October, 2003, Biology Experiment:

Photosynthesis and Oxygen

- Purpose
- Background Information
- Equipment & Supplies
- Experimental Procedure
- Data Analysis
- Conclusions and Extensions

PASPORT Oxygen Gas Sensor
(PS-2126)

Oxygen Gas Sensor

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Purpose:

Students will assess how changes in the amount of light available to plants affects photosynthesis by measuring the by-product of photosynthesis, oxygen.

*Note: This experiment requires DataStudio version 1.8.5, available as a free download .

Background Information:

Plants are the mediators of energy on this planet for all other living things. Through photosynthesis, plants convert sunlight energy into organic molecules, forming the basis of food for all organisms. In a series of reactions, light energy, carbon dioxide and water are combined to create food for plants.

Photosynthesis consists of two reactions, the light-dependent and light-independent reaction. The light-dependent reaction of photosynthesis involves using light energy to remove hydrogen atoms from water molecules. The light-independent reaction in photosynthesis involves changing carbon dioxide and hydrogen into organic molecules. While no light is necessary for the second part of the process to occur, light is required to initiate the photosynthetic process.

If the reactants of photosynthesis are water, light and carbon dioxide, the products are carbohydrates (stored plant energy) and oxygen gas. Plants release oxygen into the air as a byproduct of photosynthesis.

There is useful synergy between plants and animals in this reaction. The oxygen evolved by the photosynthesis reaction is a by-product the plant does not use. Humans, on the other hand, require oxygen for respiration and expel carbon dioxide.

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Equipment and Supplies:

For each lab group:

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Experimental Procedure:

Software & Probeware Setup
  1. Ensure that your USB Link, Xplorer or PowerLink is connected to the computer.

  2. Open the pre-configured DataStudio file for this experiment, below: PS Photosynthesis O2.ds. When the file is opened, you should see a graph of O2 Gas Concentration vs. Time as well as a digits display of oxygen gas concentration.

    DataStudio file, "PS Photosynthesis O2.ds":   Windows (.zip file)  |  Macintosh (.sit file)

  3. Connect the Oxygen Gas Sensor to the PASPORT Interface.


Data Collection & Recording

  1. Place a healthy plant leaf inside a container and tightly close the lid.

  2. Securely place the oxygen-sensing element in the hole in the side of the container.



  3. Let the sensor equilibrate for a few minutes before beginning the experiment.

  4. Cover the container with aluminum foil, or cover with an opaque object (such as a box).

  5. Click Start ( ) to begin recording data. Leave the leaf in the dark for approximately 90 minutes. (The change in O2 level may vary by leaf type.)

  6. Click Stop ( ).

  7. Remove the aluminum foil or other opaque cover. Place a lamp 1m from the container.

  8. Turn on the lamp and click Start to begin recording data.

  9. Record data for about 90 minutes, then click Stop.

Data Analysis:

  1. Rename your data runs to the corresponding conditions.

  2. Examine the graph display to view your data, using the Scale to Fit button ( )in the Graph toolbar to resize the axes.

  3. For each run, examine the minimum and maximum values for the concentration of gaseous oxygen.

  4. Select the data run you want to examine and use Linear Fit to determine and compare the slope for each data run.

Conclusions and Extensions:

  1. How did the oxygen levels change when the plant was in darkness?

  2. How did exposure to light affect the oxygen levels in the container?

  3. Discuss both the light-dependent and light-independent reactions of photosynthesis. Use this information to explain the trends you notice in the data. Does this help explain behavior of the leaf being studied?