Xylem

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  eBook - ePub

  The Handy Biology Answer Book

  • Patricia Barnes-Svarney, Thomas E. Svarney(Authors)
  • 2014(Publication Date)
  • Visible Ink Press

    (Publisher)

  Plants have three types of tissue, each with its own function. They include the dermal tissue, which includes the epidermis, and the vascular tissue, which includes the Xylem and phloem. The following gives more detail about these tissues:

  Epidermis —Several types of specialized cells occur in the epidermis (outside), including guard cells and root hairs. Flattened epidermal cells—one layer thick and coated by a thick layer of cuticle—cover all parts of the primary plant body.

  Xylem —Xylem (from the Greek term xylos , meaning “wood”) is the main water- and mineral-conducting tissue of plants and consists of dead, hollow, tubular cells arranged end to end. The water transported in Xylem replaces water that is lost through evaporation (through the leaf’s stomata). Water-conducting cells come in two types. Water flows from a plant’s roots up through the shoot via pits in the secondary walls of cells called tracheids; vessel element cells have perforations in their end walls that allow the water to flow between cells.

  Phloem —The phloem conducts foods for the plant—including carbohydrates (mainly sucrose), hormones, amino acids, and other substances for the plant’s growth and nutrition. The two kinds of cells in the phloem (from the Greek term phloios , meaning “bark”) are sieve cells (in the seedless vascular plants and gymnosperms) and sieve-tube members (in angiosperms). Both are elongated, slender, tubelike cells arranged end to end with clusters of pores at each cell junction. Sugars (especially sucrose), other compounds, and some mineral ions move between adjacent food-conducting cells.

  What are some of the major plant pigments?

  Four major plant pigments give a plant its green color (for example, stems and leaves) and other colors (for example, certain colorful flowers). The following lists the pigments and where they are found (for more about plant pigments, see this chapter):

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