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Photosynthesis and Transpiration for Grades 5-6
Using Scientific Method to Learn About Plants Materials: Blackboard and chalk and/or large sheets of paper and markers; sunflower sprouts (sunflower seeds, clear plastic cups, paper towels); one or more potted plants (sweet potato vines, geraniums, ivy and philodendrons work well); small plastic bags, tape or twist ties, magnifying glasses. Background: Photosynthesis is a chemical process powered by energy from the sun. It transforms carbon dioxide and water into oxygen and sugar. On Photosynthesis In the transpiration cycle, plants move water from soil through roots and stems to leaves, where it evaporates into surrounding air. On Transpiration Groups: Divide class into groups of five or six—or work all together, taking turns to look at specimens Time: Three one-hour sessions (allow 48 hours between sessions for seedlings to sprout) Assignments: Short research report(s) on photosynthesis and/or plant respiration and/or osmosis and transpiration. Get Ready! Explain to students that you'll be growing and observing plants to learn about photosynthesis and transpiration. This lesson will give students a chance to talk about (1) what they know about how plants produce and consume nutrients, rely on sunlight for energy, and transform carbon dioxide to oxygen, (2) what they want to find out, and (3) how they can find answers to questions through scientific investigation. Start two lists on the blackboard: What We Know and What We Want To Know. Ask students to look up definitions of photosynthesis and transpiration. Step 1: Find Out What You Know Ask one or more students to begin the discussion by paraphrasing the definitions they've found. Give students a few minutes to think about what they know about what plants do. Do they eat? Do they breathe? How do they grow? Ask questions and brainstorm together to fill in the What We Know list. Questions may include • Do plants breathe? • What do plants eat? • How do plants drink? • Where do they get it from? • How do they get it inside themselves? • How do they "digest" it? • What does it become? You may prefer to have students work in small groups and list What We Know on large sheets of paper. When list(s) are complete, ask students to group responses into categories—for example roots and soil, stems and water, leaves and light. Step 2: Find Out What You Want to Know Based on what you know, make lists of questions you want to explore. Do your questions lead to more questions? • How does water get from the soil into the root? • How does air get into the plant? • How do all the ingredients in soil and water get transformed into plant tissue? • How do plants convert light, air, water, and the elements in soil into food that humans and other animals can eat? • What does "how a plant looks" have to do with "how it eats and grows"? Next, ask students if they can imagine ways to learn more about how and what plants consume. What kinds of experiments would they conduct? Allow students plenty of rein—let them design complex and crazy experiments. Then ask them to boil it down to a few questions. How does photosynthesis work? What are the basic requirements for photosynthesis? How can we really know that plants transpire? Give them some guidance in coming up with questions they can answer through experiment and research. To begin your investigation, give a short lecture or let students do some research themselves. Send them to the encyclopedia, the library, or on-line and ask them to write short reports of a paragraph or two on the basic processes. Step 3: Make Predictions and Conduct Experiments Students may come up with ideas for simple, doable experiments during brainstorming sessions. Or, you may suggest or guide them to the two below. Students should begin experiments as they are researching their short reports. Photosynthesis Experiment: What do plants need for photosynthesis? Transpiration Experiment: Can we demonstrate that transpiration is occurring? Step 4: Report and Reconsider When you have conducted experiments and compiled data, assess your results and draw conclusions. Were your predictions correct? Reconsider your original questions. What have your learned? Did you notice anything about how you were learning? Did everyone get the same results from their experiments? Is it important to test things more than once? Why? In-class assignment: Ask students to report the results of their experiments. If different students or groups of students did the same experiment(s) and got different results, ask them to compare and discuss. Who's right? What is the scientific way to answer this question? Suggest that interested students may conduct experiments a second time. |
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