This activity will take you through the impact of phytoplankton and zooplankton on CO2 and dissolved oxygen (DO) levels in an aquatic environment.

Purpose

In this activity, you will see the processes of photosynthesisand respiration at work. You will be comparing plants to animals and observing the water chemistry changes they cause over time.

Hypothesis

In comparing CO2 and dissolved oxygen (DO) valuesin vials containing brine shrimp (animals) and elodea (plant), explain how you think the values may change over time.

Procedure

• Obtain 4 sample bottles- label them as follows….
• brine shrimp, light
• elodea, light
• brine shrimp, dark
• elodea, dark
• Fill all four bottles with DI water to equal volumes
• Take initial values for CO2 , DO and temperature in all four sample bottles and record on data table
• In each of the four vials, place the specified organism as per labels (1 and 3 brine shrimp/ 2 and 4 elodea)
• Carefully place vials 1 and 2 in the water bath under the light
• Carefully place vials 3 and 4 in the water bath in the dark
• Continue taking CO2, DO, and temperature values in each sample bottle every day for five days and record data on data table.

Data

		1- Brine shrimp (light)		2- Elodea (light)		3- brine shrimp (dark)		4- elodea (dark)
DAY	CO2	DO	CO2	DO	CO2	DO	CO2	DO
0
1
2
3
4
5

Analysis

• Construct a graph of day vs. CO2 for samples 1-4.
• Construct a graph of day vs. DO levels for samples 1-4.
• Why were the samples put in both the light and the dark?
• What happened to the CO2 levels over the five days in the dark and light brine shrimp vials?
• What happened to the CO2 levels over the five days in the dark and light elodea vials?
• What happened to the DO levels over the five days in the dark and light brine shrimp vials?
• What happened to the DO levels over the five days in the dark and light elodea vials?
• Explain how the process of respiration relates to the results in the brine shrimp vials.
• Explain how the process of photosynthesis relates to the results in the elodea vials.
• What would happen to CO2 and DO levels in the ocean if the number of phytoplankton (plants) decreased?
• What would happen to the CO2 and DO levels in the ocean if the number of animals increased?

Conclusion

Formulate a thoughtful conclusion to this experiment written in paragraph form. The conclusion should consist of the following…

• Restate your initial hypothesis
• Was your hypothesis correct or incorrect?
• Restate (sum up) the data collected for both the krill and the elodea on DO and CO2.
• Explain possible errors that may have altered your experimental outcome.
• What did this experiment teach you about plants and animals and how they contribute to DO and CO2 levels.