Materials: - Five toothpicks (flat kind)
- 1 Petri dish
- Over head projector
- Cup of water
- Dropper
Procedure: 1. Break five toothpicks in half but leave the parts together, and leave them in a V- shape (Figure 1, left).
2. Place the five V-shaped toothpicks in the Petri dish with their points together as in Figure 2.
3. Using the dropper, let one drop fall into the centre of the toothpick configuration.
4. Observe carefully what is happening to the toothpicks.
Explanation:
The toothpick star hook demonstrates the phenomenon of capillary action. This is when liquid rises in a narrow space such as a thin tube, or some porous material. This effect can cause the liquid to flow against the force of gravity. The same process is at work when water flows to the top of a tree. The bark of a tree resembles the toothpick in structure: hard, wooden surface that consists of xylem and phloem. It is through these vessels that water moves through the plant, and if these vessels are unbroken, water can still move through them, making the wood ‘springy’ and flexible.
This is also why cut flowers become limp when not placed it water. This phenomenon is cause by the surface tension and forces of adhesion between the liquid and the surrounding material. The water should have been absorbed via diffusion into the cell walls, filling the wood fibers and therefore making them springier (Figure 3).
Why this hook is worthwhile!This hook is worthwhile to incorporate into the beginning of a plants unit, in grade 11 biology, because it is an excellent lead in to the investigation of structures and function of plant tissues. It gets the students to access prior knowledge about plant materials and other situations where capillary action is at work. Finally it also applies a scientific concept to the real world as they see it every day at work in trees.
Grade: 11 Biology, Academic SBI3U
Strand: Plants: Anatomy, growth and function.
Specific expectation: F3.1 describe the structures of the various types of tissues in vascular plants, and explain the mechanisms of transport involved in the processes by which materials are distributed throughout a plant (e.g., transpiration, translocation, osmosis).
Quick Reply
