Children can build their very own mini-ecosystem in a 2 liter pop bottle to learn how plants grow. These systems do not require any care after they are assembled, and children can watch the roots of the various plants growing into the soil. They'll be able to chart the daily growth and progress of the plants, and by the end will have a clearer understanding of how this part of nature works.
Cut the top off an empty 2 liter pop bottle. Make the cut horizontal and cut where the bottle first starts to curve inward to form the neck.
Place 3 inches of good potting soil inside the bottle. Relia.net recommends growing bean and grass seed in your bottle.
Create a hole 1 inch deep in the dirt using the eraser end of a pencil. Place a bean seed inside. Create enough holes for each bean seed. Place the seeds in the bottom of the holes and cover them with dirt.
Sprinkle the grass seed over the top of the dirt. Relia.net recommends using a fork to lightly mix up the top layer of dirt so it covers the grass seeds but doesn't bury them too deep.
Lightly sprinkle water over the soil until it is damp and moist. Make sure all the soil is wet but not completely soaked. Add water every few minutes until you can see the water has soaked through to the bottom but the soil is still dry enough to stick together.
Place the top of the bottle that you cut off upside down into the rest of the bottle. Tape the edges to hold it in place. Place the bottle in a sunny area and observe it daily. You do not need to do anything else to the bottle. Plants will begin to grow over time.