Lab: Energy in a Cell and Cycling of Matter This assignment has two subparts. First, you will complete a virtual lab on photosynthesis and cellular respiration, and then you will conduct a lab to demonstrate how photosynthesis connects the carbon and oxygen cycles. After you have completed this assignment, please submit your work to the appropriate dropbox. Part I: Energy in a Cell Virtual Lab You will review and order the processes that make up photosynthesis and cellular respiration. Use the photosynthesis and cellular respiration guide to help you remember the steps in each process. Begin by going to the Energy in a Cell Virtual Lab as provided in the sidebar. Order the nine tiles in the correct manner based on the reactants and products of photosynthesis and cellular respiration. Once your sequence is correct, record the correct order in your notebook. Next, go to the journal (as indicated by the red arrow above) and answer the six essay questions provided. Record the correct energy sequence, and journal questions and answers for the analysis portion of your lab report. Part II: Cycles of Matter Begin this part of your lab by gathering the necessary materials and reading over the directions provided below. Consider what you have learned about photosynthesis and cellular respiration and correlate this information with your prior knowledge to prepare a thorough background, purpose, and hypothesis statement. Use your understanding of scientific methodology to address the purpose of the experiment and prepare a thorough and appropriate hypothesis. Materials & Procedure: baking soda 2 plastic syringes hole punch timer permanent marker metric ruler liquid dish soap baby spinach leaves clear plastic cups light source (100w bulb) plastic dropper USE CAUTION WHENEVER DOING EXPERIMENTS AT HOME. NEVER DO ANY EXPERIMENT WITHOUT ADULT SUPERVISION. WEAR SAFETY GLASSES WHENEVER WORKING WITH CHEMICALS OR GLASSWARE. This lab requires you to prepare several solutions for your investigations. Directions for making the solutions are found at the end of the lab. Photosynthesis is the primary driving force for almost all ecosystems present on Earth. This process unites the oxygen and carbon cycles and the rate of photosynthesis can be measured by the production of oxygen or the consumption of carbon dioxide. Why? Take a minute to think of the photosynthesis equation and consider how that is possible. 2H2O + CO2 + light à carbohydrate (CH2O) + O2 + H2O For this lab, you will use a floating disk technique to measure the rate of photosynthesis. Although it takes a little practice to master this technique, it is actually quite fun and effective. Inside plant leaves are tiny oxygen bubbles present (Where did they come from?) which causes the leaves to float when immersed in water. However, if you create a vacuum using a syringe to draw the oxygen out of the tiny spaces in the leaves, the leaves will sink instead. But the leaves won’t sink for long… The oxygen bubbles come back (why?) and the leaves begin to float again. •
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Prepare 300mL of bicarbonate solution (see directions below). This solution will serve as a source of carbon dioxide for the leaf disks while they are in solution. Pour the bicarbonate solution into a clear plastic cup to a depth of about 3cm. Label this cup “CO2”. Pour water into a second clear cup to a depth of about 3cm. Label this cup “control”. Using a pipette, add one drop of dilute liquid soap (see directions below) to each cup. The soap will act as a wetting agent necessary to allow the solutions to be drawn into the leaves. Using a hole punch, punch 20 uniform disks. Try to avoid the veins of the leaves and choose sections that are smooth and not too thick. Label one syringe “CO2” and the other “control”. Remove the plunger from both syringes and place 10 leaf disks into each syringe barrel. Carefully replace the plunger – do not crush the leaf disks. Push the plunger in until only a small volume of air remains in the barrel. Pull about 5cc of the CO2 plus soap solution into your “CO2” labeled syringe. Pull about 5cc of the control water plus soap solution into your “control” labeled syringe. Tap each syringe to suspend the leaf disks in the solution and push out the excess air, Now you will create a vacuum in the plunger to draw the oxygen out of the leaf tissue. This is the most challenging step! Create the vacuum by holding a finger over the narrow syringe •
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opening while drawing back on the plunger. Hold this vacuum for about 10 seconds and swirl the leaf disks so they are suspended in the solution. Check out the video in the sidebar for assistance on how this should be done. Open each syringe by removing the plunger and pour the disks into their corresponding cups -­‐ syringe “CO2” should empty into the “CO2” cup and the “control” syringe should empty into the “control” cup. Place both cups under a light source and start the timer. At the end of each minute, swirl the solutions and record the number of floating disks. Continue collecting data until all of the disks in the “CO2” cup are floating. Data Collection Record the correct energy sequence from Part I and record the qualitative and quantitative data you collected from Part II. Organize the data collected and be sure to label your data tables appropriately. Don’t forget to include pictures in your lab report. Analysis & Discussion Record the journal questions and answers from Part I and organize the data collected from Part II to prepare graphs. Graph should be a scatter plot of time on the x-­‐axis and number of disks floating on the y-­‐axis. You will need to use the graph to calculate the ET50. Conclusions Summarize your findings and analysis in complete and coherent paragraphs. Be sure to include the purpose of your experiment and relate your findings to your hypothesis. Also discuss limitations, possible sources of error, and means of improvement for your investigation. References Include all references in APA format. Don’t forget that you should have in-­‐text citations to correlate to the references included in this section. Solutions: • 1 M NaHCO3 solution: Add ½teaspoon of baking soda to 100ml of water. Stir to dissolve and add water to bring to 300ml total volume. • Soap solution: Add 2ml of liquid dish soap to water; bring to 100mL total volume Familiarize yourself with the lab report rubric on the next page. This is the rubric that will be used to grade this assignment and throughout the course, so be sure to review it carefully.
AP Environmental Science Lab Report Rubric When you complete your lab reports for this course, you will need to follow the guidelines included in the rubric below. Be sure to label each section of your lab report accordingly. Points Possible Title Prepare a specific and appropriate title that briefly describes the scope and purpose of your investigation. Introduction Develop 1-­‐2 informative paragraphs that describe the initial observations; problem statement; background information including important terms and key points related to the investigation; the purpose of the investigation and how it relates to the topic of study; and a testable hypothesis written in an if/then/because or null/alternative format. Materials & Procedures Compile a complete listing of the materials and supplies used with the exact steps followed to conduct the investigation. The narrative should include enough detail in the experimental design so that others can duplicate the investigation. Be sure to identify the control, variables, and the measurement techniques used. Data Collection Record all qualitative and quantitative data collected during the investigation. Data should include raw data, field notes, pictures, or drawings presented in appropriately labeled data tables or diagrams. Analysis & Discussion Summarize results as an explanation of the data as presented in the appropriate graphs and charts. Graphs must include descriptive titles, axes labels, and a legend if necessary. All mathematical determinations should be figured with complete formulas and error analysis as necessary. Required questions and answers must be included. Show all calculations, including equations and computation. Conclusion Describe what your findings mean and relate them to conclusions you can draw from the data. Give valid explanation based on correct interpretation of results in relation to hypothesis. Where appropriate, compare results with accepted values. Evaluate procedure and results to discuss limitations, weaknesses, or sources of error. State realistic suggestions to improve the investigation and questions for further investigation. Formatting Paper is properly formatted following class guidelines for font, margin and page settings. All lab reports should include in-­‐text citations and references to acknowledge the sources used to support findings and explanations. Total Points Points Earned 5 15 10 20 25 15 10 100