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SOS Classroom

Grades 6-8 Biology: Dying Flowers

Overview:
Use colored dyes to follow water up a plant’s stem and into the petals (transpiration).

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Equipment:
1. White flowers – Queen Anne’s Lace or white carnations work best.
2. Water-soluble food coloring, from the local grocery store – blue and red work best.
3. Container.
4. Knife to split the stem if you want to experiment further.

Safety:
Be careful with the knife if you cut the stem.

How to do the experiment:
1. Add food coloring + water to the container in which you’ll place the white flowers. Put the flowers in the container.
2. Wait 6-12 hours, and observe. For a better idea of what goes on, check back every few hours to note the level of the food coloring in the plant. Depending on the length of the stem, the white petals should ultimately turn the color of the dye added to the water.
3. If you want to experiment further, split the stem into 2, or into thirds, and place each section in a container with different food coloring (white carnations with blue/red/yellow produces an interesting effect. Observe results.

Explanation:
The leaves and some petals of plants contain many small pores, called stomata or stomates (singular: stoma or stomate). Water evaporates through these pores. As it does so, the plant draws water through its stem, and ultimately from its roots via the surrounding soil (or from the water in the vase). This process of water loss from the plant is called transpiration. Water movement through the plant occurs in xylem, hollow cells stacked end to end to form tubes. In leaves and thin stems, the xylem occurs in vascular bundles that also contain phloem, which transports organic compounds throughout the plant. In leaves, vascular bundles are termed veins. Blue or red dye is very good for outlining the xylem in the plant as it draws the water + dye up the stem. You can see it quite clearly if you cut the stem and look at it in cross-section.

Send us pictures of your unusual colored plants.

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