Chapter 21 Plant Structure and Function. Specialized Tissues in Plants Seed Plant Structure (3 principal organs) Seed Plant Structure (3 principal organs)

Chapter 21

Plant Structure and Function

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

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

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

Vascular Tissue

Xylem 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

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

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

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

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)

Root Functions

Uptake of Plant 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

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

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

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

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

Formation of Stems

Formation of Vascular Cambium: 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

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

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

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

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)

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

Nutrient Transport

Functions of Phloem 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