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Photosynthesis and Transpiration What do sunflower sprouts need for photosynthesis? Materials: Sunflower seeds, clear plastic cups, paper towels Easy Instructions: Cut a paper towel in half; fold one piece in half and use it to line a plastic cup. Wad up the other half and stuff it into the cup to hold the liner in place. With your fingers, slide a sunflower seed between the paper liner and the side of the cup. Seed should be no more than an inch from the top of the cup. You can put as many as four seeds in one cup. You can also try a couple more in the folds of the wadded towel. Put a little water into the cup, making sure that the water level is below the seeds. The paper liner will wick moisture up to the seed. Start lots of sprouts for everyone. Make sure to reserve some for controls. As soon as roots appear, place sprouts where they'll get a little direct sunlight every day until well established. It should take only a day or two for a small root to appear at the end of each seed—a few more days for a stem and two tiny leaves or cotyledons to appear at the other end. Begin experiment with a class discussion about the things seeds may need to sprout and what plants need to photosynthesize. Make a list of minimum requirements and another that describes optimum conditions. Ask students how they know what seeds need. Have they planted gardens or studied germination? Is it true that a healthy green plant is probably photosynthesizing? How can you tell? (Is it GROWING?) Have students conducted other experiments? What is the difference between an experience and an experiment? (Look these words up in the dictionary and discuss their definitions.) Describe the importance of a control. Have students work in small groups to design experiments testing 1. The hypothesis that seedlings need—sunlight, air, warmth, water, soil, etc.—for photosynthesis. 2. The hypothesis that seedlings will be more likely to photosynthesize if they're grown as described by the optimum conditions list. Ask students to write simple hypotheses, general descriptions of experiments to test hypotheses and predictions. For example: Sprouts need water for photosynthesis; deprive a sprout of water; sprout will wilt and die—will it lose it's chlorophyll before it dies? Will it be possible to revive it after it's wilted and turned yellow? Have students choose what they think are the most promising of their experiments and conduct them, carefully recording their procedures and results. What will they use as a control? Should they allow some seeds to sprout and grow in the conditions they described as optimum? Should different students conduct the same experiments and compare results? Why? What standards will they use to judge whether a sprout is doing well? Suggest that they consider the time it takes to germinate, rate of growth once stems to appear, color, overall size, and hardiness. Ask how they will measure these. Will they make comparisons? Why? In-class Assignment: Ask students to write reports of their hypotheses, predictions, procedures, and standards. Review these before experiments begin. Encourage students to be creative and to try as many things as they can think of—see easy experiments with sunflower sprouts. At the same time, encourage them to observe closely and make careful, complete notes. Notes should include drawings. Remind students that they are doing exactly what scientists do. Suggest that their observations and notes should meet the standards of carefulness and completeness they would expect from other scientists. In-class Assignment: Ask students to hand in their notes for your review. Discuss ways to analyze results. For example, what exactly can you conclude if a sprout in a dark closet turns yellow and dies? Are there factors other than darkness that may have affected photosynthesis—cold, lack of circulating air, lack of soil, mold? Is this one sprout a fair representative of all sunflower sprouts or of all kinds of plants? What can you do to make an experiment as informative as possible—would it have been smart to put more sprouts in the closet or another kind of sprout? Did students' experiments answer their original questions? If not, why not? In-class Assignment: Ask students to think of ways to display their results. Can they compare seedling growth on bar charts or line graphs? Suggest that students work together, combining data, to create more interesting comparisons. |
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