Investigation 5: Photosynthesis Lab

Investigation 5: Photosynthesis Lab
Introduction:
We are now learning about photosynthesis, the process in which all plants receive energy from. By consuming sunlight, water, and carbon dioxide, the plant will be able to produce ATP, NADPH, carbohydrates, oxygen, and water. This is seen in the chemical equation for photosynthesis 2H2O + CO2 + Light -> carbohydrate + O2 + H2O. Ultimately, photosynthesis provides energy for all life on earth by using sunlight to create energy for plants.


In this experiment we will be investigating the rate of photosynthesis of leaf disks placed in cups filled with a bicarbonate solution. As photosynthesis occurs and oxygen is produced the leaf disks float towards the surface of the cups. We can test the rate of photosynthesis by timing how long it takes for the disks to reach the top of the cup. We will test the rates of these leaf disks by covering the cups with different colored cellophane paper. We will be using red and green pieces of cellophane paper to see how the color of the paper affects the rate of photosynthesis of the leaves.


I believe that the cup covered with red cellophane will be the best for producing oxygen and will have a higher reaction rate because the plants are able to absorb the color red since they reflect the color green.
Materials:
  • Baking soda
  • Liquid soap
  • 2 plastic syringes without needle
  • Living leaves
  • Hole puncher
  • 2 clear plastic cups
  • Timer
  • Light source
  • Red and green pieces of cellophane paper
Procedures:

  1. Put 15 grams of baking osda in a bicarbonate solution which will act as a source of carbon dioxide
  2. Pour it in both of the plastic cups, which already contain water
  3. Add a drop of dilute liquid soap solution into each cup, this is used as a wetting agent that will help the leaves perform photosynthesis
  4. Hole punch 10 leaves for each cup (20 total)
  5. Draw air out of spongy mesophyll tissue - allows for a more efficient way to get oxygen in the tissue when photosynthesis occurs, making the disks float
    1. Remove the piston and put 10 disks within the syringe
    2. Replace the plunger without crushing the disks
    3. Put a small volume of sodium bicarbonate into each syringe until the disks are suspended in the solution
    4. Create a vacuum in the plunger by drawing the air out - pull plunger out with finger on opening for 10 seconds, then spring it back
  6. Pour the disks and solution back into the cups
  7. Cover one cup with a sheet of red cellophane paper and the other cup with green cellophane paper
  8. Put both cups under the light and start timing, measure the amount of disks floating for each one minute interval
  9. Record observations
  10. Clean up work station

Pictures:
The cups with solution and leaf disks at 0 min

1 min

2 min

3 min

4 min

Graphs:

Number of leaves rising
Red
Green
White
1 minute
0
0
1
2 minutes
1
0
1
3 minutes
1
0
3
4 minutes
1
0
4

Results / Conclusion:
At the end of experiment, we concluded that the white, unfiltered light had the best effect and rate of photosynthesis for the leaves. The red light was second best and the green light was the worst. This is what we believed would happen because since the leaves already reflect the color green, they would not photosynthesize as fast when being hit by a green light.

However, this experiment did not prove as accurate as we wanted. Because of the limited time restraints, we were only able to time the experiment for 4 minutes, which is very short. Perhaps with more time we could have gotten more accurate readings for this experiment.

Next, we also believe there was an error in creating the sodium bicarbonate mix, or in the way we set up the water within the cups that could have affected the experiment. Human error caused the cups to have different amounts of baking soda and soap which also could have skewed our results.

By doing this experiment we learned more about the rates of photosynthesis and how different colored light affects this rate. Now we know that white, unfiltered light works the best for the plants to photosynthesize.

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