Carbon Fixation in Elodea Analysis

1. The phenol red changes color when bubbles are blown into the tube because we exhale carbon dioxide. When the CO2 in our exhaled breath dissolves into the water it forms carbonic acid, which acidifies the water. Since phenol red is a pH indicator, it turned to a urine yellow color when the water became more acidic (pH<7) and its hydrogen ion concentration increased, indicating the presence of CO2 necessary for carbon fixation.
2. When we were blowing bubbles into the water, it took around 5 to 10 (max.) seconds for the water to turn yellow, which means the carbon dioxide dissolved quickly into carbonic acid. However, the fact that it took longer for the Elodea to fixate the carbon would be subject to other variables besides the amount of CO2 we blew into the water.
3. Although the light independent stage of photosynthesis is, indeed, light independent, the energy needed to fixate carbon is derived from the light dependent stage of photosynthesis. Therefore, the plants were placed under the grow lights in order to indirectly supply the energy for the light independent stage of photosynthesis.
4. We saw no change in the color of the phenol red test tube without any elodea, most likely due to the fact that there was no plant in it to fixate the carbon so the carbonic acid was just left to sit there and make  the water acidic.
5. Carbon fixation does not occur in humans or any other heterotrophs. Only autotrophs (which all of earth depends upon for energy) make their own food and can create energy from inorganic molecules. Almost all plants are autotrophs, but even fungi are not producers.
6. Plants don't eat carbon. They take the inorganic molecules of Carbon Dioxide and reduce them to organic molecules that supply energy for them and all other biological organisms. Carbon fixation, personally, is easiest described as the process of "fixing" inorganic molecules and making them organic, or synthesizing sugar from CO2.
7. The controls in this experiment were the tube with only phenol red and the covered tube with elodea. Since the purpose of the experiment was to observe carbon fixation and the conditions needed to stimulate the synthesis of monosaccharides, the color of the phenol red in the tube exposed to the grow light could be compared to the covered tube (and that tube could be compared to the phenol red tube) in order to demonstrate that the light independent stage of photosynthesis is, in actuality, dependent on the energy generated during photosynthesis, and also that without carbon fixation the carbonic acid stayed in the water as indicated by the yellow coloration in the phenol red only tube. Without controls, variables cannot be isolated and conclusions cannot be accurately drawn from experiments. When a variable is changed, we still need something to compare it to in order to observe the effect of that change--the control serves that purpose.