Terrariums are often used to get children interested in gardening, but they also can be a powerful illustration about the importance of plants. You will need two empty 2-liter soda bottles, potting soil, gravel, and several small plants and live bugs, such as flies or crickets. Cut the top off of each bottle and fill it with a layer of gravel, then a layer of potting soil. In one bottle, plant your small plants. Leave the other terrarium empty of plants. Tape the bottles back together and add a few bugs to each one. Tightly close the lids. Over the next several days, have students watch to see what happens. The bugs in the bottle with plants will survive, while the bugs in the other bottle will likely not. This illustrates how plants clean the air we breathe so we are able to survive.
For a root exploration experiment, you will need two large plastic cups, food coloring, and two stalks of celery or two individual white daisies. Fill each cup three-fourths of the way with water and add two or three drops of food coloring to one of the cups. Dark colors will work best with this experiment. Place one celery stalk or daisy in each cup. Have the students watch to see what happens over the next two or three days. One celery stalk or daisy will turn the color of the water, which illustrates the importance of keeping soil clean and pure.
For a smog in a jar experiment, collect two large jars, aluminum foil, ice cubes, matches, two small pieces of paper, potting soil and small plants. Form two pieces of aluminum foil into lids for the jars, and place ice cubes on each piece. Rinse the inside of each jar with water. Quickly place a shallow layer of potting soil inside one of the jars and carefully add your small plants. Leave the other jar empty. Light a piece of paper on fire with a match and drop it into the first jar. Cover it with the foil lid. Repeat for the other jar, working as quickly as possible. The smog will sit at the bottom of the jar. Watch to see if the smog disappears in the jar with the plants, which illustrates how plants help clean the air.
The dirty water experiment will illustrate the importance of clean water for the survival of earth's plant life. You will need two potted plants, a container of clean water and a container of dirty water. Make the water dirty by adding bits of trash, motor oil or bleach. Keep the dirty water away from students at all times. Water the plants once a day over a period of several days. Have the students note what happens to the plant that is watered with polluted water. Discuss how keeping water clean impacts the earth's flora and how that affects the human population.