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