Chapter 23 Lecture- Roots, Stems, Leaves


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Chapter 23 Lecture for Lab Biology

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  • Chapter 23 Lecture- Roots, Stems, Leaves

    1. 2. 23–1 Specialized Tissues in Plants
    2. 3. <ul><ul><li>The three principal organs of seed plants are roots, stems, and leaves. </li></ul></ul><ul><ul><li>These organs perform functions such as the transport of nutrients, protection, and coordination of plant activities. </li></ul></ul>Seed Plant Structure
    3. 4. <ul><li>Roots: </li></ul><ul><ul><ul><li>absorb water and dissolved nutrients. </li></ul></ul></ul><ul><ul><ul><li>anchor plants in the ground. </li></ul></ul></ul><ul><ul><ul><li>protect the plant from harmful soil bacteria and fungi. </li></ul></ul></ul>Seed Plant Structure
    4. 5. <ul><li>Stems provide: </li></ul><ul><ul><ul><li>a support system for the plant body. </li></ul></ul></ul><ul><ul><ul><li>a transport system that carries nutrients. </li></ul></ul></ul><ul><ul><ul><li>a defense system that protects the plant against predators and disease. </li></ul></ul></ul>Seed Plant Structure
    5. 6. <ul><li>Leaves: </li></ul><ul><ul><ul><li>are a plant’s main photosynthetic systems. </li></ul></ul></ul><ul><ul><ul><li>increase the amount of sunlight plants absorb. </li></ul></ul></ul><ul><li>Adjustable pores conserve water and let oxygen and carbon dioxide enter and exit the leaf. </li></ul>Seed Plant Structure
    6. 7. <ul><ul><li>Plants consist of three main tissue systems: </li></ul></ul><ul><ul><ul><li>dermal tissue </li></ul></ul></ul><ul><ul><ul><li>vascular tissue </li></ul></ul></ul><ul><ul><ul><li>ground tissue </li></ul></ul></ul>Plant Tissue Systems
    7. 8. Seed Plant Structure Leaf Stem Root
    8. 9. Dermal Tissue <ul><ul><ul><li>Dermal tissue is the outer covering of a plant and consists of epidermal cells. </li></ul></ul></ul><ul><ul><ul><li>Epidermal cells make up dermal tissue. </li></ul></ul></ul><ul><ul><ul><li>Epidermal cells are covered with a thick waxy layer, called the cuticle , which protects the plant against water loss and injury. </li></ul></ul></ul>
    9. 10. Dermal Tissue <ul><li>Some epidermal cells have projections called trichomes, that help protect the leaf and also give it a fuzzy appearance. </li></ul><ul><li>In roots, dermal tissue includes root hair cells that provide a large amount of surface area and aid in water absorption. </li></ul><ul><li>On the underside of leaves, dermal tissue contains guard cells, which regulate water loss and gas exchange. </li></ul>
    10. 11. Vascular Tissue <ul><li>Vascular tissue forms a transport system that moves water and nutrients throughout the plant. </li></ul><ul><li>Vascular tissue is made up of xylem, a water-conducting tissue, and phloem, a food-conducting tissue. </li></ul>
    11. 12. Vascular Tissue <ul><ul><li>Vascular tissue contains several types of specialized cells. </li></ul></ul><ul><ul><ul><li>Xylem consists of tracheids and vessel elements. </li></ul></ul></ul><ul><ul><ul><li>Phloem consists of sieve tube elements and companion cells. </li></ul></ul></ul>
    12. 13. Vascular Tissue Xylem Phloem Tracheid Vessel element Companion cell Sieve tube element Cross Section of a Stem
    13. 14. Vascular Tissue <ul><ul><li>Xylem </li></ul></ul><ul><ul><ul><li>All seed plants have tracheids. </li></ul></ul></ul><ul><ul><ul><li>Tracheids are long, narrow cells that are impermeable to water, but they have holes that connect cells. </li></ul></ul></ul>Tracheid Vessel element
    14. 15. Vascular Tissue <ul><li>Angiosperms also have vessel elements. </li></ul><ul><li>Vessel elements form a continuous tube through which water can move. </li></ul>Tracheid Vessel element
    15. 16. Vascular Tissue <ul><ul><li>Phloem </li></ul></ul><ul><ul><ul><li>Phloem contains sieve tube elements and companion cells. </li></ul></ul></ul><ul><ul><ul><li>Sieve tube elements are phloem cells joined end-to-end to form sieve tubes. </li></ul></ul></ul>Sieve tube element Companion cell
    16. 17. Vascular Tissue <ul><ul><ul><li>The end walls of sieve tube elements have many small holes that sugars and other foods can move through. </li></ul></ul></ul>Companion cell Sieve tube element
    17. 18. Vascular Tissue <ul><li>Companion cells are phloem cells that surround sieve tube elements. </li></ul><ul><li>Companion cells support sieve tubes and aid in the movement of substances in and out of the phloem. </li></ul>Sieve tube element Companion cell
    18. 19. <ul><ul><ul><li>Between dermal and vascular tissues are ground tissues. </li></ul></ul></ul><ul><ul><ul><li>Three kinds of ground tissue: </li></ul></ul></ul><ul><ul><ul><ul><li>Parenchyma- thin walls and large central vacuoles </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Collenchyma- strong, flexible cell walls that help support larger plants </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Sclerenchyma- extremely thick, rigid cell walls = tough and strong </li></ul></ul></ul></ul>
    19. 20. Plant Growth and Meristematic Tissue <ul><ul><ul><li>In most plants, new cells are produced at the tips of the roots and stems. </li></ul></ul></ul><ul><ul><ul><li>These cells are produced in meristems. </li></ul></ul></ul><ul><ul><ul><li>A meristem is a cluster of tissue that is responsible for continuing growth throughout a plant's lifetime. </li></ul></ul></ul>
    20. 21. <ul><li>The new cells produced in meristematic tissue are undifferentiated. </li></ul><ul><li>As the cells develop into mature cells, they differentiate to produce dermal, ground, and vascular tissue. </li></ul>Plant Growth and Meristematic Tissue
    21. 22. <ul><li>Near the tip of each growing stem and root is an apical meristem. </li></ul><ul><li>An apical meristem is at the tip of a growing stem or root. </li></ul>Plant Growth and Meristematic Tissue
    22. 23. <ul><ul><li>Meristematic tissue is the only plant tissue that produces new cells by mitosis. </li></ul></ul>Plant Growth and Meristematic Tissue
    23. 24. 23–2 Roots
    24. 25. <ul><li>In some plants, the primary root grows long and thick and is called a taproot . </li></ul><ul><li>Fibrous roots branch to such an extent that no single root grows larger than the rest. </li></ul>Types of Roots
    25. 26. <ul><li>A carrot is an example of a taproot. </li></ul>Types of Roots Taproot Fibrous Roots
    26. 27. <ul><li>Fibrous roots are found in grasses. </li></ul>Types of Roots Fibrous Roots
    27. 28. Root Structure and Growth <ul><ul><ul><li>Roots contain cells from dermal, vascular, and ground tissue. </li></ul></ul></ul>
    28. 29. <ul><ul><li>A mature root has an outside layer, the epidermis, and a central cylinder of vascular tissue. </li></ul></ul><ul><ul><li>Between these two tissues lies a large area of ground tissue. </li></ul></ul><ul><ul><li>The root system plays a key role in water and mineral transport. </li></ul></ul>Root Structure and Growth
    29. 30. <ul><li>The root’s surface is covered with cellular projections called root hairs. Root hairs provide a large surface area through which water can enter the plant. </li></ul>Root Structure and Growth Root hairs
    30. 31. <ul><li>The epidermis (including root hairs) protects the root and absorbs water. </li></ul>Root Structure and Growth Epidermis
    31. 32. <ul><li>Inside the epidermis is a layer of ground tissue called the cortex. </li></ul>Root Structure and Growth Ground tissue (cortex)
    32. 33. <ul><li>The cortex extends to another layer of cells, the endodermis. </li></ul><ul><li>The endodermis completely encloses the vascular cylinder. </li></ul>Root Structure and Growth Endodermis
    33. 34. <ul><li>The vascular cylinder is the central region of a root that includes the xylem and phloem. </li></ul>Root Structure and Growth Vascular cylinder Phloem Xylem
    34. 35. <ul><li>Roots grow in length as their apical meristem produces new cells near the root tip. </li></ul>Root Structure and Growth Apical meristem
    35. 36. <ul><li>These new cells are covered by the root cap that protects the root as it forces its way through the soil. </li></ul>Root Structure and Growth Root cap Apical meristem
    36. 37. Root Functions <ul><ul><li>Roots anchor a plant in the ground and absorb water and dissolved nutrients from the soil. </li></ul></ul>
    37. 38. Root Functions <ul><ul><li>Uptake of Plant Nutrients </li></ul></ul><ul><ul><ul><li>To grow, flower, and produce seeds, plants need a variety of inorganic nutrients in addition to carbon dioxide and water. </li></ul></ul></ul>
    38. 39. Root Functions <ul><li>The most important nutrients plants need include: </li></ul><ul><ul><ul><li>nitrogen </li></ul></ul></ul><ul><ul><ul><li>phosphorus </li></ul></ul></ul><ul><ul><ul><li>potassium </li></ul></ul></ul><ul><ul><ul><li>magnesium </li></ul></ul></ul><ul><ul><ul><li>calcium </li></ul></ul></ul>
    39. 40. Root Functions <ul><ul><li>Active Transport of Minerals </li></ul></ul><ul><ul><ul><li>The cell membranes of root epidermal cells contain active transport proteins. </li></ul></ul></ul>
    40. 41. Root Functions <ul><ul><ul><li>Transport proteins use ATP to pump mineral ions from the soil into the plant. </li></ul></ul></ul>Root hairs
    41. 42. Root Functions <ul><li>The high concentration of mineral ions in the plant cells causes water molecules to move into the plant by osmosis. </li></ul>
    42. 43. Root Functions <ul><ul><li>Movement Into the Vascular Cylinder </li></ul></ul><ul><ul><ul><li>Osmosis and active transport move water and minerals from the root epidermis into the cortex. </li></ul></ul></ul><ul><ul><ul><li>The water and dissolved minerals pass the inner boundary of the cortex and enter the endodermis. </li></ul></ul></ul>
    43. 44. Root Functions <ul><li>The endodermis is composed of many individual cells. </li></ul>Endodermis
    44. 45. Root Functions <ul><li>Each cell is surrounded on four sides by a waterproof strip called a Casparian strip. </li></ul>Casparian strip Casparian strip
    45. 46. Root Functions <ul><li>The Casparian strip prevents the backflow of water out of the vascular cylinder into the root cortex. </li></ul>
    46. 47. Root Functions <ul><ul><ul><li>Water moves into the vascular cylinder by osmosis. </li></ul></ul></ul><ul><ul><ul><li>Because water and minerals cannot pass through the Casparian strip, once they pass through the endodermis, they are trapped in the vascular cylinder. </li></ul></ul></ul><ul><ul><ul><li>As a result, there is a one-way passage of materials into the vascular cylinder in plant roots. </li></ul></ul></ul>
    47. 48. Root Functions <ul><ul><li>Root Pressure </li></ul></ul><ul><ul><ul><li>As minerals are pumped into the vascular cylinder, more and more water follows by osmosis, producing a strong pressure. </li></ul></ul></ul><ul><ul><ul><li>This root pressure forces water through the vascular cylinder and into the xylem. </li></ul></ul></ul>
    48. 49. Root Functions <ul><li>As more water moves from the cortex into the vascular cylinder, more water in the xylem is forced upward through the root into the stem. </li></ul><ul><li>Root pressure pushes water through the vascular system of the entire plant. </li></ul>
    49. 50. 23–3 Stems
    50. 51. <ul><ul><li>Stem functions: </li></ul></ul><ul><ul><ul><li>they produce leaves, branches and flowers </li></ul></ul></ul><ul><ul><ul><li>they hold leaves up to the sunlight </li></ul></ul></ul><ul><ul><ul><li>they transport substances between roots and leaves </li></ul></ul></ul><ul><ul><ul><li>Can do photosynthesis </li></ul></ul></ul>Stem Structure and Function
    51. 52. <ul><li>Stems make up an essential part of the water and mineral transport systems of the plant. </li></ul><ul><li>Xylem and phloem form continuous tubes from the roots through the stems to the leaves. </li></ul><ul><li>This allows water and nutrients to be carried throughout the plant. </li></ul>Stem Structure and Function
    52. 53. <ul><li>Stems are surrounded by a layer of epidermal cells that have thick cell walls and a waxy protective coating. </li></ul>Stem Structure and Function
    53. 54. <ul><ul><ul><li>Leaves attach to the stem at structures called nodes. </li></ul></ul></ul><ul><ul><ul><li>The regions of stem between the nodes are internodes. </li></ul></ul></ul><ul><ul><ul><li>Small buds are found where leaves attach to nodes. </li></ul></ul></ul>Stem Structure and Function Node Internode Bud Node
    54. 55. <ul><li>Buds contain undeveloped tissue that can produce new stems and leaves. </li></ul><ul><li>In larger plants, stems develop woody tissue that helps support leaves and flowers. </li></ul>Stem Structure and Function Bud
    55. 56. Monocot and Dicot Stems <ul><ul><li>In monocots, vascular bundles are scattered throughout the stem. </li></ul></ul><ul><ul><li>In dicots and most gymnosperms, vascular bundles are arranged in a ringlike pattern. </li></ul></ul>
    56. 57. <ul><ul><li>Monocot Stems </li></ul></ul><ul><ul><ul><li>Monocot stems have a distinct epidermis, which encloses vascular bundles. </li></ul></ul></ul><ul><ul><ul><li>Each vascular bundle contains xylem and phloem tissue. </li></ul></ul></ul>Monocot and Dicot Stems
    57. 58. <ul><ul><ul><li>Vascular bundles are scattered throughout the ground tissue. </li></ul></ul></ul><ul><ul><ul><li>Ground tissue consists mainly of parenchyma cells. </li></ul></ul></ul>Monocot and Dicot Stems Monocot Vascular bundles Epidermis Ground tissue
    58. 59. <ul><ul><li>Dicot Stems </li></ul></ul><ul><ul><ul><li>Dicot stems have vascular bundles arranged in a ringlike pattern. </li></ul></ul></ul><ul><ul><ul><li>The parenchyma cells inside the vascular tissue are known as pith. </li></ul></ul></ul>Monocot and Dicot Stems Dicot Cortex Pith Vascular bundles Epidermis
    59. 60. <ul><ul><ul><li>The parenchyma cells outside of the vascular tissue form the cortex of the stem. </li></ul></ul></ul>Dicot Cortex Pith Vascular bundles Epidermis
    60. 61. Primary Growth of Stems <ul><ul><ul><li>All seed plants undergo primary growth , which is an increase in length. </li></ul></ul></ul><ul><ul><ul><li>For the entire life of the plant, new cells are produced at the tips of roots and shoots. </li></ul></ul></ul>Year 1 Year 2 Year 3 Primary growth Apical meristem Primary growth Leaf scar
    61. 62. <ul><ul><li>Primary growth of stems is produced by cell divisions in the apical meristem. It takes place in all seed plants. </li></ul></ul>Primary Growth of Stems Apical meristem
    62. 63. Secondary Growth of Stems <ul><ul><li>Stems increase in width due to secondary growth . </li></ul></ul><ul><ul><li>Secondary growth produces wood. </li></ul></ul><ul><ul><li>Thin tree ring = slow growth, often due to drought. </li></ul></ul>
    63. 64. <ul><li>Vascular cambium produces vascular tissues and increases the thickness of stems over time. </li></ul><ul><li>Cork cambium produces the outer covering of stems. </li></ul><ul><li>The addition of new tissue in these cambium layers increases the thickness of the stem. </li></ul>Secondary Growth of Stems
    64. 65. <ul><ul><li>Formation of the Vascular Cambium </li></ul></ul><ul><ul><ul><li>Once secondary growth begins, the vascular cambium appears as a thin layer between the xylem and phloem of each vascular bundle. </li></ul></ul></ul>Secondary Growth of Stems Vascular cambium
    65. 66. <ul><li>The vascular cambium divides to produce xylem cells toward the center of the stem and phloem cells toward the outside. </li></ul>Secondary Growth of Stems Secondary xylem Secondary phloem
    66. 67. Secondary Growth of Stems <ul><li>These different tissues form the bark and wood of a mature stem. </li></ul>
    67. 68. <ul><ul><li>Formation of Wood </li></ul></ul><ul><ul><ul><li>Wood is actually layers of xylem. These cells build up year after year. </li></ul></ul></ul>Secondary Growth of Stems Wood Bark
    68. 69. <ul><li>As woody stems grow thicker, older xylem cells near the center of the stem no longer conduct water. </li></ul><ul><li>This is called heartwood. Heartwood supports the tree. </li></ul>Secondary Growth of Stems Xylem: Heartwood
    69. 70. <ul><li>Heartwood is surrounded by sapwood. </li></ul><ul><li>Sapwood is active in water and mineral transport. </li></ul>Secondary Growth of Stems Xylem: Sapwood
    70. 71. <ul><ul><li>Formation of Bark </li></ul></ul><ul><ul><ul><li>On most trees, bark includes all of the tissues outside the vascular cambium — phloem, the cork cambium and cork. </li></ul></ul></ul>Secondary Growth of Stems Bark
    71. 72. Secondary Growth of Stems <ul><li>The vascular cambium produces new xylem and phloem, which increase the width of the stem. </li></ul>Vascular cambium
    72. 73. Secondary Growth of Stems <ul><li>The phloem transports sugars produced by photosynthesis. </li></ul>Phloem
    73. 74. <ul><li>The cork cambium produces a protective layer of cork. </li></ul>Secondary Growth of Stems Cork cambium
    74. 75. <ul><li>The cork contains old, nonfunctioning phloem that protects the tree. </li></ul>Secondary Growth of Stems Cork
    75. 76. 23–4 Leaves
    76. 77. Leaf Structure <ul><ul><li>The structure of a leaf is optimized for absorbing light and carrying out photosynthesis. </li></ul></ul>
    77. 78. Leaf Structure <ul><li>To collect sunlight, most leaves have thin, flattened sections called blades. </li></ul>Blade Stem Bud Petiole Simple leaf Compound leaf Leaflet
    78. 79. Leaf Structure <ul><li>The blade is attached to the stem by a thin stalk called a petiole. </li></ul>Blade Stem Bud Petiole Simple leaf Compound leaf Leaflet
    79. 80. Leaf Structure <ul><li>Simple leaves have only one blade and one petiole. </li></ul>Blade Stem Bud Petiole Simple leaf Compound leaf Leaflet
    80. 81. Leaf Structure <ul><li>Compound leaves have several blades, or leaflets, that are joined together and to the stem by several petioles. </li></ul>Blade Stem Bud Petiole Simple leaf Compound leaf Leaflet
    81. 82. Leaf Structure <ul><li>Leaves are covered on the top and bottom by epidermis. </li></ul>Epidermis Epidermis
    82. 83. Leaf Structure <ul><li>The epidermis of many leaves is covered by the cuticle. </li></ul>Epidermis Epidermis Cuticle
    83. 84. Leaf Structure <ul><li>The cuticle and epidermal cells form a waterproof barrier that protects tissues inside the leaf and limits the loss of water through evaporation. </li></ul><ul><li>The veins of leaves are connected directly to the vascular tissues of stems. </li></ul>
    84. 85. Leaf Structure <ul><li>In leaves, xylem and phloem tissues are gathered together into bundles that run from the stem into the petiole. </li></ul><ul><li>In the leaf blade, the vascular bundles are surrounded by parenchyma and sclerenchyma cells. </li></ul>
    85. 86. Leaf Structure <ul><li>All these tissues form the veins of a leaf. </li></ul>Xylem Phloem Vein
    86. 87. Leaf Functions <ul><ul><ul><li>Most leaves consist of a specialized ground tissue known as mesophyll. </li></ul></ul></ul>Palisade mesophyll Spongy mesophyll
    87. 88. Leaf Functions <ul><li>The layer of mesophyll cells found directly under the epidermis is called the palisade mesophyll. These closely-packed cells absorb light that enters the leaf. </li></ul>Palisade mesophyll
    88. 89. Leaf Functions <ul><li>Beneath the palisade mesophyll is the spongy mesophyll, a loose tissue with many air spaces between its cells. </li></ul>Spongy mesophyll
    89. 90. Leaf Functions <ul><li>The air spaces connect with the exterior through stomata. </li></ul><ul><li>Stomata are openings in the underside of the leaf that allow carbon dioxide and oxygen to diffuse in and out. </li></ul>Stoma
    90. 91. Leaf Functions <ul><li>Each stoma consists of two guard cells that control the opening and closing of stomata by responding to changes in water pressure. </li></ul>Guard cells
    91. 92. Leaf Functions <ul><ul><li>Transpiration </li></ul></ul><ul><ul><ul><li>The surfaces of spongy mesophyll cells are kept moist so gases can enter and leave the cells easily. </li></ul></ul></ul><ul><ul><ul><li>Water evaporates from these surfaces and is lost to the atmosphere. </li></ul></ul></ul>
    92. 93. Leaf Functions <ul><li>Transpiration is the loss of water through leaves. Transpiration pulls water from the roots through the vascular tissues and out the leaves. </li></ul>
    93. 94. Leaf Functions <ul><ul><li>Plant leaves allow gas exchange between air spaces in the spongy mesophyll and the exterior by opening their stomata. </li></ul></ul><ul><ul><li>Plants keep their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water. </li></ul></ul>
    94. 95. Leaf Functions <ul><li>Guard cells are specialized cells that control the stomata. </li></ul><ul><li>Stomata open and close in response to changes in water pressure within guard cells. </li></ul>
    95. 96. Leaf Functions <ul><li>When water pressure within guard cells is high, the stoma open. </li></ul>
    96. 97. Leaf Functions <ul><li>When water pressure within guard cells decreases, the stoma closes. </li></ul>
    97. 98. Leaf Functions <ul><li>Plants regulate the opening and closing of their stomata to balance water loss with rates of photosynthesis. </li></ul><ul><li>Stomata are open in daytime, when photosynthesis is active, and closed at night, to prevent water loss. </li></ul><ul><li>In hot, dry conditions stomata may close even in bright sunlight, to conserve water. </li></ul>
    98. 99. 23-5 Transport in Plants
    99. 100. Water Pressure <ul><ul><ul><li>Xylem tissue forms a continuous set of tubes that runs from the roots through stems and out into the spongy mesophyll of leaves. </li></ul></ul></ul><ul><ul><ul><li>Active transport and root pressure cause water to move from soil into plant roots. </li></ul></ul></ul><ul><ul><ul><li>Capillary action and transpiration also are needed to transport water and minerals. </li></ul></ul></ul>
    100. 101. Water Pressure <ul><ul><li>The combination of root pressure, capillary action, and transpiration provides enough force to move water through the xylem tissue of even the tallest plant. </li></ul></ul>
    101. 102. Water Pressure <ul><li>Cohesion is the attraction of water molecules to each other. </li></ul><ul><li>Adhesion is the attraction between unlike molecules. </li></ul>
    102. 103. Water Pressure <ul><li>The tendency of water to rise in a thin tube is called capillary action. </li></ul><ul><li>Water is attracted to the walls of the tube, and water molecules are attracted to one another. </li></ul>
    103. 104. Water Pressure <ul><li>Capillary action causes water to move much higher in a narrow tube than in a wide tube. </li></ul>
    104. 105. Water Pressure <ul><li>Tracheids and vessel elements form hollow connected tubes in a plant. </li></ul><ul><li>Capillary action in xylem causes water to rise well above the level of the ground. </li></ul>
    105. 106. Water Pressure <ul><ul><li>Transpiration </li></ul></ul><ul><ul><ul><li>In tall plants, the major force in water transport comes from the evaporation of water from leaves during transpiration. </li></ul></ul></ul>
    106. 107. Water Pressure <ul><ul><ul><li>When water is lost through transpiration, osmotic pressure moves water out of the vascular tissue of the leaf. </li></ul></ul></ul>
    107. 108. Water Pressure <ul><li>The movement of water out of the leaf “pulls” water upward through the vascular system all the way from the roots. </li></ul><ul><li>This process is known as transpirational pull. </li></ul>
    108. 109. Water Pressure <ul><ul><li>Controlling Transpiration </li></ul></ul><ul><ul><ul><li>The water content of the leaf is kept relatively constant. </li></ul></ul></ul><ul><ul><ul><li>When there is a lot of water, water pressure in the guard cells is increased and the stomata open. </li></ul></ul></ul><ul><ul><ul><li>Excess water is lost through open stomata by transpiration. </li></ul></ul></ul>
    109. 110. Water Pressure <ul><li>When water is scarce, the opposite occurs. </li></ul><ul><li>Water pressure in the leaf decreases. The guard cells respond by closing the stomata. </li></ul><ul><li>This reduces further water loss by limiting transpiration. </li></ul><ul><li>When too much water is lost, wilting occurs. When a leaf wilts, its stomata close and transpiration slows down. This helps a plant conserve water. </li></ul>
    110. 111. Nutrient Transport <ul><ul><ul><li>Many plants pump sugars into their fruits. </li></ul></ul></ul><ul><ul><ul><li>In cold climates, plants pump food into their roots for winter storage. </li></ul></ul></ul><ul><ul><ul><li>This stored food must be moved back into the trunk and branches of the plant before growth begins again in the spring. </li></ul></ul></ul>
    111. 112. Nutrient Transport <ul><ul><li>Movement from Source to Sink </li></ul></ul><ul><ul><ul><li>A process of phloem transport moves sugars through a plant from a source to a sink. </li></ul></ul></ul><ul><ul><ul><li>A source is any cell in which sugars are produced by photosynthesis. </li></ul></ul></ul><ul><ul><ul><li>A sink is any cell where the sugars are used or stored. </li></ul></ul></ul>
    112. 113. Nutrient Transport <ul><ul><ul><li>When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of fluid in that same direction. </li></ul></ul></ul><ul><ul><ul><li>As a result, phloem is able to move nutrients in either direction to meet the nutritional needs of the plant. </li></ul></ul></ul>
    113. 114. <ul><ul><li>The pressure-flow hypothesis explains how phloem transport takes place. </li></ul></ul>Nutrient Transport
    114. 115. <ul><li>Sugars produced during photosynthesis are pumped into the phloem (source). </li></ul>Nutrient Transport Sugar molecules Movement of water Movement of sugar Phloem Xylem Source cell
    115. 116. <ul><li>As sugar concentrations increase in the phloem, water from the xylem moves in by osmosis. </li></ul>Nutrient Transport Movement of water Movement of sugar Sugar molecules Phloem Xylem Source cell
    116. 117. <ul><li>This movement causes an increase in pressure at that point, forcing nutrient-rich fluid to move through the phloem from nutrient-producing regions …. </li></ul>Nutrient Transport Movement of water Movement of sugar Sugar molecules Phloem Xylem Source cell
    117. 118. <ul><li>… . toward a region that uses these nutrients (sink). </li></ul>Nutrient Transport Xylem Phloem Movement of water Movement of sugar Sink cell
    118. 119. <ul><li>If part of a plant actively absorbs nutrients from the phloem, osmosis causes water to follow. </li></ul><ul><li>This decreases pressure and causes a movement of fluid in the phloem toward the sink. </li></ul>Nutrient Transport Movement of water Movement of sugar Xylem Phloem Sink cell