The biosphere is home to a diverse population of living things - including human beings - that depend on each other. For example, most animals breathe in oxygen and breathe out carbon dioxide. In turn, most plants use carbon dioxide to make energy, and one of the end products is oxygen. This is one of the major relationships between living things on the planet. It is also a clear demonstration of why biodiversity is good for the planet.

Try making your own mini-biosphere.

1. Clean and dry the 2-liter bottle. Cut off the top of the bottle, about four inches (10 cm) from the top. Set aside the top for later.

2. Fill the bottom of the bottle with about six inches (15 cm) of soil. Sprinkle the grass seed on soil. Add about one more inch (2 cm) of soil over the seed.

3. Plant your small plants. Add half a cup (100 cc) of water.

4. Add earthworms and snails.

5. Position the lamp about a foot (30 cm) away from the bottle, and shine it on your mini-biosphere. Turn the lamp on during the day, and off at night. If you have a timer switch, set it to turn on for 12 hours and off for 12 hours.

6. Make predictions about your mini-biosphere. How quickly do you think the various plants will grow? Do you think the environment is enough to keep all the earthworms healthy?

7. Measure the height of the grass each day. Count the number of living earthworms or snails.

1. Draw a diagram to show the relationships between all of the living things in your mini-biosphere.

2. Make more mini-biospheres. What happens if one of the biospheres has more light? Less light? What happens if you start off with fewer types of plants? More types of plants?