle. 2. The cohesion-tension theory explains that water moves uphill as it is pulled from the top by negative pressure called tension (as water evaporates from the top of the plant). 3. Transpiration is the evaporation of water from the above-ground parts of a plant. a. This process results in water being pulled up from the bottom of the plant. b. A continuous column of water will exert force that moves water toward the lowest pressure. 4. Photosynthesis and other processes within the plant can contribute to the negative pressure that pulls a water column up through a plant. B. Controlling water loss 1. The waxy cuticle, secreted by the epidermal cells, is waterproof and helps prevent water loss from plants. 2. Most of the water in plants evaporates through the stomata (about 98%). a. Stomata react to turgidity in the plant and close if the plant wilts (to prevent further water loss). 3. The stomata also react to environmental cues such as carbon dioxide levels and light intensity. a. Osmotic pressure changes in guard cells around the stomata and open or close the stomata. b. When the sun comes up, guard cells pump potassium into their cytoplasm. c. This in turn increases osmotic pressure, and guard cells plump up. d. Stomata open to let carbon dioxide enter the plant, and photosynthesis begins. C. Distribution of sugars 1. Phloem cells, (sieve tubes), are living cells that distribute sugars. a. Sieve tube cells are porous. b. Organic compounds flow through the tubes.246 Chapter Twenty-Seven
  9. 9. 2. Companion cells around the sieve tubes actively transport photosynthetic products into the tubes. 3. Translocation is the term for movement of organic substances through phloem. 4. Source areas are where organic compounds are loaded into sieve tubes. 5. Sink areas are where organic compounds are being used or stored. 6. Organic molecules flow from a source to a sink through phloem. D. Pressure flow theory states that pressure builds up at the source end and drives the solute-rich fluid toward the sink. E. Energy requiring reactions load sugars into sieve tubes. 1. Sugars increase the solute concentration in the tubes, which causes osmosis and water loading. 2. Water increases the fluid volume and internal pressure in the tubes. 3. High pressure pushes the fluid toward the sink regions in the plant. 4. Sugars are unloaded at the sink region, and water flows out of the tubes by osmosis.27.7 Impacts/Issues Revisited: Leafy Clean-Up Crews A. The best phytoremediation occurs when the plant can actually break down the toxin into a less toxic molecule. 1. Gene transfers can provide this ability to some plants. 2. Research is focused on transferring genes from bacteria, so plants are more efficient at this process. B. A less desirable form of phytoremediation involves safe disposal of toxic laden plants that cannot break down the toxins (although they were able to remove them from ground water). 2. wer is a monocot because it has six petals, or two groups of three. Plant Form and Function 247