The Great Carbon Dioxide Experiment


Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a byproduct. The purpose of this experiment is to see how different concentrations of carbon dioxide affect the rate of photosynthesis in spinach leaves. I hypothesize that the greater the concentration of CO2 the faster the plant spinach leaves will photosynthesize because the formula for photosynthesis is: carbon dioxide+ water cell food+ oxygen where the is light Method

  • Equipment:
  • Dish Liquid Soap
  • Baking Soda
  • 150-watt lamp
  • Spinach Leaves
  • 5 Clear Plastic Cups
  • Hole Punch
  • Permanent Marker
  • Plastic Syringe

Collection of Data:

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Independent Variable: Amount of bicarbonate

Dependent Variable: ET50

Controlled Variable: Spinach Leaves, number of leaves per cup, size of leaves

Step 1: Use the hole punch to cut out ten uniform size leaves for each of the five cups. Therefore there will be no variety in leaf size so there is no variable in the amount of CO2 absorbed.

Step 2: Prepare five different solutions of the varying carbon dioxide concentrations. They will range from .2 mL to 1.0 mL. Cup one will be the control with 2%. The carbondioxide concentration will determine the amount of leaves that will float over a set period of time.

Step 3: in order to wet the hydrophobic surface of the leaf add one drop of liquid soap to each cup, this will allow the solution to be drawn into the leaf and enable the leaves to sink in the fluid.

Step 4: With the plastic syringe draw out the gases of the spongy mesophyll tissue and infiltrate the leaves with sodium bicarbonate solution and then pour the solution into the appropriate cup. By doing this it will cause the leaves to sink.

Step 5: Place the cups under the lamp and record the number of leaves that have floated to the top of the cup each minute. Continue to do this until all the leaves have floated to the top or until there is no activity in the cups anymore. By doing this it will be possible to find the ET50.


As the carbon dioxide concentration was increased throughout the cups the amount of time it took (ET50) 50% of the leaves to float increase. The ET50 of Cup 2 was 8 minutes and the ET50 of Cup 5 was 13 minutes. This data shows that the ET50 increased as the carbon dioxide concentration increased.


From the data collected the hypothesis was rejected because the bicarbonate solution concentration was increased by .2% in each cup the ET50 increased as the concentration increased. It was expected that the ET50 was going to decrease as the carbon dioxide concentration increased.

I do not support these results because of research results found by Southwestern University’s Biology Department it is determined that the rate of photosynthesis does increase (Taub, 2005). This shows that the experiment was incorrectly done perhaps because of sporadic stirring, cups that did not receive equal light concentrations, or that the leaf was stuck in syringe in Cup 4. This experiment’s data is invalid therefore the experiment can be ignored. There were too many errors that occurred to use consider the data.

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