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Sprout & Dissect Onions for Grades K-3
Materials: Three small onions, yellow or white, purchased from a natural foods store or farmers' market; one lemon, sliced; 2 cups (paper or plastic), clean gravel, plastic knife Easy Instructions: Fill cups with gravel to within an inch of the top. Place onions on gravel, pointed end up. Fill cups with water to base of onions. Set cups in a sunny window or where they'll get plenty of diffused light. Cut open third onion so that students can see what's inside. Use your lemon slices to clean hands at the end of this activity. Suggestion: It is important to get your onions from a natural source, to insure that they haven't been treated to prevent sprouting. Regular supermarket onions will take much longer to develop roots and may mold before they sprout. This activity allows students to see what happens inside a bulb as it grows. Begin by ASKING questions. What do students expect to see within the first onion when you cut it open today? Where is the tiny baby plant hidden? Pass the onion around so that everyone can OBSERVE. IDENTIFY the disk-shaped stem at the base of the onion. You may see the remnants of little roots on the bottom of the stem. The onion's layers are fleshy leaf bases, in which food is stored. The dry, papery leaf bases on the outside protect the bulb from insects and germs. At the center of the onion is an apical bud—the part of the onion that contains immature leaves. This is the embryo (tiny baby plant) of the future sprouted onion. Pass leaves and the apical bud around so that everyone can touch and see. What will your potted onions do? What will appear first, the roots or the stem? Why? Sprouts need water. How will the onion get water from the pot? Will your onion produce a flower? (HINT: It's possible, but your onion is likely to exhaust its stored food long before a flower buds.) Try dissecting your second onion soon after the first shoot appears. What's different now? What are the sprouting onions eating? What's happening to the bulb? |
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