HASPI Medical Biology Lab 06 Background/Introduction The Purpose of Photosynthesis Photosynthesis is a process that takes light energy and converts it into chemical energy. Why this is important: Because LIFE on Earth would not be possible without this process! Our bodies need energy to perform even the simplest functions, like breathing, but we are unable to use light energy from the sun as an energy source. Photoautotrophs, including plants, algae, and some bacteria, are organisms capable of performing photosynthesis, and thus they convert/provide energy for us. Energy Transformations http://www.dstudy.org/wp-content/uploads/03/0/0303_33_conservatio.jpg It is important to remember that energy cannot be created or destroyed. As light energy is absorbed by a photoautotroph, some of the energy is converted and saved in a chemical form. It remains in this form until it is released. For example, when we consume broccoli that has stored light energy in molecules, we are able to break down those molecules in the process of digestion, which releases the energy. Our bodies are able to use this chemical energy to perform basic functions. The energy does not disappear when we use it, but instead it changes form again to be released from our bodies as heat. The Process of Photosynthesis Photosynthesis is actually a series of chemical reactions. There are three components needed for a photoautotroph to perform photosynthesis: Carbon dioxide, water, and light. These items come together and are rearranged by the photoautotroph to produce a sugar, called glucose, and oxygen. The following equation summarizes the reactants (what goes into the reaction) and the products (what comes out of a reaction) of photosynthesis: Reactants Products 6 CO + 6 HO light 6 O + C6HO6 carbon dioxide water oxygen glucose Notice from this equation that the same amount of reactants are found in the products. For example, there are 6 total carbon dioxide molecules, which means there are 6 carbon atoms going into the reaction. These 6 carbons can be found in the glucose molecule as a product. The same can be seen for oxygen and hydrogen. Light energy is needed to make this reaction occur and to create the bonds between the carbon, hydrogen, and oxygen of glucose. In this way, the light energy is held in the bonds holding glucose together. When plants, or organisms that consume plants, break the bonds in glucose, they release (and are able to use) the energy. Why is it that only photoautotrophs can perform photosynthesis? They contain specialized proteins that contain chlorophyll, a pigment capable of absorbing the energy in light. These proteins are found in an organelle called the chloroplast. The energy absorbed by 05
chlorophyll is used to drive the chemical reaction that creates and stores that energy in glucose. Oxygen is actually just a by-product of photosynthesis and is released by the photoautotroph into the atmosphere. Photosynthesis and Medicine Hopefully it has been made clear how important photosynthesis is for life, but the process itself has medical application. Most obviously, there are many plants that have medicinal properties. Mint has been reported to calm the stomach, soothe headaches, and fight nausea. Aloe vera can aid in wound healing, treat burns, and improve circulation. Sage is reported to be anti-inflammatory, anti-fungal, and can relieve digestive distress. These are only a few examples of how plants can improve our health. In addition to these obvious medical connections of plants, photosynthesis can also be used to synthesize medications and exists in a new treatment called photodynamic therapy. Photosynthesis to Produce Medications Through recent research, it has been discovered that it is possible to re-engineer the photosynthetic process to produce more than just glucose. In the future, plant cells may be used to manufacture drug components for medications, fabrics, and even fuels using photosynthesis. In this process, light energy would be transferred into the bonds to create these products. Photodynamic Therapy Photodynamic therapy is a treatment that uses a specific wavelength of light to destroy cancer cells. A drug called a photosensitizer is injected into a patient s bloodstream. The photosensitizer would normally be eliminated from the body by the kidneys in -7 hours, but remains in cancer cells for a longer period of time. When the photosensitizer in the cancer cells is exposed to a specific wavelength of light, it produces an abundance of oxygen that builds up and kills the cancer cells surrounding the photosensitizer. Because the light must pass through the skin, it can only be used to treat cancer that is less than cm under the skin or body lining. To date, this therapy has only been used to treat esophageal and non-small cell lung cancer. Photodynamic therapy can also be used to treat acne. http://www.moderncancerhospital.com/system/templets/green/static/treatment/photodynamic-therapy.gif Review Questions answer questions on a separate sheet of paper. What is the purpose of photosynthesis?. Why is photosynthesis important to us? 3. What are photoautotrophs? Give 3 examples.. Explain how light energy is converted into chemical energy in photosynthesis. 5. What are the reactants and products of photosynthesis? 6. How many hydrogen atoms go into photosynthesis? How many come out of photosynthesis? 7. How many carbon atoms go into photosynthesis? How many come out of photosynthesis? 8. How many oxygen atoms go into photosynthesis? How many come out of photosynthesis? 9. How can photosynthesis be used to produce medications? 0. What is photodynamic therapy and how can it be used to treat cancer? 06
Name(s): Period: Date: HASPI Medical Biology Lab 06 Adapted from The Floating Leaf Disk Assay for Investigating Photosynthesis by Brad Williamson. Scenario You are a medical research scientist team for HASPI Pharmaceuticals. You have been tasked with determining which plant leaves will be the most effective in producing a new medication to treat diabetes. The most productive plant leaves will undergo photosynthesis the fastest. Your team will use the leaf disk assay procedure to determine the rate of photosynthesis of different leaves. An assay is analysis, often of a drug, to determine the presence, absence, or quantity of one or more components. Materials 0.% CO solution Straw 3 Plastic cups Syringe Timer Leaf A Leaf B Leaf C Light source Paper towels Marker Graduated cylinder Procedure/Directions Your lab team will be given tasks, or directions, to perform on the left. Record your questions, observations, or required response to each task on the right. Part A: Set-up Task Obtain the following supplies for your lab team: 3 Response a. Hypothesis 300 ml of 0.% CO solution (in a beaker) 3 plastic cups straw syringe paper towels timer Your teacher has provided samples of different types of leaves from a variety of plants. Choose and collect leaves from 3 of the plant options. Hypothesize which leaf will undergo photosynthesis the fastest and record the type of leaf. Label the plastic cups A, B, and C. Measure and pour 00 ml of CO solution into each cup. Leaf A: Leaf B: Leaf C: Place the leaves on paper towels. Use the end of the straw to cut out 0 small circles from each leaf. Try to stay away from any large veins in the leaf. Make sure each circle is whole and keep them in separate piles for each leaf type. 07
Part B: How Is This Going to Work? Answer the following questions before proceeding. Each leaf disk contains air spaces and a. What does a plant need for photosynthesis? plant cells capable of performing photosynthesis.. Plant cells need carbon dioxide (CO), water, and light to produce oxygen b. What do plants produce through photosynthesis? (O) and glucose through photosynthesis. 3. You will be providing the leaf disks with carbon dioxide and water in the CO solution. The light source will be a lamp c. Explain how you are providing the following for the provided by your instructor, or direct leaf disks in this experiment: i. carbon dioxide sunlight.. The leaf disks are saturated with the CO solution, which causes them to sink ii. water to the bottom. (Do not add leaves yet.) 5. As the leaf disks are exposed to light iii. light they will perform photosynthesis, and therefore start producing oxygen and glucose. 6. As the oxygen is produced, it will fill in d. Explain how you are able to compare the rate of the spaces in the leaf disk. Once photosynthesis between the three leaves in this experiment. enough oxygen has been produced, it will cause the leaf disk to float to the surface of the solution. 7. Different types of plants have different rates of photosynthesis. By comparing how quickly the leaf disks float to the surface, we can infer which plant would have the faster rate of photosynthesis. Plant cells Leaf disk 08 http://www.elbiology.com/images/basis.jpg
Name(s): Period: Date: Part C: Forcing CO Solution Into the Leaf Disks 3 5 6 The first thing your team needs to do is fill those air spaces with the CO solution. Remove the plunger from the syringe and gently place the 0 disks from leaf A into the syringe. Replace the plunger gently and push it until only a small amount of air and the leaf disks are left. DO NOT SMASH THE LEAF DISKS! From cup A, pull approximately 3-5 ml of CO solution into the syringe with the leaf disks. Cover the opening of the syringe and lightly pull back the plunger to create a vacuum. Hold the vacuum for 0 seconds and then release it. The vacuum will force the CO solution into the air spaces of the leaf disks and the disks will float to the bottom of the syringe when they are full of CO solution. You will have to repeat the vacuum and release a few times until all of the leaf disks remain at the bottom of the syringe. IF all of the disks have not sunk to the bottom after vacuum attempts, add one drop of liquid soap to the solution in the syringe and repeat steps and 5. Soap coats the surface of the leaf, allowing the CO solution to be more easily pulled into the leaf. Part D: Measuring Photosynthesis 3 5 6 Remove the plunger from the syringe and pour the leaf disks and solution into cup A. The plant cells within each leaf disk are capable of performing photosynthesis and producing oxygen. The only things they need are CO, water, and light. You have provided CO and water in the CO solution. The only item you need now is the light source. a. What does the leaf disk need to perform Your teacher may provide a lamp as the light source, or you can place the cup in direct sunlight. photosynthesis? Take cup A to the light source. As soon as the cup is placed in the light source, start the timer. As the plant cells perform photosynthesis, they b. What do the leaf disks produce through photosynthesis? produce sugar (glucose) and oxygen (O). As the O is produced, it will push the CO solution out of the spaces in the leaf. Once enough O has been produced, it will make the leaf float to the top of c. Why do the leaf disks float to the surface? the cup. The faster the leaf disks float to the top, the more photosynthesis is occurring. Every minute, record the number of leaf disks that have floated to the top in Table. Stop recording when either 5 min. has elapsed, or all of the leaf disks have floated to the top. After each minute, gently swirl the cup to make sure none of the leaf disks are sticking to the sides or bottom of the cup. 09
7 Repeat Part C and Part D for leaf disks B and C. If you are in a team, one member can watch and record the times for Cup A, while the other members prepare and run the lab for leaves B and C. Analysis & Interpretation Answer the following questions using data from your lab AND internet research if needed. Table. Leaf Disk Assay Time (min) Leaf A: Leaf B: Leaf C: 0 3 5 6 7 8 9 0 3 5 Create a graph comparing and contrasting the time it took the leaf disks to float between leaves A, B, and C. Do not forget a title and to label your axes. 0
Analysis Questions answer questions on a separate sheet of paper. Which leaf disks had the fastest rate of photosynthesis? Explain your answer.. Which leaf disks had the slowest rate of photosynthesis? Explain your answer. 3. Which plant would your research team recommend be used to produce the new medication? Why?. List and explain at least two variables that could have impacted your results. 5. What three components were needed to make the leaf disks perform photosynthesis? 6. What two components were produced by the leaf disks during photosynthesis? 7. Which component produced were you observing in this lab? How were you able to observe this? 8. What is the chemical reaction that occurred in the leaf disks? (HINT: What are the reactants and products?) 9. What do you think would happen if you removed the leaf disks from the light source? Explain your answer. NOTE: Plants are capable of both photosynthesis AND cellular respiration. 0.Research and find at least one plant example that can be used medically. Describe what part of the plant can be used as a drug, what it is used to treat, and how it works. Connections & Applications Your instructor may assign or allow you to choose any of the following activities. As per NGSS/CCSS, these extensions allow students to explore outside activities recommended by the standards.. RESEARCH AND CREATE A WEBSITE: Go to the following site and register to create a free website: www.webs.com (if you have another free website resource you would rather use, you may use that instead). Create a website with 5 pages. Each page will have the following topic: a. Page : Outline the process of photosynthesis, focusing on what is needed for photosynthesis to occur and what is created in photosynthesis. b. Page : List of 5 plants/herbs commonly used in medicine, and what conditions they are used to treat. c. Page 3: How can photosynthesis be used to create medicines? d. Page : How can photodynamic therapy treat cancer? e. Page 5: How can photodynamic therapy treat acne? A minimum of paragraphs (-5 sentences each) is needed for each page. Use at least digital media resource for each page (table, graph, audio, video, or interactive animation) to enhance your presentation and support the page topic. ALL of the information must be in your own words and resources correctly cited at the bottom of each page, including the digital media resources.
. CALCULATING THE RATE OF PHOTOSYNTHESIS: Use the following information to calculate the rate of photosynthesis. One of your research associates conducted a leaf disk assay on a rare species of orchid that is believed to have a very high rate of photosynthesis. This plant is also rumored to have a high rate of cellular respiration, which could negate the high rate of photosynthesis. Analyze the following graphs and answer the questions below to determine the gross rate of photosynthesis. Graph. Light Exposure (Photosynthesis) 0 Graph. Dark Exposure (Respiration) 0 Percent (%) 8 6 Percent (%) 8 6 0 3 5 6 7 8 9 0 0 3 5 6 7 8 9 0 3 5 6 Time (min) Time (min) Graph has the results for the percentage of leaf disks that floated to the surface each minute. In order to calculate the rate of photosynthesis, you need to know the time (min) at which 50% of the leaf disks rose to the surface. This is called the Estimated Time 50-light, or ET50-light. What is the ET50-light? As the plant cells undergo respiration, they use the oxygen that was created in photosynthesis, causing the disks to drop. Graph has the results for the percentage of leaf disks that dropped to the bottom each minute. The ET50-dark is the time (min) at which 50% of the leaf disks dropped to the bottom. What is the ET50-dark? a. Use the ET50-light and ET50-dark to complete the following equation and determine the rates of photosynthesis and respiration. Rate of respiration = = = ET50-dark min - Your calculations Answer Rate of photosynthesis = = = ET50-light min - Your calculations Answer
b. Use the following equation to determine the relative and gross rate of photosynthesis. The gross rate of photosynthesis takes into account any cellular respiration that may have occurred. This is important since the products of photosynthesis (oxygen and glucose) are used in cellular respiration. Relative rate of = min - + min - = min - photosynthesis Rate of respiration Rate of photosynthesis Answer min - Relative rate of photosynthesis Gross rate of photosynthesis = = min - Answer Rate of photosynthesis c. A gross rate of photosynthesis that is, for example, would signify that photosynthesis occurred at times the rate of respiration. If the gross rate of photosynthesis is negative, it would mean that respiration is occurring at a greater rate than photosynthesis. What does the gross rate say about the photosynthesis rate of the plant that was tested? d. The researcher also collected data from a young leaf and an old leaf. Young Leaf Old Leaf ET50-light ET50-dark ET50-light ET50-dark 0.93 0.06 0.78 0.03 Determine the gross rate of photosynthesis for the young and old leaf. Does the young leaf or the old leaf have a greater gross rate of photosynthesis? Explain your answer. 3. EXTENDING THE EXPERIMENT: Choose one of the following questions to create your own experiment: a. Does the amount or type of light affect the rate of photosynthesis? b. Does the age of the leaf affect the rate of photosynthesis? c. Does the amount of carbon dioxide in the solution affect the rate of photosynthesis? Using the same leaf disk assay model, create and perform an experiment to test one of the questions above. Create a lab report that includes the question, your hypothesis, materials, procedure (step-by-step), and a table summarizing your results. NOTE: You may need to check out supplies (such as a syringe) from your instructor. To make the 0.% CO solution at home, add 0.6 grams (approximately /8 tsp) and drop of liquid soap to 300 ml of water. Resources & References Armstrong, J. E. 995. Investigation of Photosynthesis Using the Floating Leaf Disk Assay. http://www.bio.ilstu.edu/armstrong/biolab/cellbio/psynex.htm. Dolmans, D.E., Eukumura, D., and Jain, R.K. 003. Photodynamic Therapy for Cancer. Nature Reviews Cancer; 3(5); 380-387. Williamson, B. 00. The Floating Leaf Disk Assay for Investigating Photosynthesis. Exploring Life Community, http://www.elbiology.com/labtools/leafdisk.html. 3