A snail was added to a beaker of water and allowed to respire for 15 minutes. An elodea plant was added to a separate beaker and also allowed to respire for 15 minutes. After the 15 minute period, the organisms were removed from the beakers and a drop of phenolphthalein was added to each beaker. Phenolphthalein remains colorless in acidic solutions, but turns pink in alkaline solutions. After the phenolphthalein was added to each beaker, sodium hydroxide (NaOH) was added drop by drop to each beaker until the contents turned pink. Since CO2 forms a weak acid when in water, the more an organism respires, the more CO2 is produced, the more acidic is the surrounding solution, and the more drops of NaOH are required to turn the solution pink. The following results were obtained for this portion of the experiment.