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  Investigating the Effect of Photosynthesis and
Respiration on Aquatic Chemistry

Both photosynthesis and respiration occur in lake settings. In this lesson you use microcosms and RUSS data to investigate changes in oxygen concentrations that result from photosynthesis and respiration.

As a biology student your teacher has challenged you to demonstrate that photosynthesis and respiration occur in lakes.

Part I - Microcosm Set-up

Knowledge Base
Read the "Introduction to Cell Respiration and Photosynthesis" before beginning the exercises.

Review your knowledge of photosynthesis and respiration. How do these processes affect water quality measures in lakes? Which measures should be analyzed as indicators of photosynthesis and respiration.

Experimental Design
How can you use lab microcosms to demonstrate that photosynthesis and respiration occur in water samples in a lab setting? You have the following materials available for your use.

  • 3 - 8 oz or 250 ml jars
  • 10 - 8 cm sprigs of Elodea sp.
  • 8 - 5 cm fathead minnows
  • oxygen, carbon dioxide, and pH kits (meters may be substituted)
  • a sunny window or a grow light

You need to choose a water quality measure(s) to analyze in your microcosms. Research the effects that respiration can have on water temperature, pH, CO2 and DO using the "Understanding" portion of the WOW web site. Choose a measure that correlates strongly to photosynthesis and aquatic respiration.

Write a procedural plan for testing your hypothesis. The plan should include enough detail that other students could follow it without consulting with you. Include your predictions for the results of your tests.

Data Collection
Record your results. Be sure to carefully follow the directions for using the kits or meters.

Data Management and Analysis
Graph your data and summarize your results. Title your graphs and label legends, axes, and units of measure.

Interpretation of Results
Reflect on some possible explanations for your experimental results. Do the results indicate photosynthesis and/or respiration? Compare results with different student groups. What might account for similarities or differences among results?

Reporting Results
Develop a presentation of your results using the format specified by the teacher: written paper, oral presentation, poster, or multi-media presentation. The final presentation reflects both parts of the lesson.

Part II - Using WOW Technologies

Knowledge Base
Participate in the discussion of lab microcosm results. How might photosynthesis and aquatic respiration affect water chemistry in a lake environment?

Experimental Design
Write a procedural plan for using WOW data to demonstrate that photosynthesis and respiration occur in a lake. Be sure your plan includes directions on the date(s) and depths to use for data collection.

Predict how the laboratory variable(s) you studied will change in a lake environment. Do you expect a different response? Why?

Data Collection
Determine how you will organize and record the data you collect. Using the "Data" portion of the WOW website, collect all of the data you need.

Data Management and Analysis
Inspect the data. Analyze the data for changes in the laboratory variable(s) you studied. Also look for other changes that might correlate to photosynthesis or respiration. Is there a pattern in the data?

Create a graph of your data. Be sure to label axes and include a title and legend.

Interpretation of Results
Consider the results of your microcosm set-up and RUSS data investigation. Compare your results with the equations for photosynthesis and respiration. What are the relationships among data? What does the lab microcosm and lake study show?

Reporting Results
Develop a presentation explaining the effect of photosynthesis and respiration on aquatic chemistry. The presentation can be a written paper, oral presentation, poster, or multi-media presentation. Include your graphs and summaries in the presentation.


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date last updated: Friday October 08 2004