Floating Leaf Disk Assay Lab

In what color light would photosynthesis happen the fastest?

1. In a beaker, prepare a solution of 300 mL of water and 1/8 teaspoon of baking soda (NAHCO3).

2. Add 1 drop of dilute liquid soap to the NAHCO3 solution. Add more NAHCO3 solution if there are suds present.

3. Cut 50 leaf disks with a plastic straw.

4. Put 10 leaf disks into the barrel of the syringe. Push the plunger down, careful not to crush the disks but pushing as much air out as possible.

5. Put some of the solution into the syringe.

6. With your finger over the tip of the syringe, pull the plunger back, creating a vacuum. While doing this, swirl the leaf disks into the solution. Release the vacuum. Repeat this procedure 2-3 times in order to get the disks to sink.

7. If the disks do not sink after 3 times, add a few more drops of soap.

8. When the disks have sunk, pour the disks and the solution into a clear plastic cup. Add more solution to a depth of about 3 cm. This cup will remain uncovered, as it is the control.

9. Place the cup underneath the fluorescent light and start the timer. At the end of each minute, record the number of floating disks. Continue until all of the disks are floating or until 20 minutes have passed.

10. Repeat the experiment four more times, but cover the other four cups with a different color of cellophane: red, opal, yellow, and green.

Floating Leaf Disk Assay Lab

by Sandra Roddick, Tina Ho, Natasha Sanchez, and Josh Garbarino

Data - Graphs

Data Summary

Hypothesis

The red light caused the disks to rise in the least amount of time (7 minutes). Followed by red was yellow (at 8 minutes), then the control (9 minutes), and then green (12 minutes). The opal took the most time; only 4 disks had risen after 20 minutes.

Average rates:

Red: 10 disks / 7 min = 1.43 disks/min

Yellow: 10 disks / 8 min = 1.25 disks/min

Control: 10 disks / 9 min = 1.11 disks/min

Green: 10 disks / 12 min = 0.83 disks/min

Opal: 4 disks / 20 min = 0.2 disks/min

Data - Tables

If a fluorescent light is covered in red cellophane, then photosynthesis will happen at the quickest rate, and leaf disks will float to the top of a baking soda solution quickly due to oxygen production. Photosynthesis will happen second most quickly in opal-covered light, then in uncovered light, then in yellow-covered light, and finally slowest in green-covered light. This is because the two main pigments, chlorophyll a and b, mostly absorb red and blue wavelengths of light while reflecting yellow and green wavelengths. Therefore, red and blue light would result in more photosynthesis.

Conclusion

Conclusion - Experimental Error

Background

Some possible errors in the experiment include an inconsistency in the distance and angle of the light and the fact that some cups were not completely covered by the cellophane on the sides, so some white light could have gotten into the cup and influenced the rate of photosynthesis. In addition, two different lights were used in order to test multiple cups at once and speed up the experiment.

Conclusion -

Solutions

Some solutions include setting a precise position for the light and keeping it unchanged throughout the experiment, using more cellophane and wrapping the cups on the sides in addition to the tops, and using the same light for all of the cups.

Our hypothesis was somewhat supported by the data. We had predicted that red would result in the quickest rate of photosynthesis and, therefore, the leaves under red light would rise fastest due to the production of oxygen. This was supporred by our data, as the leaves rose the fastest under the red light, at an average of 1.43 disks/min. However, yellow came in second place, doing better than both opal and the control at 1.25 disks/min. Our prediction for the control was supported, as it came in third place with 1.11 disks/min. Green did better than expected, coming in fourth place with 0.83 disks/min. Finally, we had predicted that opal would come in second, but it was actually the slowest, with 0.2 disks/min and only 4 disks floating after 20 minutes.

Background (Cont.)

Photosynthesis takes place inside the chloroplasts, which are in the cells in the mesophyll, or the middle layer of the leaves. The mesophyll is surrounded by the epidermis, which protects the leaves, and the cuticle, a layer of wax on the surface of a leaf that prevents water loss. At the bottoms of leaves are the stomata, where oxygen, carbon dioxide, and water move in and out of the leaf. Spinach leaves, in particular, are thin, which helps maximize sunlight exposure and gas exchange for photosynthesis.

Photosynthesis is a process plants undergo that uses water and carbon dioxide gas in the presence of light energy to produce glucose and oxygen gas. This is represented by the formula: 6CO2 + 12 H2O -> C6H12O6 + 6 O2 + 6 H2O.

Photosynthesis happens within the chloroplasts of a plant cell. Inside each cell are pigments that absorb the necessary light to carry electrons to the photosystems and capture the light energy. Chlorophyll a and b are the primary pigments. They absorb red and blue wavelengths of light and reflect green and yellow wavelengths.

Further experimentation could include studying the effect of temperature by heating and cooling the baking soda solution, studying the effect of additional colors by using more colors of cellophane, such as blue, purple, and orange, and studying the effect of baking soda concentration by lowering and raising the amount of baking soda added to the 300 mL of water.

Conclusion -

Further Experimentation

Procedure

Materials

Big Idea

• Baking Soda (1/8 tsp)
• Distilled Water (300 mL)
• Dilute Liquid Soap
• Spinach Leaves
• Plastic Straw
• Syringe
• Beaker
• Plastic Cups (5)
• Fluorescent Light
• Cellophane (opal, red, yellow, and green)

This lab connects to Big Idea 2: Big Idea 2: Cellular Processes: Energy and Communication.

"Biological systems utilize free energy and molecular building blocks to grow, to reproduce, and to maintain dynamic homeostasis."

The spinach leaves use the free energy given off by the sun lamps to undergo photosynthesis. If the leaves were still attatched, the glucose produced would have helped the plant grow. The byproduct, oxygen, is what caused the disks to float.