Teaching Objectives

Beginning concept

• The upward movement of water in plants is due partly to capillary action.

Time required for exercise

·1 hour

Materials needed.

This exercise requires the following:

• 13-15 day old Wisconsin Fast Plants (flowering)
• small containers
• green or blue food coloring
• water
• razor blade or scissors

Exploratory questions.

Ask your students questions and discuss ideas they might have, such as:

• How do water and minerals move from the roots of Fast Plants to the leaves?
• Will water rise in a narrow tube?

EXPLORATION

1.Add 10-15 drops of food coloring to a cup of water.

2. Cut a Fast Plant at the stem with a diagonal transverse cut and place the cut end in the cup of food coloring solution.

3. Observe the plant for evidence of food coloring in the stem and flowers every ten minutes.

ACCOMPANYING ACTIVITY

The capillary action of water used in the water reservoir/wick system with Fast Plants can be demonstrated easily. Cut paper towels into strips six inches long.Mark lines on the strips at the midpoint with water-soluable magic markers. Place one end of the strip in a shallow container of water such that the mark is at the edge of the container and above the water level. Observe what happens to the mark over the next fifteen minutes.

Background Information for the Teacher

Water and minerals absorbed by roots of a plant move up the stem to the leaves, while sugar formed by photosynthesis moves from leaves to stems and the underground root system. Plants have tissues specialized for conduction (the vascular system). The part of the vascular system which conducts water and minerals upward is the xylem. The xylem tissue forms narrow tubes in which capillary action helps move water upward.

Other factors involved in upward movement of water are osmotic pressure, transpiration pull and cohesion of water molecules. Osmotic pressure contributes to upward movement because water moves from areas of higher concentration (soil) to areas of lower concentration (roots). Transpiration is the loss of water from leaves. Transpiration pull is the pulling up of water into the leaf to replace the water lost by transpiration or used by photosynthesis. Finally, water molecules are polar (have a positive and negative end) and are attracted to each other as one molecule's positive and attracts the negative end of the next water molecule.

References:

Suzuki,D. and B.Hehner,Looking at Plants,Stoddart Publishing Co.,Ltd.,Toronto,Canada,1985.A tour though the plant world in clear and interesting language for students, plus short and long term projects.