Deserts - Activity

Here is a hands-on activity you can try at home.
This activity will demonstrate how some cactus plants are able to store water.

Materials:
Plain white paper
1-gallon plastic food bag (a grocery store produce bag will work well for this)
Tape

Watch the video to see how to complete this activity. You can always watch the video again if you need to.



Procedure:
1) Fold the piece of white paper into a fan, beginning at one of the short ends. Each fold should be about 1/2-inch wide.

2) Fold the plastic bag into thirds.

3) Lay the folded bag on top of the paper fan. The bottom of the bag should line up with the edge of the paper. Tape the bottom of the bag to the edge of the paper.

4) Wrap the paper around the bag so it forms a cylinder. Tape up the ends of the paper.

5) Stand the paper cylinder on a table with the open end of the bag facing up. Make sure you observe the size of the cylinder before moving on.

6) Open up the top of the bag and blow into the bag while holding it with your hand. Keep the air inside the bag by squeezing the top closed with your hand. Now, observe the size of the cylinder again. How has it changed?

7) Let the bag open up and then use your hands to gently squeeze the paper pleats back into place. Observe the size of the cylinder one more time. How has it changed?

8) Please write about your observations in the comments section of this blog post (how did the cylinder size change at each point?) Write at least two or three sentences telling what you saw and learned.

How this activity is like a cactus:
This shows how a cactus holds extra water. The saguaro cactus (look at the photo below) is able to grow very tall. These cacti have trunks that have pleats, just like the paper in the activity. A cactus that is 20-feet tall is able to store over 100 gallons of water! When the trunk fills with water, the water pushes against the sides of the plant causing the pleats to unfold.
A cactus can increase by as much as 20% as it fills with water. This ability to hold water allows the cacti to live through long periods of drought (VanCleave, 1996).

References
Backe, B. (n.d.). Saguaro cactus [Photograph]. Retrieved November 4, 2008 from http://student.britannica.com/eb/art-73109/Saguaro-cactus

VanCleave, J. (1996). Ecology for every kid: Easy activities that make learning science fun. San Francisco: Jossey-Bass.