Grade Level: 4th-8th grade Activity Time: 30-45 minutes Subject Area: Biological Science Botany Objectives: Students will: View PowerPoint presentation of common desert plants Do a hands-on activity demonstrating plant adaptations background: The Sonoran Desert is a rugged place: summer temperatures can reach 120 degrees, rainfall averages less than 4 inches in some places, and there are long periods months at a time without rain. But of all the North American deserts, the Sonoran is both the mildest and the wettest, and that makes it the greenest of our deserts! Plants here are adapted to two seasons of rain and in places like Saguaro National Park, they can enjoy as much as 12 inches of rainfall. Because of this, and its many life zones, Saguaro National Park has more than 600 species of plants. vocabulary: ADAPTATION A character, physical or biological, that allows a plant or animal to live successfully in their environment. PHOTOSYNTHESIS The process in which green plants produce energy for growth and living by combining elements from water and carbon dioxide using sunlight. materials: Desert Plants PowerPoint presentation or PDF Pieces of 5 x 5 green paper Green crayons These ideal desert conditions are still difficult, which accounts for the unusual adaptations of these plants from tiny cacti that look like spiny rocks to the towering, many-armed saguaro. The subtropical climate and bizarre plants bring visitors from all over the United States and the world to discover a landscape that is unlike anything else in this country. 1
introduction: This activity builds on the identification techniques of the Classroom Classification lesson by focusing on specific characters of desert plants. Looking at these plants in detailed photographs and using a simple hands-on model allows us to see how each plant has changed its leaves to suit it to life in a desert environment. These changes are important adaptations to desert living. Activity: You can use the first three PowerPoint slides to discuss the conditions that plants must endure when living in the Sonoran Desert. Changes in the leaf structure indicate one way that plants have adapted to desert conditions. Many students will be familiar with maple leaves. (There are even maple trees at high elevations in the Sonoran Desert!) Hand out the green pieces of paper and introduce them as a model of a leaf. In fact, the paper is about the same size and thickness as a maple leaf. In the activity, the students will change their leaf model to match the identifying adaptation of the plants in the PowerPoint slides. Now proceed to the pictures of species of desert plants in the PowerPoint. You can discuss the pictures, factoid, and research question for each. Then change the paper model of a leaf to reflect the plant s adaptation using the included, Teacher s Key to Plant Adaptation Model. Prep: You will need to be able to view the Desert Diversity PowerPoint presentation, or print-outs, in order to do the activity. Also, prepare a 5 x 5 piece of green paper for each student. (Green copier paper works best, but construction paper is okay too.) Provide green wax crayons for students to use. 2
Teacher s Key to Plant Adaptation Model 1. PALO VERDE TREE: Tear off the SMALLEST possible piece from the corner of the green paper leaf model. Compare to the photograph by holding the bit of paper on your finger. Palo Verde leaves are so small that they lose very little water in the hot desert sun. But because they are so small, the tree gets ¾ of its energy (from photosynthesis) through its green bark. That is not very efficient, so palo verde trees grow slowly the one in the picture is more than 100 years old. Research answer: Palo verde means green stick. 2. CREOSOTEBUSH: Use the green crayon to color an oval, about the size of your pinky fingernail, with the WAX CRAYON on the paper. Compare to the leaves in the photograph. Creosotebush leaves are much large than palo verde leaves, but they are protected from the harsh sun by some of the same thing you just put on the paper: WAX. Scientists have found nearly fifty different waxes and oils on the leaves of the creosotebush. You can see and feel this greasiness up close, and you can smell it by rubbing the leaves or blowing on them. These special oils have made this a valuable medicinal plant for centuries. Research answer: Creosote is a liquid preservative. 3. MORMON TEA: Put the paper away in a desk or pocket Mormon Tea has no leaves! Look at the stems shown in the photograph. Mormon Tea is a plant that does not bear leaves. Instead ALL of its growth and energy production through photosynthesis is produced by its many green stems. This is a good strategy for life in dry areas so there are a number of species in the western states. Research answer: Pines, firs, spruces are common cone-bearing plants in the United States. 4. JOJOBA: Fold the paper in half, then in half again (making a smaller square), then in half once more. Now hold the leaf model vertically, perpendicular to the light. The paper model is now approximately the size and width of the leaves in the photograph. Jojoba leaves have two adaptations to arid climate. First, they are thick and leathery so they can store moisture inside without loss to the hot air. Secondly, the leaves of jojoba are oriented up and down so that they avoid the hottest sunlight while taking advantage of the sun in the early morning and evening. Research answer: Jojoba oil is widely used in shampoos. 3
Teacher s Key to Plant Adaptation Model 5. OCOTILLO: Keep the leaf model paper the same size, but imagine that it is only one sheet thick. Now hold the model out at the edge of your finger and thumb (like a leaf connected to a twig). On a signal, drop the leaf to the floor or ground. In the picture note the leaves and the thorny twig section. Ocotillo has a truly remarkable desert adaptation it only has leaves when it rains. One inch of rain, no matter when it arrives, is enough to grow new leaves on the plant. When the desert dries out again, the leaves fall off and the plant looks like a bunch of thorny dead sticks coming out of the ground. This can happen 6 or 7 times in a year. If rare fall rains bring out ocotillo leaves, they may turn brilliant colors just like maples! Research answer: Ocotillo means little torch (for its red flowers). 6. YUCCA: Unfold the paper model, then fold once in half. Fold in half again, but lengthwise. Then fold over the ends to make a triangular point. Compare to the thick, pointed leaves in the photograph. Yuccas and agaves are members of a plant family that is closely identified with American deserts. Unlike the more familiar cacti, agave family members are ALL LEAF! The leaves of yucca are thick and hard and store water inside to help the plant get through tough times. Eventually this water will be used in growing flower stalks, many times during the plant s long life. Research answer: Yucca extracts are also used in shampoos. 7. AGAVE: Unfold the paper model. Now fold it half to form a triangle. Fold in half to form a smaller triangle. Fold in half once more to form a smaller triangle. Then re-open the paper part way to form a gutter shape. Look at the spiny leaves shown in the photograph. Agave s leaves are tipped and edged with spines to keep animals from eating them. The leaves are shaped like rain gutters, directing all rainwater to the center of the plant and down into its roots. The leaves are also very thick and leathery and filled with moisture. This moisture is used to grow a flower stalk only once in the plant s life. Research answer: A species of agave is grown to produce tequila. 8. SAGUARO CACTUS: Unfold the paper. Now roll it up as tightly as possible to form a long cylinder. Gently poke your neighbor with the model. Look at the close-up photo of saguaro cactus spines. Although some cactus plants have leaves, all desert species have spines instead. Spines are modified leaves that protect the plant by offering shade, insulation, and protection from grazing animals all without losing water. Desert cacti get their energy from photosynthesis in their green skin. Research answer: Saguaro blossom is the Arizona state flower. 4
Wrap UP: The final slide in the PowerPoint presentation shows Brittlebush, a very common plant at Saguaro National Park that is most noticeable in spring after good winter rains when each bush sports dozens of big yellow, daisy-like flowers. This species is meant as a challenge to students: looking at the pictures you can see two adaptations of brittlebush. The first is pretty obvious like ocotillo, brittlebush sheds its leaves in dry seasons (unlike brittlebush, ocotillo leaves do not reappear so easily). But brittlebush leaves, when present, are quite large and not protected by leathery surface or waxy covering. Instead, as indicated by the Wet Season picture, they are covered with a white gloss. This is actually a felt-like blanket of tiny white hairs. The hairs reflect harsh sunlight off the leaf AND hold moisture on the leaf when it rains or on damp mornings. Virtually every desert plant, except those with roots that reach perennial groundwater, has adaptations for desert living. The paper leaf model is a good way to put your brain in adaptation mode. resources: For deserts from Pima Community College: http://wc.pima.edu/bfiero/tucsonecology/ adaptations/adaptations_home.htm Missouri Botanical Garden plant adaptations for various environments: http://www.mbgnet.net/ bioplants/adapt.html For desert animals from Desert USA: http://www. desertusa.com/survive.html Saguaro National Park Nature and Science Home Page: http://www.nps.gov/sagu/naturescience/ index.htm The National Park Foundation is the national charitable partner of the National Park Service. Extension activities: Pick any species group plant or animal that thrives in your local environment and challenge the students to list special adaptations they have for your environment. 5