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Plant Structure and Function

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Presentation on theme: "Plant Structure and Function"— Presentation transcript:

1 Plant Structure and Function
Chapter 21 Plant Structure and Function

2 Specialized Tissues in Plants
Seed Plant Structure (3 principal organs) Roots Absorbs water and dissolved nutrients Anchors plants in ground Stems Support system, transport system, and defense system Leaves Main photosynthetic systems

3 Plant Tissue Systems Plants consist of three main tissue systems
Dermal: “skin” that protects against water loss and injury Vascular: “bloodstream” that transports water and nutrients throughout the plant Ground: everything else


5 Dermal Tissue Consists of a single layer of epidermal cells
Often covered with a thick waxy layer (cuticle) Guard cells: on underside of leaves regulate water loss and gas exchange

6 Vascular Tissue Xylem Phloem
Tracheid: long, narrow cells with walls that are impermeable to water Vessel element: arranged end to end; cell walls at both ends lost when cell dies Phloem Sieve elements: arranged like vessel elements and ends have many small holes Companion cells: cells that surround sieve element and aid in movement of substances in and out of cell

7 Ground Tissue Composed of cells that lie between dermal and vascular tissues Parenchyma: thin cell walls and large central vacuoles: in leaves they are packed with chlorophyll Collenchyma: strong, flexible cell walls that help support larger plants Sclerenchyma: extremely thick, rigid cell walls

8 Plant Growth and Meristematic Tissue
Plant growth occurs at meristems that are responsible for continuing growth throughout the plant’s life Meristematic tissue: undifferentiated (not yet become specialized), only plant tissue that produces new cells by mitosis Apical meristem: produce increased length at stems and roots Differentiation: development into specialized structures and functions

9 Roots Types of Roots: Taproots: primary root grows long and thick to reach water far below Earth’s surface Fibrous roots: branch to such an extent that no single root grows larger than the rest

10 Root Structure and Growth
A mature root has an outside layer, the epidermis, and a central cylinder of vascular tissue Root hairs: produce large surface area through which water can enter the plant Vascular cylinder: phloem and xylem Root cap: protects root as it forces its way through the soil (Fig 23.7)


12 Root Functions Uptake of Plant Nutrients Active Transport of Nutrients
Composition of soil determines plants present Active Transport of Nutrients Use ATP to pump mineral ions from the soil into the plant Movement into the Vascular Cylinder Osmosis and active transport cause water and minerals to move form epidermis to cortex Root Pressure Pressure allows for upward movement of water


14 Stems Stem Structure and Function: they produce leaves, branches, and flowers; hold leaves up to the sunlight: and transport substances between roots and leaves Nodes: where leaves attach Internodes: regions between the nodes Buds: undeveloped tissue that can produce new stems and leaves

15 Monocot and Dicot Systems
Monocots Vascular bundle scattered throughout the cell Phloem faces outside of cell and xylem faces the center Dicots Vascular bundles arranged in a cylinder Pith: parenchyma cells inside ring Cortex: parenchyma cells outside of ring

16 Primary Growth of Stems
Refers to growth occurring at ends of a plant Produced by cell divisions in the apical meristem. It takes place in all seed plants

17 Secondary Growth of Stems
Method in which stems grow in width In conifers and dicots, secondary growth takes place in lateral meristematic tissues called the vascular and cork cambium Vascular cambium: produces vascular tissues and increases thickness of stems Cork cambium: produces outer coverings of stems


19 Formation of Stems Formation of Vascular Cambium: Formation of Wood:
Once secondary growth begins, vascular cambium appears as thin layer between clusters of vascular tissue Formation of Wood: Heartwood: no longer conducts water (dark) Sapwood: actively conducts water (light) Formation of Bark: All of the tissues outside the vascular cambium


21 Leaves Leaf Structure: optimized for absorbing light and carrying out photosynthesis Blades: flattened sections that absorb sunlight Petiole: thin stalk that attaches blade to stem

22 Leaf Function Photosynthesis: occurs in the mesophyll in most plants (Fig 23-18) Stomata: porelike openings on underside of leaf that allow CO2 and O2 to diffuse through Guard cells: control opening and closing of stomata Transpiration: loss of H2o through leaves

23 Leaf Function (cont.) Gas Exchange: leaves take in CO2 and release O2
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

24 Transport in Plants Water Transport: the combination of root pressure, capillary action, and transpiration provides enough force to move water through the xylem tissue Capillary action: tendency of water to rise in a thin tube; works by adhesion (attraction between unlike molecules)

25 Transport in Plants (cont.)
Transpiration: major force in water transport to topmost branches and leaves Controlling transpiration: controlled by a series of feedback mechanisms Transpiration and wilting: high transpiration rates can lead to wilting


27 Nutrient Transport Functions of Phloem Movement From Source to Sink
Carry out the seasonal movement of sugars within the plant Movement From Source to Sink Pressure-flow hypothesis: Source: where sugars are pumped into xylem Sink: region that utilizes the sugars When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of fluid in the same direction


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