Photosynthesis Lab: Floating Leaf Disks.docx



Photosynthesis Lab: Floating Leaf DiskIntro: Photosynthesis is a process that converts carbon dioxide into sugars such as glucose using energy from the sun. When light is absorbed by pigments in a leaf, the energy absorbed is used to incorporate the carbon dioxide into organic molecules in a process called carbon fixation.The process of photosynthesis can be expressed by the following word equation and chemical equation.Carbon dioxide + Water ---> Glucose + Oxygen6CO2 + 6H2O ----> C6H12O6 + 6O2In this lab, you will be using leaf disks, to assay the net rate of photosynthesis under various lighting conditions. Leaf disks normally float; however, when the air spaces are infiltrated with carbon dioxide, the overall density of the lead disk increases and the leaf disk sinks. When sodium bicarbonate (baking soda) is added to the water, the bicarbonate ion acts as a carbon source for photosynthesis causing the leaf disk to sink. As photosynthesis proceeds, oxygen is released into the interior of the leaf, which changes its buoyancy causing the disk to rise. Since cellular respiration is taking place at the same time in the leaf, oxygen generated by photosynthesis is consumed. As a result, the rate that the disks rise is indirectly proportional to the net rate of photosynthesis. Describe in your own words and in complete sentences the purpose of this lab:Procedure: 1. Get 1 plastic cup. You will use this same cup for the Light, Ambient Light and Dark trials.2. Mix 1 gram of sodium bicarbonate into 100 ml of water into a beaker.3. Hole punch 30 uniform leaf disks using the end of a straw. Avoid cutting through any major leaf veins. You will need 10 disks per trial.4. Remove the plunger of the syringe and place 10 leaf disks in the syringe barrel.5. Replace the plunger being careful not to crush the leaf disks. Push on the plunger until only a small volume of air and leaf disks remain in the barrel.6. Draw a small volume of the sodium bicarbonate solution into the syringe. Invert the syringe and tap the syringe to suspend the leaf disks in the solution.7. Push the plunger to remove as much air as possible. You may need to continue tapping to get the air to rise to the top of the syringe. You may also need to push a bit of water out of the syringe. Please do this over the sink and or clean up your mess.8. Hold a finger over the syringe opening and draw back on the plunger to create a vacuum. Hold this for 10 seconds while swirling the syringe to further suspend the leaf disks in solution.9. Let off the vacuum and repeat the last two steps if needed 2-3 more times until all leaf disks sink. If leaf disks do not sink, add more soap to the bicarbonate solution.10.Pour the disks and solution into the labeled cup.11. Add the bicarbonate solution until the cup is ? full12. Place the cup under one of the light conditions and begin timing.13. Record the number of floating leaf disks at the end of each minute in the provided table below.14. Gently swirl the cup and use your straw to dislodge any leaf disks that are stuck to each other or the side of the cup.15. Repeat steps 5 - 15 for the other two light conditions.16. For the dark trial, wrap the beaker in something to keep the leaf disks in the dark. For the light trials, place the plastic cup under the lamp and for the ambient light condition, just keep the light in the normal classroom light.LightAmbient LightDarkTime(min)# Leaf DisksFloatingTime(min)# Leaf DisksFloatingTime(min)# Leaf DisksFloating111222333444555666777888999101010111111121212131313141414151515161616171717181818191919202020longerlongerlongerPredictions: How will the different light conditions affect the rate of floating leaf disks?Analysis: Please write in complete and understandable sentences.1. Go to and create a graph for each of the three trials. Make sure to choose the correct kind of graph to use for this data. Make sure to also title the graph and label the x and y axis of the graph.Light Graph:Ambient Graph:Dark Graph:2. What was the role of the sodium bicarbonate in the experiment?3. Which trial resulted in all the leaf disks floating to the surface the fastest?4. Explain the process that caused the leaf disks to rise. Make sure to use vocabulary from our photosynthesis notes and write in complete sentences.5. If the leaf disks were boiled, what kind of result would you expect? Use your photosynthesis notes to help you with this answer.6. How does light intensity affect the rate of photosynthesis?7. Design an experiment using the same setup to investigate a different variable in the rate of photosynthesis. 7a. In few complete sentences, explain what you plan to do in your experiment.7b. What is your hypothesis?7c. What is your independent variable?7d. What is your dependent variable?7e. What are your controls?7f. How will you collect the data?RHS Summary: RERUNRestate: Restate the objectives or purposes of this lab.Explain: Explain what you did.Results: State your results.Uncertainties: What were some possible errors that could have been made?New Information: State 2 new things or vocabulary you learned. Include a description of what you learned or the definition of the vocabulary. ................
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