23.1 Specialized Tissues in Plants

The three principal organs of seed plants are roots, stems, and leaves.

Dermal tissue is the protective outer covering of a plant. Vascular tissue supports the plant body and transports water and nutrients throughout the plant. Ground tissue produces and stores sugars and contributes to the physical support of the plant.

Meristems are regions of unspecialized cells in which mitosis produces new cells that are ready for differentiation.

• epidermis (665)

• parenchyma (667)

• lignin (666)

• collenchyma (667)

• vessel element (666)

• sclerenchyma (667)

• sieve tube element (666)

• meristem (667)

• companion cell (666)

• apical meristem (668)

23.2 Roots

A mature root has an outside layer, called the epidermis, and also contains vascular tissue and a large area of ground tissue.

Roots support a plant, anchor it in the ground, store food, and absorb water and dissolved nutrients from the soil.

• root hair (670)

• vascular cylinder (670)

• cortex (670)

• root cap (670)

• endodermis (670)

• Casparian strip (672)

23.3 Stems

Aboveground stems have several important functions: Stems produce leaves, branches, and flowers; stems hold leaves up to the sun; and stems transport substances throughout the plant.

Primary growth of stems is the result of elongation of cells produced in the apical meristem. It takes place in all seed plants.

In conifers and dicots, secondary growth takes place in meristems called the vascular cambium and cork cambium.

• node (675)

• vascular cambium (677)

• bud (675)

• cork cambium (677)

• vascular bundle (675)

• heartwood (678)

• pith (675)

• sapwood (678)

• primary growth (676)

• bark (679)

• secondary growth (676)

23.4 Leaves

The structure of a leaf is optimized to absorb light and carry out photosynthesis.

Plants maintain homeostasis by keeping their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water.

• blade (680)

• spongy mesophyll (681)

• petiole (680)

• stoma (681)

• mesophyll (680)

• transpiration (681)

• palisade mesophyll (681)

• guard cell (682)

23.5 Transport in Plants

The combination of transpiration and capillary action are the major forces that move water through the xylem tissues of a plant.

Changes in nutrient concentration drive the movement of fluid through phloem tissue in directions that meet the nutritional needs of the plant.

• adhesion (686)

• capillary action (686)

• pressure-flow hypothesis (687)

Think Visually Make a flowchart of the tissues through which water passes, from where it enters a plant at the root until it exits the plant through the leaves. Use the following terms in your flowchart: epidermis, cortex, endodermis, xylem, stomata.