Looking for a good middle school science fair project, or projects for the classroom? Plants are great for simple experiments that yield great results. Plant experiments take time, but they're inexpensive and take up little space. Give some of these "green" experiments a try:
Duckweed is a tiny, floating water plant found in ponds. These plants can be used to test the effects of pollution. Let a bucket of tap water sit out for 24 hours to let the chlorine evaporate. Mix up a standard solution of any water-soluble plant fertilizer, then mix 10 parts of the dechlorinated water with 1 part of the fertilizer. Pour the mixture into petri dishes or clear plastic cups. Add ten duckweed plants to each cup. Choose a pollutant that you want to test and add a small amount to half of the cups. Try things that people sometimes pour down street drains that they shouldn't, such as used motor oil or garden chemicals. Use small amounts to simulate how diluted the chemical would be by the time it reaches a stream. Cover the cups or dishes to prevent evaporation and observe for several weeks (add water if needed). Count the number of individual duckweed plants in the cups daily.
Transpiration is the evaporation of water from the surface of a leaf, which draws water from the roots all the way to the top of the tree. How much water does one tree pull from the ground ever hour? Here is a simple way to find out.
One way is to enclose several leaves that are still attached to a tree in a large plastic bag. Choose a leafy twig that is on the shady side of the tree on a dry day. Use a twist tie to fasten the bag around the twig that the leaves are attached to. Leave in place for an hour. At the end of the hour, see if there is any water in the bag. If so, remove the bag and pour the water into a measuring cup or a graduated cylinder. Divide the amount of water by the number of leaves in the bag to get the amount of water transpired per leaf. Then estimate the total number of leaves on the tree. Multiply this amount by the amount of water transpired per leaf, and you'll have a pretty good estimate of the total amount of water that the tree transpired. Try this with different species of tree to see if different trees transpire at different rates.
EFFECTS OF ELEVATED CARBON DIOXIDE
News of global climate change has a lot of people asking what will happen to plants when carbon dioxide levels in the atmosphere are high? Find out with a simple experiment. Plant bird seed mix or radish seeds in small pots. Let the seeds germinate and the plants get off to a good start. Then cover each pot loosely by placing each in a gallon-sized zipper-type plastic bag. Seal the bags, but place a straw in the zipper to allow some air in and out. For your control group, leave just as they air with regular air. For the experimental group, add carbon dioxide to the air. Mix one-half teaspoon of baking soda with two teaspoons of vinegar in a small cup and place the cup in one of the experimental bags. Do the same with the remaining bags. The vinegar and baking soda will release carbon dioxide. Repeat the application of carbon dioxide every two days, and watch your plants for several weeks. Is there any difference in growth rates or appearance? How will you measure the effects?
PLANT GROWTH: LIGHT, GRAVITY, ROOTS, AND SHOOTS
How do plant shoots "know" to grow up and roots "know" to grow down? To find out, soak some bean or corn seeds in water overnight. Fold several layers of paper towel so that they will fit inside of a sandwich-sized zipper-type plastic bag. Moisten the towel and place the seeds in a row across the middle of the towel. Lay a piece of facial tissue over the seeds and press to hold them in place. Rinse the plastic bag with vinegar followed by water to help prevent mold, then place the seeds on their paper inside. Tape this bag in a sunny window. Prepare a similar bag and tape it inside of a closet door. Observe for several days until the seeds germinate. Which way to the roots go? Which way do the shoots go? Now turn the baggies one-quarter turn so that the roots and shoots are horizontal and watch for several more days. Do the roots or shoots turn? In what direction? What effect does light have on the direction that roots and shoots grow? What is the effect of gravity?