12E Describe the flow of matter through the carbon and nitrogen cycles and explain the consequences of disrupting these cycles. 12F Describe how environmental change can impact ecosystem stability. 2E Plan and implement descriptive, comparative, and experimental investigations, including asking questions, formulating testable hypotheses, and selecting equipment and technology. Lab 12E, 12F, 2E: Acid Rain and Seeds Introduction Every seed contains a tiny living plant and a food supply to nourish it when the plant first begins to develop. The plant and the food supply are enclosed in a protective coat, which keeps the contents of the seed from drying out. The tiny plant can survive for weeks, months, or even years. Factors such as temperature and moisture determine when the plant within the seed will start to grow again. This resumption of growth is called germination. Before seeds can germinate, they must absorb water, which causes the food-storing tissues to swell and crack the seed coat. The root is the first part of the plant to emerge from the seed. In the atmosphere, pollutants react with water vapor in the air. Eventually this falls back to Earth as acid rain or other forms of precipitation. All rain is mildly acidic because carbon dioxide forms a weak acid when it dissolves in water vapor. If the ph of rain falls below 5.0, the rain is usually classified as acid rain. In this lab, you will design an experiment to determine whether the ph of the water that a seed absorbs can affect germination. Materials 5 large test tubes test-tube rack glass-marking pencil 25-mL graduated cylinder 5 solutions of vinegar and water ph paper 120 dried beans paper towels zip-close plastic bags stick-on labels hand lens graph paper 1
Safety Wear goggles and a lab apron when you handle the solutions. Rinse off any solution that spills on your skin or clothing. If you use glass test tubes or graduated cylinders, check for cracks or chips. Alert your teacher if you break a glass object. Wash your hands thoroughly with soap and warm water before leaving the lab. Pre-Lab Questions 1. Compare and Contrast How similar are the solutions you will use in this experiment? How are they different? Explain. 2. Use Models What do the solutions represent? 3. Infer How will you know that a seed has germinated? Procedure Your teacher has prepared 5 solutions of vinegar and water, which are labeled A E. Each solution in the series is 8 times as dilute as the previous solution. Solution A is the most concentrated. Solution B is 8 times as dilute as Solution A, Solution C is 8 times as dilute as Solution B, and so on. Part A: Measure the ph of the Solutions 1. Put on your safety goggles and apron. 2. Place 5 large test tubes in a rack. Label the test tubes A, B, C, D, and E. 2
3. Use the graduated cylinder to place 15 ml of Solution A in the test tube labeled A. Rinse out the cylinder. 4. Repeat Step 3 for each of the other solutions. Be sure to place each solution in the correct test tube. 5. Select Equipment and Technology With your teacher s guidance, select the proper equipment or piece of technology to measure the ph of each solution. Record the results in Data Table 1. Solution A Data Table 1: ph of Solutions Dilution Compared to Solution A none ph B 8 C 64 D 512 E 4096 3
Part B: Design Your Investigation 6. Formulate a Testable Hypothesis How will changing the ph of a water-based solution affect the percentage of seeds that germinate? Record your hypothesis below. Hypothesis: 7. Control Variables What will your independent variable be? What will your dependent variable be? Independent Variable: Dependent Variable: 8. Plan and Implement Your Investigation Record the details of your plan. You will have 120 dried beans and 5 solutions to work with. Which variables will you need to control? Before you begin, have your teacher review your plan. Plan: 4
9. Collect and Organize Quantitative Data Construct a data table in the space below. You will need columns for the ph values of the solutions being tested and for the number of seeds that germinate. You might want to include a third column for other observations. 10. Disposal After you gather your data, follow your teacher s instructions for cleanup and for the disposal of materials. Then wash your hands thoroughly with soap and warm water. 5
Analyze and Conclude 1. Calculate Use your data to calculate the percentage of seeds that germinated at each ph. Record the results in Data Table 3. Data Table 3 ph of Solution Percentage of Seeds Germinated 2. Graph Use the results from Data Table 3 to make a graph. Plot the ph on the x-axis and the percentage of seeds germinated on the y-axis. 6
3. Interpret Graphs Does the graph support the hypothesis you made in Part B of the procedure? Why or why not? 4. Infer At the time that bean plants and other seed plants evolved, what do you think the ph of the rainfall was? Explain. 5. Evaluate Models Identify at least one way that this lab was not a perfect model for the effect of acid rain on the germination of seeds. 6. Relate Cause and Effect Explain why acid rain could harm animals as well as plants. Which types of animals do you think would be most at risk from acid rain? 7
7. Explain Explain how acid rain and its effects on seed germination might or might not be a consequence of disrupting the nitrogen cycle. 8. Describe Describe how environmental change (such as acid rain) could impact ecosystem stability. 8