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Bri Martin, Eschem Rosenblatt, Sankalp Gupta

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The heart shaped chads had a higher rate of photosynthesis than the circle shaped leaf chads. This is seen as the 1/ET50 is higher for the heart-shaped chads.

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Our prediction was wrong as the heart shaped chads had a higher photosynthesis  rate. We had believed that the circle shaped chads had a higher surface area but it seems the heart shaped ones do. This could be important in understanding the different shapes of leafs. It could also simply be based on the surface area of the leaf. Some errors could be that not enough soap was put in the solution to remove the waxy surface of the leaves. When in the vacuum it could leave some air in the chads.

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Step 1- Prepare 300 mL of 0.2% bicarbonate solution for each experiment. The bicarbonate will serve as a source of carbon dioxide for the leaf disks while they are in the solution.

Step 2- Pour the bicarbonate solution into clear plastic cups to a depth of about 3 cm. Label your cups with your experimental variables. Fill an additional cup with only water to be used as a control group. Label this cup as your control.
Step 3- Using a pipette, add one drop of a dilute liquid soap solution to the solution in each cup. It is critical to avoid suds. If either solution generates suds, then dilute it with more bicarbonate or water solution. The soap acts as a surfactant or “wetting agent” — it wets the hydrophobic surface of the leaf, allowing the solution to be drawn into the leaf and enabling the leaf disks to sink in the fluid.
Step 4- Using a hole punch, cut 10 heart-shaped and circle- shaped leaf chads from a spinach leaf for each cup.

Step 5- Draw the gases out of the spongy mesophyll tissue and infiltrate the leaves with the sodium bicarbonate solution by performing the following steps:

a. Remove the piston or plunger the syringes. Place the 10 leaf disks into each syringe barrel.
b. Replace the plunger, but be careful not to crush the leaf disks. Push in the plunger until only a small volume of air and leaf disk remain in the barrel (<10%).
c. Pull a small volume (5 cc) of solution from your prepared cups into each syringe. Tap each syringe to suspend the leaf disks in the solution. Make sure that, with the plunger inverted, the disks are suspended in the solution. Make sure no air remains. Move the plunger to get rid of air from the plunger before you attempt Step d.

d. You now want to create a vacuum in the plunger to draw the air out of the leaf tissue. This is the most difficult step to master. Once you learn to do this, you will be able to complete the entire exercise successfully. Create the vacuum by holding a finger over the narrow syringe opening while drawing back the plunger. Hold this vacuum for about 10 seconds. While holding the vacuum, swirl the leaf disks to suspend them in the solution. Now release the vacuum by letting the plunger spring back. The solution will infiltrate the air spaces in the leaf disk, causing the leaf disks to sink in the syringe. If the plunger does not spring back, you did not have a good vacuum, and you may need a

different syringe. You may have to repeat this procedure two to three times in order to get the disks to sink. (If you have any difficulty getting your disks to sink after three tries, it is usually because there is not enough soap in the solution. Try adding a few more drops of soap to the cup and replacing the liquid in the

syringe.) Placing the disks under vacuum more than three times can damage the disks.

Step 6- Pour the disks and the solution from the syringe into the appropriate clear plastic cup.

Step 7- Place the cups in your chosen conditions and start the timer. At the end of each minute, record the number of floating disks. Then swirl the disks to dislodge any that stuck against the side of the cups. Continue until all of the disks are floating in the cup.

Step 8-To make comparisons between experiments, a standard point of reference is needed. Repeated testing of this procedure has shown that the point at which 50% of the leaf disks are floating (the median or ET50, the Estimated Time it takes 50% of the disks to float) is a reliable and repeatable point of reference for this procedure.

Step 9-Record your findings.Use your results to prepare a Microsoft Excel graph for a classroom peer review presentation.

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How does the shape of the leaf chad affect the rate of photosynthesis?

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Hypothesis: The circle-shaped leaf chads will have a higher rate of photosynthesis

Prediction: If the leaf chads are circle-shaped then they will have a higher 1/ET50

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[Insert Image of Graph Here]