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Section 23-1: Specialized Tissues in Plants
The three principal organs in seed plants are roots, stems, and leaves.
Plants consist of three tissue systems: dermal tissue, vascular tissue, and ground tissue.
Meristematic tissue is the only plant tissue that produces new cells by mitosis.
Vascular tissue contains several different cell types. Xylem consists of tracheids and vessel elements, and phloem consists of sieve tube elements and companion cells.
Section 23-2: Roots
The two main types of roots are taproots, found mainly in dicots, and fibrous roots, found mainly in monocots.
A mature root has an outside layer of epidermal cells and a central cylinder of vascular tissue separated by a large area of ground tissue called the cortex.
Roots anchor a plant in the ground and absorb water and dissolved nutrients from the soil.
Section 23-3: Stems
Stems have three important functions: they produce leaves, branches, and flowers; they hold leaves up in the sunlight; and they transport various substances between roots and leaves.
In monocots, vascular bundles are scattered throughout the stem. In dicots and most gymnosperms, vascular bundles are arranged in a cylinder.
In all seed plants, primary growth of stems is produced by cell divisions in the apical meristem.
In conifers and dicots, secondary growth takes place in lateral meristematic tissues called the vascular cambium and cork cambium.
Section 23-4: Leaves
The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.
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.
Section 23-5: Transport in Plants
Root pressure, capillary action, and transpiration work together to move water through the xylem tissue of even the largest plant.
When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of water in that same direction. As a result, phloem is able to move nutrients in either direction to meet the nutritional needs of the plant.