BUILT FOR THE DESERT · BACKGROUND Stems – hold up the plant so it can Students identify reach for the sunlight saguaro adaptations Saguaro cacti, like other plants, have an · Flowers – attract pollinators to help for desert life and assortment of general parts that help them produce fruits and seeds transform an average to survive and reproduce. Saguaros with · Fruits – attract animals to eat them potted plant into a their many structural modifications are well- and spread the seeds they contain desert-adapted adapted to the Sonoran Desert. The stem · Roots – take in water and dissolved saguaro. and arms are succulent, comprised of minerals for the plant spongy tissue for water storage. A woody skeleton of vertical ribs runs through them, 2) Ask the students if they would expect providing structural support. The outer skin to see a plant like this growing in the of the saguaro is waxy to prevent water desert? Why or why not? (Those who loss through evaporation. It also contains have been out in the desert will realize chlorophyll and is the site of photosynthesis that plants like the potted plant are – by eliminating leaves, cacti are able to pretty unusual there. They may com- reduce water loss even further. Saguaros ment that it is too green and leafy, or are covered with rows of spines that serve that it needs too much water to live to help protect the cactus from predation well.) by food- or moisture-seeking animals, as 3) Ask, “What about the desert makes it well as to protect its sensitive growing tip challenging for plants to grow?” (It is from extreme heat or cold. Saguaros have hot and dry, with a high rate of evapo- shallow, extensive roots that absorb rainfall ration.) Have the students think back to near the surface of the ground. As the what they learned in the Saguaro Tales cactus takes in water, the stem and arms Discovery Class. What do saguaros are able to expand along a series of have that help them face these chal- accordion-like pleats. During dry periods, lenges and live well in the desert? the cactus shrinks again as the cactus (Saguaros have many of the parts that ARIZONA SCIENCE gradually uses its stored water. other plants do, but theirs have special STANDARDS features or adaptations that help them SC03-S4C4-01 GETTING READY survive in the desert.) Prepare the materials as listed in the margin of the next page. OBJECTIVES COMPARING PARTS Students should: · Identify adaptations DOING THE ACTIVITY 1)Provide a copy of Student Handout - of the saguaro that Built for the Desert, scissors, mark- allow it to live in the SETTING THE STAGE ers/crayons, and glue for each student. Have the students cut out the picture of desert. 1) Show the students the potted plant. . the leafy plant and paste it in the middle Point out the leaves, stems, and flowers, of the construction paper. Ask, “How and ask them to identify these parts. can we change this leafy plant into a Unearth a bit of the plant and show them saguaro?” the roots. As you look at the different 2) Have the students cut out the saguaro parts, ask the students to explain the parts along the dotted lines and lay purpose of each. Reiterate these func- them on the table. Point out the leaves, tions as you demonstrate the parts: stems, and roots of the leafy plant and · Leaves – food factories for the plant discuss how each corresponding part is (make food with sunlight, water, and modified and adapted for desert life on air) Teacher Information Desert Discovery Class © 2000, revised 2008 ASDM BUILT FOR THE DESERT

the saguaro (as outlined in steps A-D and widespread instead of deep and below.) As you discuss each part, the narrow.) “Why?” (The rains that fall students can overlay and glue the on the desert are often quick and saguaro parts over the leafy plant parts their water does not soak deeply on the construction paper. into the soil. The saguaro has shal- A. Begin with the leaves. Ask, “What low, widespread roots to absorb the are the leaves for on the plant?” rainwater before it evaporates or (They are where the plant makes its runs off.) Paste the saguaro root food.) “What happened to the leaves overlay over the leafy plant’s roots. on the saguaro?” (It got rid of leaves With a marker, draw the extension of to save water. Leaves have many tiny the roots to the edges of the con- holes that lose much water to evapo- struction paper. ration. The saguaro stem, in contrast, has few holes and is covered with a waxy coating to help keep water DISCUSSION inside.) “How does the saguaro make 1) Ask the children to compare the its food now?” (With its stem.) Have saguaro and the leafy plant. Ask, “How the students color the saguaro stem are saguaros and the leafy plant the MATERIALS green, then overlay the image onto same?” (They both have stems, they are · Chalkboard the plant leaves and stem. both green, and they both have roots.) · A potted non-desert B. Ask, “What else does the stem of the “How are they different?” (The saguaro plant with leaves, saguaro do?” (It stores water.) “How is spiny, it has no leaves, and it stores stems, and flowers does it do this?” (It has pleats that water in its stem, while the leafy, potted (like marigolds, tulips, expand and let it take up lots of plant does not.) or geraniums) water, then shrink back down as it 2) Ask, “How do these differences help · A copy of Student uses the water.) Have the students the saguaro cactus live in the desert?” Handout - Built for cut the yarn into pieces about the (They can store water in their stems and the Desert for each height of the saguaro cactus and glue live without frequent rainfall, they can student them vertically along its stem to protect the stored water with their · A piece of con- represent pleats. spines, and they can help prevent struction paper for C. Ask, “What things might be a threat evaporation of the water by having no each student to all that water stored inside the leaves and having a tough, waxy skin.) · Markers or crayons saguaro?” (Animals looking for 3) Reiterate that these are adaptations of · A piece of black or water.) “How does the saguaro the saguaro that help it survive the high brown yarn (about 2’ protect these?” (It is covered with heat, low water, and high evaporation long) for each student spines to keep animals away. The of the desert. · Scissors spines also block the sun’s rays from · Glue directly hitting the cactus. And the water is stored in the stem in a toxic EXTENSION form.) Have the students draw spines VOCABULARY around the edges of the cutout Have the students illustrate and write/ Adapt saguaro stem. dictate a story from the point of view of a Adaptation D. Ask, “What are the leafy plant’s roots saguaro. Have them explain how the Pollination for?” (taking in water and dissolved saguaro survives in the desert. What Pollinator minerals) “How are the saguaro’s adaptations does it have? How does it get Spines roots different?” (They are shallow and store water? What are some of the animals that visit it?

Teacher Information Desert Discovery Class © 2000, revised 2008 ASDM