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Chapter 23 Lecture- Roots, Stems, Leaves
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Chapter 23 Lecture- Roots, Stems, Leaves

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Chapter 23 Lecture for Lab Biology

Chapter 23 Lecture for Lab Biology

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