Life Cycle - Plants (3B)
Pre Lab

   
OBJECTIVES:
  • Exploring plant characteristics.
  • Determining which plants have a vascular system.

VOCABULARY:

  • nonvascular
  • vascular
  • phloem
  • xylem
MATERIALS:
  • celery stalks or carnation
  • beakers
  • food coloring
  • knife

Students learn about xylem and phloem using celery.


Rice plants are surrounded by water, but they still have to move water to its leaves. 
BACKGROUND:

Vascular plants are plants that have specialized conducting tissue and are usually grouped as tracheophytes and include the ferns, horsetails, angiosperms (flowering plants) and gymnosperms (pine-like trees). Thallophytes (water type plants) and bryophytes (mosses) do not have true roots, stems, and leaves and possess no specialized system for the conduction of food and water from one part of the plant to another. Plants that have a vascular system are larger and able to cope with a "land situation." There are no plants with a vascular system in a total water environment because the water provides the nutrients the plants require, so they do not have to "conduct" these substances.

Woody stems are mostly secondary xylem (wood) surrounded by bark. The xylem may include heart-wood and sap-wood. Heart-wood is dead and non-functional. The sap wood is functional and has living parenchymal cells.

PROCEDURE:

  1. Give each group of children a piece of celery (cross section) and have them place a drop of food coloring on the top. The celery should show color only in small dots. These are part of the xylem tissue that is responsible for water transport.
       

  2. Discuss with the students the different types of specialized conducting cells of vascular plants namely, the phloem and the xylem. Explain to students that phloem tissue conducts food produced in the leaves to the rest of the plant while xylem tissue conducts water and mineral salts from the roots. The xylem tissue also gives strength to the stem.

The xylem is the structure to the extreme left; and the phloem is the center red area.

  1. You can dramatically demonstrate the "power" of xylem tissue by using a celery stalk and/or carnation. For the celery stalk cut the bottom of the stalk (as in the diagram) and place one end in one food color and the other in a different color. Within a day or so, the water with the color will migrate upward and the celery will be two colors. For the carnation, trim the stem and place it in colored water. The water will migrate upward through the xylem tissue and color the petals of the carnation.

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