Have students pour potting soil into two plastic cups, and plant any seed desired. Tell the students that to water one plant as needed, and leave the other plant without water. Place both of the cups in a sunny area and let the students document the plants' progress each day. After the watered plant begins to grow, ask the students why the other plant did not grow as the watered one did. You can also choose to water both plants, but only place one of the cups in the sun and have the students document what they observe.
Seeds hold embryos that burst out of the seed coats during germination. Have students soak seeds in water, and place them in a warm sunny area. Let students observe the seeds each day and document any changes in growth. As the seeds absorb the water, enzymes are activated which increases respiration, causing plant cells to duplicate. The root pushes through the seat coat first so that it can plant itself deep into the soil to continue absorbing water for the growing embryo.
Make a rain gauge by cutting the top off of a clear plastic bottle. Remove any labels from the bottle. Starting from the bottom of the bottle, have students measure and mark in one-inch increments up to 12 inches with a permanent marker. Use a heavy duty staple gun to attach the bottle at the top of a three-foot wooden dowel. Take the assembled rain gauge outside, and stick the dowel one foot into the ground. After a rainfall, let the students measure the amount of rain that has fallen.
Let students make a tornado by emptying two clear plastic bottles and removing any labels. Fill two-thirds of one bottle with water. Add two ounces of colored lamp oil to the bottle of water for color. Turn the empty bottle upside down, and place it on top of the nozzle of the water-filled bottle. Securely attach both nozzles together with duct tape. Turn the contraption over and swing the bottle in a fast circular motion a few times to get the water swirling. It will create a vortex as it drains into the empty bottle below.