How to Measure Oxygen From Aquatic Plants

Overview

Plants are photoautotrophs (photo=light, auto=self, troph= feed) that convert solar energy and carbon dioxide into nutritive sugars. Plants release oxygen as a byproduct of these photosynthetic reactions. In a well-functioning ecosystem, aquatic plants contribute a significant amount of oxygen. Aquatic plants offset carbon dioxide respiration from sediments in lakes, and they play an important role in constructed wetlands that treat wastewater. They also provide habitat for microbial communities. A simple experiment to measure oxygen from aquatic plants utilizes elodea, a readily available aquatic plant. If you are taking field samples of aquatic plants, apply the same procedure using your own plant material.

Step 1

Cut a fresh edge on the stem of the aquatic plant using the razor blade. Crush the end of the stem with the back of a spoon.

Step 2

Fill the test tube with water. Insert the aquatic plant with the cut-side up. Set the test tube in the rack.

Step 3

Place the lamp 5 cm from the test tube. Wait one minute for photosynthesis to begin. Count the bubbles rising from the plant stem for three minutes. Repeat experiment three times. Average the results.

Step 4

Place the lamp 20 cm from the test tube. Wait one minute for photosynthesis to begin. Count the bubbles rising from the plant stem for three minutes. Repeat experiment three times. Average the results.

Step 5

Place the lamp 5 cm from the test tube. Sprinkle a small amount of baking soda in the test tube to increase carbon dioxide. Wait one minute for photosynthesis to begin. Count the bubbles rising from the plant stem for three minutes. Repeat experiment three times. Average the results.

Step 6

Compare average number of bubbles for each treatment using graphs. Independent variables are abiotic factors (light intensity and carbon dioxide concentrations) manipulated by the experimental conditions; they belong on the horizontal x-axis. Dependent or response variables are biotic factors that react to changing environmental conditions; they belong on the vertical y-axis. In this experiment, the y-axis will be number of bubbles, a relative measurement of oxygen respired by the aquatic plants.

Tips and Warnings

  • While native aquatic plants usually provide benefits for aquatic ecosystems, invasive aquatic plants can alter negatively the nutrient balance. Their exploitation of the water surface can restrict light entering the water, causing a collapse of the aquatic food chain.

Things You'll Need

  • Elodea (water plant)
  • Razor blade
  • Spoon
  • Test tube
  • Test tube holder
  • Dechlorinated water (room temperature)
  • Baking soda (sodium bicarbonate powder)
  • 40-watt lamp
  • Tape
  • Clock or timer
  • Metric ruler

References

  • Burnside Scholastic Academy: Photosynthesis
  • State of Washington: Ecology Department--How to Measure Dissolved Oxygen

Who Can Help

  • Center for Aquatic and Invasive Plants: Plant Management in Florida Waters
  • CRC Sugar: How Do Aquatic Plants Influence Dissolved Oxygen?
Keywords: aquatic plants, science experiments, plant projects, science education, measuring oxygen
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