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Educator Resources
Photosynthesis
Equipment Set-up Data Collection
    Procedure		 Data
    Analysis		 Conclusions and
    Extensions

 

Purpose:

In this experiment, we will use the Dissolved Oxygen (DO2) Sensor to measure and determine any difference in the level of DO2 in water, using plants of different types and sizes. We’ll also see if increasing or decreasing light intensity has an effect on rate of photosynthesis and DO2 levels

Background Information:
Through the process of photosynthesis, plants harness light energy from the sun and turn it into chemical energy. In this process, green plants use sunlight to convert carbon dioxide (CO2) dissolved in water to sugars and oxygen. In the case of aquatic plants, the oxygen produced can be dissolved in the water and can then be used by fish and other aquatic organisms. In addition to the amount and type of plants in a waterway, light intensity is another key factor of importance for photosynthesis. Certain wetland environments around the world are experiencing severe losses in underwater vegetation. A decrease in intensity of light is one possible factor that could be responsible for this vegetation loss.

Equipment:

  • PASPORT Dissolved Oxygen Sensor  
  • PASPORT USB Link  
  • Two different types and sizes of underwater plants (i.e. elodea)
  • 250 ml Beakers (with Rubber stopper)
  • 1000 ml Beakers
  • Light source (i.e. Lamp)
  • Dark colored cloth
  • Magnetic stirrer and stir bar (Optional)

Equipment Set-Up:

  1. Connect the USB Link to your computer’s USB port.
  2. Connect the Dissolved Oxygen Sensor to the USB Link.
  3. Fill the 250 ml beaker with water and place one plant inside.
  4. Remove the soaker bottle from the DO2 Electrode and carefully insert into the rubber stopper.
  5. Insert the rubber stopper into the 250 ml beaker, and place inside the 1000 ml beaker.
  6. Add water to the 1000 ml beaker to help keep the smaller beaker from heating up.
  7. If you’re using a Magnetic Stirrer, use the highest setting and make sure there are no air bubbles or plant leaves touching the sensor tip.
  8. Wait about 5 minutes for the system and sensor to reach equilibrium.

    9.  

Data Collection Procedure:  

1. If DataStudio is not already running, it will launch once the USB Link is connected to the computer.

2. Click on the "Launch DataStudio" icon in the PASPortal window.

3. Turn on the light source (i.e. Lamp) and point at beakers.

4. Click the Start button () to begin collecting data.

5. Record data for 10 minutes, then turn off the light and cover the beaker with the dark colored cloth.

6. Record data for an additional 10 minutes.

7. Click the Stop button () to stop collecting data.

8. Repeat steps 3-7 for each of the other plant types and sizes.

 

Data Analysis:

1. Scale the axes to fit the data using the Scale to Fit button () in the Graph toolbar.

2. Examine the graph and study the data.

3. Enter annotations noting the point when you turned off the light and covered the beakers with the cloth.
   a. Click the Annotate button ( ), and enter your text.

 
Conclusions and Extensions:

  1. What happened to dissolved oxygen levels after you turned on the light?
  2. What happened to dissolved oxygen levels after you turned off the light & used dark cloth?
  3. Did you notice different dissolved oxygen levels with different sizes of the same plant?
  4. Were there significant differences between the different types of plants? Explain what could have caused these differences.
  5. How do rainforest plants that are shielded by the canopy successfully adapt to conditions of less direct sunlight?
This experiment is brought to you courtesy of PASCO. 

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