Floating Disks An Investigation of Photosynthesis

Transcription

1 Floating Disks An Investigation of Photosynthesis Teacher Materials In this laboratory, students measure the rate of photosynthesis under various light conditions using small disks cut from plant leaves and a vacuum syringe. This lab can be easily expanded to include student-centered investigations. * Learning Goals, Objectives, and Skills... 2 Instructor Planning Guide... 3 Instructor Preparation Guide... 5 Answers to Student Questions... 7 Post-Lab Extension Activities... 9 Additional Resources Practice MCAS & AP Questions Standards Alignments *Please consider adapting this lab to include some student-centered investigation. Some suggestions, ideas, and tips can be found in a separate document called "Student- Centered Investigation Last updated:

2 Student Learning Goals: Floating Disks Learning Goals Students will understand the basic process of photosynthesis. Students will understand the role of environmental factors in photosynthetic rate. Student Learning Objectives: Students will articulate the function of photosynthesis and identify the reactants and products of this reaction. Students will measure the effect of light and other factors on photosynthesis. Scientific Inquiry Skills: Students will pose questions and form hypotheses. Students will design and conduct scientific investigations. Students will make measurements and record data. Students will use mathematical operations to analyze and interpret data. Students will generate tables and graphs to present their data. Students will use experimental data to make conclusions about the initial question and to support or refute the stated hypothesis. Students will follow laboratory safety rules and regulations. Laboratory Technical Skills: Students will demonstrate proper use of micropipettors. 2

3 Floating Disks Instructor Planning Guide Experimental Timing: From start to finish this lab can be completed in a single 60-minute class period. However, this lab can also be spread over 2 days or 2 class periods. It is recommended that the pre-lab discussion and teacher demonstration of the procedure be completed the day before the lab. Specialized Equipment Needed for Lab: Fluorescent lights (15 watt) 10 ml syringes Ordering Information: This lab was developed with materials and reagents that can be found in most classroom or easily purchased from a grocery store. Procedure Tips: 1. Before starting the experiment, ask students to check their materials list to make sure they have everything. 2. Students will be working in groups of two, make sure both students actively participate in the lab. 3. Be sure to demonstrate for your students how to set up the experimental and control syringes and/or have them watch our short instructional video prior to beginning the lab. (Video link: ) Be sure to demonstrate the procedure for creating the vacuum in the syringe. It is important that students make a tight seal with their thumb while pulling back with the other hand. The vacuum should be held for five seconds and then released. When expelling the air from the syringe or releasing the vacuum, the students should be careful to avoid pointing the tip of the syringe at their peers sometimes the solution can squirt out. Students may have to repeat the vacuum procedure several times to get all the disks to sink. However, it is possible to overdo it, and damage the leaf tissue. If students have tried several times and the leaf disks are not sinking, suggest they get fresh disks. 4. If you are in an interior, windowless room, make sure that all the overhead lights are on to maximize the ambient light. Please note: Depending on the ambient light, the control disks may not float this is not unusual. 5. Syringes should be within 5-10 cm of the light for best results. 6. If you choose to use spinach leaves to conduct the experiment, be sure you purchase baby spinach as it works much better than mature leaves. 3

4 Teaching Tips: During the wait time, you could suggest one of the following to keep your students engaged: 1. Ask students to design a modified experiment to test other variables. 2. Choose from the suggested post-lab extension activities. 3. Give them a diagram of a non-plant eukaryotic cell and ask them to modify the diagram to make it a plant cell. Have them indicate where the processes of photosynthesis and cellular respiration occur. Safety Considerations: Gloves, lab coats and eye protection should be used whenever possible, as a part of good laboratory practice. Exercise caution when handling the lights as they may become hot and present a burn hazard. Always wash hands thoroughly after handling biological materials or reagents. Check with your school s lab safety coordinator about proper disposal of all reagents. 4

5 Floating Disks Instructor Preparation Guide Materials: This guide assumes 30 students, working in groups of two, for a total of 15 groups. Materials for Teacher Advanced Preparation: 2 g baking soda 1 ml dish detergent 500 ml tap water 1 bag of baby spinach leaves (16 oz.) or seedlings ml beakers or small cups ml flask or bottle 1 1 L graduated cylinder 1 balance Student Workstation: Common Workstation: 2-3 fresh young leaves or about 8 plant seedlings 5+ light sources 35 ml baking soda/detergent solution 2 sections of drinking straw (5 cm) ml beaker or small cup 1 50mL or 100 ml graduated cylinder ml beaker 3 10 ml syringes 1 piece of aluminum foil (10 cm 2 ) Easy substitutions: Fresh baby spinach leaves can be purchased from any grocery store. A 1-lb bag should be sufficient. As an alternative, students could grow young plants using radish seeds or Wisconsin Fast Plant seeds. Seeds should be planted 5 7 days before the day of the experiment. Plastic deli containers or cups can be substituted for beakers. Warm white LED lights can be substituted for 15-watt florescent bulbs. However, you may find that you need to move the syringes closer to the lights and that the disks may take slightly longer to rise than with the florescent bulbs. Set-up Calendar: 2 Weeks Before Lab: Check supplies and order any needed materials. If making any substitutions to the supply list, edit the student protocol accordingly. 1 Week Before Lab: (Optional) Plant radish or Wisconsin Fast Plant seeds. 5

6 2 3 Days Before Lab: Purchase fresh baby spinach leaves. 1 Day Before Lab: Set up student lab stations with all durable materials according to the materials listed above. Set up 5 or more lights at stations around the room. We recommend 15-watt spiral fluorescent bulbs. Morning of Lab: Immerse the spinach leaves in water and put the container under a bright light. Prepare baking soda/detergent solution o Add 2 grams baking soda to 500 ml tap water. Stir or shake until dissolved. o Add 3 drops detergent to the baking soda solution, gently stir, try not to create too many bubbles Aliquot 35 ml of baking soda/detergent solution into each of mL beakers or small cups (1 per student lab group). Tip: If you have multiple classes doing the experiment on a single day, aliquot enough baking soda/detergent solution for all the lab groups at a station for the day in a bottle. Students can measure out their own solution in step 1 of the protocol. Beginning of Class: Distribute 2 3 leaves OR 8 seedlings to each lab station. 6

7 Floating Disks Answers to Student Questions Protocol-Embedded: p. 2: Sample answer: You could measure the rate of photosynthesis by collecting released O 2 or by figuring out how much glucose the plant has produced. You could also measure how much CO 2 is used up. The leaf disks float initially because there are air spaces between the cells. The trapped air makes the leaf disks less dense than water. Pre-Lab: 1. The baking soda (NaHCO 3) is the source of carbon which the cells use to make glucose. 2. Experimental controls help to show that the results you get are caused by the variable you re testing not by the reagents. 3. The syringe in the dark and in ambient light serves as the control. 4. No, we expect the disks in each tube will behave differently. The leaf disks will photosynthesize more or less depending upon the light conditions. Under the bright light the disks can photosynthesize more and as a result produce more glucose and O 2. The disks in ambient light may have enough light to photosynthesize and if so they will also float, but it will take longer to produce enough O 2 for each disk to float. The disks in the dark will not float because photosynthesis requires energy from light. 5. Photosynthesis releases oxygen, which displaces the detergent solution in the intercellular spaces and makes the leaves less dense than water. Post-Lab and Analysis: 1. Expected answer: The tube under the bright light had the most floating disks. This matches my pre-lab prediction. 2. The higher the light intensity, the more energy available for the reactions of photosynthesis, so the faster the rate of photosynthesis. More photosynthesis produces more glucose and O 2. The air is trapped between the cells and makes the leaf disks less dense than water. Our data shows that the disks under bright light floated faster than those under ambient light, and the disks in the dark did not float at all. 3. Sample answer: I d expect that none of the disks would float in any of the tubes. Photosynthesis requires enzymes, and enzymes will denature if they are boiled. 7

8 Sample data table: Time (minutes) Number of Leaf Disks Floating Bright light Ambient light No light

9 Student Oral Presentation: Floating Disks Post-Lab Extension Activities Students can report the findings of their student-centered investigations to the class using a PowerPoint presentation that includes the following information: Experimental question what you hope to learn from performing the experiment. Hypothesis a testable, proposed answer to the experimental question based on prior knowledge. Experimental system and data collection methods flowchart of how the experiment was performed and how data was collected. This should NOT include a detailed summary. Results observations, data tables, figures, etc. Conclusions should the hypothesis be accepted or rejected as supported by key data. Online resource for effective PowerPoint presentations: Student Lab Report: Students can report the findings of their student-centered investigations through a written lab report. Your school may have its own lab report format, but generally lab reports include the following information: Title brief summary reflecting the factual content of the investigation. Introduction includes questions being answered, hypothesis and background information. Materials list of supplies needed to perform the lab. Procedure step-by-step procedure (with enough detail so someone could repeat the experiment). Results observations, data tables, figures, etc. and a brief narrative summary of results. Conclusion explanation supported by evidence for whether the hypothesis should be accepted or rejected. Online resources for writing lab reports: Student Writing Exercise: Ask students to read a current newspaper or journal article related to biofuels and write a paragraph answering a series of prompts. For example, students could read the online article, How plants can suck water from the sky ( ) and write a response to the following statement: The discovery that some plants can collect water from the atmosphere will revolutionize agriculture. 9

10 How plants can suck water from the sky How does water travel through a plant? Your answer's probably a simple one. Water moves from the soil, up through the roots and stems of a plant, through the leaves and out into the surrounding atmosphere. But recent research has shown that our traditional understanding of the movement of water through plants is incomplete. Under certain specialized conditions, some plants have evolved the ability to absorb water through their leaves, move the water down the xylem, and then it can release the water into the soil. The plants are actually watering their own roots - and their own seedlings. This off-beat mechanism for water uptake works well enough that these plants can continue to photosynthesize and grow, even when the soil they are growing in are dry. The trees the researchers studied - Drimys brasiliensis - grow in the cloud forests of Brazil, where the trees are almost constantly covered in fog. The atmosphere around the leaves has a higher water potential than the leaves themselves, allowing foliar water uptake. The exact pathway for water entry is still under discussion: this particular species has a hydrophilic cuticle that could facilitate water entry, as well as hydrophilic tissues within the leaf that could provide water storage. At least 70 species, across seven different ecosystems, have been identified as using this 'back-to-front' water transport mechanism, pulling water out of the sky and down to the rhizosphere. These new findings have important implications for our existing models of the climate and our ecosystems, which often consider soil water as the only source of water for plants. It's another example of how plants are constantly over-turning our expectations. Source: Science & Plants for Schools, Biology News. Accessed 12 August Eller, C. B., Lima, A. L. and Oliveira, R. S. (2013), Foliar uptake of fog water and transport belowground alleviates drought effects in the cloud forest tree species, Drimys brasiliensis (Winteraceae). New Phytologist, 199: doi: /nph

11 Floating Disks Additional Resources Websites: Videos: Games: %2F%2Foutreach.mcb.harvard.edu%2Fteachers%2FSummer09%2FEdBarry%2FPhotosynthesisGame.ppt &ei=9jhqu8awfi78yqtd8ocobg&usg=afqjcnfjhlxefw8x9yvvlwmhcraj9cwmfq&sig2=3ito6gdlpdi1yz WAcZaDQA Related Experiments:

12 Practice MCAS Questions: Floating Disks Practice MCAS and AP Questions The following multiple-choice questions from the spring 2013 and spring 2010 Biology MCAS test probe student understanding of the interconnectedness of photosynthesis and cellular respiration. Which of the following statements describes a difference between photosynthesis and cellular respiration in plants? A. Photosynthesis occurs only during the day, whereas cellular respiration occurs only at night. B. Photosynthesis involves only one reaction, whereas cellular respiration involves many steps. C. Photosynthesis occurs only in cells containing chlorophyll, but cellular respiration occurs in all cells. D. Photosynthesis converts light energy into chemical energy, but cellular respiration converts light energy into heat energy. Which of the following statements correctly describes the processes of photosynthesis and cellular respiration? A. Photosynthesis and cellular respiration occur in the same organelle. B. Photosynthesis and cellular respiration are performed by all organisms. C. Photosynthesis produces carbon dioxide, and cellular respiration uses carbon dioxide. D. Photosynthesis stores energy for cells, and cellular respiration releases energy for cells. The following open-response question from the spring 2012 Chemistry MCAS test probes student understanding of photosynthesis. Sample student responses can be found at: BE SURE TO ANSWER AND LABEL ALL PARTS OF THE QUESTION. Show all your work (diagrams, tables, or computations) in your Student Answer Booklet. If you do the work in your head, explain in writing how you did the work. Glucose (C 6H 12O 6) is formed in plants by the process of photosynthesis. The net equation for photosynthesis is shown below. sunlight 6CO 2 + 6H C 6H 12O 6 + 6O 2 a. Calculate the molar mass of glucose. Show your calculations and include units in your answer. b. Explain how the amount of carbon dioxide consumed by a plant can be determined from measuring the amount of oxygen released by the plant. Assume excess water is available. c. Calculate the amount of glucose, in grams, formed when 100 mol of O 2 is released. Show your calculations and include units in your answer. 12

13 Practice AP Exam Questions: The following multiple-choice questions were pulled from the fall 2012 AP Biology Course and Exam Description booklet. A student placed 20 tobacco seeds of the same species on moist paper towels in each of two petri dishes. Dish A was wrapped completely in an opaque cover to exclude all light. Dish B was not wrapped. The dishes were placed equidistant from a light source set to a cycle of 14 hours of light and 10 hours of dark. All other conditions were the same for both dishes. The dishes were examined after 7 days, and the opaque cover was permanently removed from dish A. Both dishes were returned to the light and examined again at 14 days. The following data were obtained. Dish A Dish B Day 7 Covered Day 14 Uncovered Day 7 Uncovered Day 14 Uncovered Germinated seeds Green-leaved seedlings Yellow-leaved seedlings Mean stem length below first set of leaves 8 mm 9 mm 3 mm 3 mm According to the results of this experiment, germination of tobacco seeds during the first week is (A) increased by exposure to light (B) unaffected by light intensity (C) prevented by paper towels (D) accelerated in green-leaved seedlings Additional observations were made on day 21, and no yellow-leaved seedlings were found alive in either dish. This is most likely because (A) yellow-leaved seedlings were unable to absorb water from the paper towels (B) taller green-leaved seedlings blocked the light and prevented photosynthesis (C) yellow-leaved seedlings were unable to convert light energy to chemical energy (D) a higher rate of respiration in yellow-leaved seedlings depleted their stored nutrients 13

14 Floating Disks Standards Alignments MA Science and Technology/Engineering Standards High School (2016) Biology HS-LS1-5. Use a model to illustrate how photosynthesis uses light energy to transform water and carbon dioxide into oxygen and chemical energy stored in the bonds of sugars and other carbohydrates. HS-LS2-4. Use a mathematical model to describe the transfer of energy from one trophic level to another. Explain how the inefficiency of energy transfer between trophic levels affects the relative number of organisms that can be supported at each trophic level and necessitates a constant input of energy from sunlight or inorganic compounds from the environment. HS-LS2-5. Use a model that illustrates the roles of photosynthesis, cellular respiration, decomposition, and combustion to explain the cycling of carbon in its various forms among the biosphere, atmosphere, hydrosphere, and geosphere. Chemistry HS-PS1-5. Construct an explanation based on kinetic molecular theory for why varying conditions influence the rate of a chemical reaction or a dissolving process. Design and test ways to slow down or accelerate rates of processes (chemical reactions or dissolving) by altering various conditions. * NRC Practices Asking questions and defining problems Planning and carrying out investigations Analyzing data Mathematical and computational thinking Constructing explanations and designing solutions Engaging in argument from evidence Obtaining, evaluating and communicating information Next Generation Science Standards High School (2013) Life Sciences HS-LS1-5. Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy. HS-LS2-5. Develop a model to illustrate the role of photosynthesis and cellular respiration in the cycling of carbon among the biosphere, atmosphere, hydrosphere, and geosphere. 14

15 Physical Sciences HS-PS1-5. Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs. Common Core State Standards Connections: ELA/Literacy RST RST RST RST RST RST WHST WHST WHST WHST WHST SL Translate quantitative or technical information expressed in words in a text into visual form (e.g., a table or chart) and translate information expressed visually or mathematically (e.g., in an equation) into words. Assess the extent to which the reasoning and evidence in a text support the author s claim or a recommendation for solving a scientific or technical problem. Cite specific textual evidence to support analysis of science and technical texts, attending to important distinctions the author makes and to any gaps or inconsistencies in the account. Integrate and evaluate multiple sources of information presented in diverse formats and media (e.g., quantitative data, video, multimedia) in order to address a question or solve a problem. Evaluate the hypotheses, data, analysis and conclusions in a science or technical text, verifying the data when possible and corroborating or challenging conclusions with other sources of information. Synthesize information from a range of sources (e.g., texts, experiments, simulations) into a coherent understanding of a process, phenomenon, or concept, resolving conflicting information when possible. Write arguments focused on discipline-specific content. Write informative/explanatory texts, including the narration of historical events, scientific procedures/ experiments, or technical processes. Develop and strengthen writing as needed by planning, revising, editing, rewriting, or trying a new approach, focusing on addressing what is most significant for a specific purpose and audience. Conduct short as well as more sustained research projects to answer a question (including a self-generated question) or solve a problem; narrow or broaden the inquiry when appropriate; synthesize multiple sources on the subject, demonstrating understanding of the subject under investigation. Draw evidence from informational texts to support analysis, reflection, and research. Make strategic use of digital media (e.g., textual, graphical, audio, visual, and interactive elements) in presentations to enhance understanding of findings, reasoning, and evidence and to add interest. 15

16 Mathematics MP.2 MP.4 HSF-BF.A.1 HSF-IF.C.7 HSN.Q.A.1 HSN.Q.A.2 HSN.Q.A.3 HSS-IC.A.1 HSS-IC.B.6 Reason abstractly and quantitatively. Model with mathematics. Write a function that describes a relationship between two quantities. Graph functions expressed symbolically and show key features of the graph, by hand in simple cases and using technology for more complicated cases. Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays. Define appropriate quantities for the purpose of descriptive modeling. Choose a level of accuracy appropriate to limitations on measurement when reporting quantities. Understand statistics as a process for making inferences about population parameters based on a random sample from that population. Evaluate reports based on data. 16