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Name: Celeste B.
Status: student
Age: 13
Location: N/A
Country: N/A
Date: 12/10/2002
Question:
Does the amount of Carbon dioxide present have an effect on the amount of oxygen plants (such as Elodea) produce? I am doing an experiment in which I am trying to answer this question, but my results are a bit strange... the Elodea (plantlike protist) placed in the water with the largest amount of baking soda (representing CO2) is not producing as much oxygen as the one with 2 tsp baking soda *half the amount. Is there a reason why 2 tsp. increased the oxygen produced and 4 tsp. did not increase it as much? Keep in mind that I made sure the following variables stayed constant: temp. and amount/intensity of light.

Replies:
Yes, the amount of CO2 available will affect O2 production:

http://www.agron.iastate.edu/~weeds/Ag517/2000/Unit3/u3limit.html

http://bio.winona.msus.edu/berg/241f99/Labs/Photosy.htm

Anthony Brach, Ph.D

There is another variable you have not accounted for: the pH. Bicarbonate is not exactly the same thing as CO2. Perhaps the Elodea photosynthesizes best within a certain pH range, and adding too much sodium bicarbonate to the medium raises the pH too high.

Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois


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