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Name:___________________________ Class:_______The Floating Leaf Disk LabIntroduction: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 + Light Glucose + Oxygen6 CO2 + 6 H2O + light C6H12O6 + 6 O2Leaf disks normally float, however when the air spaces are infiltrated with carbon dioxide, the overall density of the leaf disk increases and the leaf disk sinks. When sodium bicarbonate is added to the water, the bicarbonate ion acts as a carbon source for photosynthesis causing the leaf disks 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, the oxygen generated by photosynthesis is consumed.Materials:Sodium bicarbonate (Baking soda) Liquid SoapPlastic syringe (10 cc or larger)—remove any needle! Leaf material Hole punch Plastic cups Timer Light sourceTeaspoonBeaker (250mL or larger)Procedure:You will be putting two cups under the light at the same time. One will contain the bicarbonate solution while the other one will be your control and will just be regular tap water. If at all possible, try to do the steps for both of them at the same time. For instance, measure out the water for the bicarbonate solution and place into a cup. Wash out the beaker so there is NO CONTAMINATION, then measure out tap water and pour into a cup. Prepare 200mL of bicarbonate solution within a beaker.Prepare a 0.2% solution. (This is not very much it is only about 1/8 of a teaspoon of baking soda in 200mL of water.)Pour the 200mL of bicarbonate within the beaker into a plastic cup.Add 1 drop of dilute liquid soap to this solution. The soap wets the hydrophobic surface of the leaf allowing the solution to be drawn into the leaf.? It’s difficult to quantify this since liquid soaps vary in concentration. Avoid suds. If your solution generates suds then dilute it with more bicarbonate solution. Cut 10 uniform leaf disks for each trial by use of hole puncher. Avoid major veins.Infiltrate the leaf disks with sodium bicarbonate solution. Remove the piston or plunger and place the leaf disks into the syringe barrel. Replace the plunger being careful not to crush the leaf disks. Push on the plunger until only a small volume of air and leaf disk remain in the barrel (< 10%).Pull a small volume of sodium bicarbonate solution into the syringe.? Tap the syringe to suspend the leaf disks in the solution.Make sure all of the air is out of plunger before doing the vacuum (push up the plunger until a little bit of water come out the top to make sure all the air is gone).Holding a finger over the syringe-opening, draw back on the plunger to create a vacuum.? Hold this vacuum for about 10 seconds.? While holding the vacuum, swirl the leaf disks to suspend them in the solution.? Let off the vacuum.?You will probably have to repeat this procedure 2-3 times in order to get the disks to sink.?If you have difficulty getting your disks to sink after about 3 evacuations, it is usually because there is not enough soap in the solution. ?Add a few more drops of soap.Pour the disks into the plastic cup which contains the original bicarbonate solution.For a CONTROL infiltrate leaf disks with a solution of only water with a drop of soap—NO BICARBONATE! (Follow steps 1-13)Place under the light source and start the timer. At the end of each minute, record the number of floating disks. Then lightly swirl the disks to dislodge any that are stuck against the sides of the cups. Continue until all of the disks are floating.Data Collection:Fill in BOTH data tables and BOTH graphs. Each graph should have YOUR results and the CLASS average results.Done forget to label EVERYTHING that needs to be labeled.Questions:Bicarbonate Solution:How much baking soda did you use?__________________How much water did you use?_____________________How much soap did you use?______________________Control:How much water did you use?_____________________How much soap did you use?______________________Why was the use of a bicarbonate solution important within the lab experiment?What does the word hydrophobic mean? Explain why shaking the leaf disk around within the syringe is important.Why is it important to create a vacuum in the syringe?Qualitative and Quantitative Observations throughout the experiment33655-127000How does light intensity affect the rate of photosynthesis?What would happen if you turned the lights off after the leaf disks had already floated to the top? Why?10.) What would happen if you turned the lights off before the leaf disks started to float to the top?Why?11.) Explain the process that caused the leaf disks to rise in relation to the Carbon and OxygenCycle.Data Collection and AnalysisExperimental GroupGraphMinutesDisks(Floating)143438928194Class Average1234567891011121314Control Group:GraphMinutesDisks(Floating)146207521996Class Average1234567891011121314Discuss your results: (compare your experimental to the class experimental. Do the same for the control groups. Also discuss the differences between the experimental and control groups).12.) At what time were half of the disks floating for your experimental group? _________________At what time were half of the disks floating for the experimental class average group?__________13.) If you were to recreate this experiment what would you test? What would your independent and dependent variables be? Constants?14.) Create a hypothesis using the information generated in question 13.15.) NOW TEST IT! In the space provided on this side and the next page place your procedure, graph, and conclusion for the experiment.PROCEDURE:GRAPH:CONCLUSION: ................
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