Photosynthesis Lab - Analysis

1. Why does the phenol red change color when we blow bubbles into the tube? Phenol red is an indicator in this experiment. What did it indicate?
   
   
   The phenol red changes color when you blow into it, because you are introducing carbon dioxide to the mix. Phenol red changes to yellow in a pH lower than 7, so the solution turning yellow is an indication of an acidic (lower than 7 pH) solution.
   
   
2. How long did it take to observe a color change in the phenol red? What does the color change indicate in terms of the Elodea plant?
   
   
   It took from 45 minutes to an hour for the phenol red to change from yellow back to a reddish color. This change in color indicates that the Elodea plant is performing photosynthesis, and is taking up the carbon dioxide from the phenol red solution.
   
   
3. If carbon fixation occurs during the light independent stage of photosynthesis, why did the procedure call for placement of the test tubes under the grow lights?
   
   
   While carbon fixation takes place during the second half of photosynthesis, which is called light independent, and doesn't directly involve light, it still requires the energy supplied by the light reactions. Because of this, despite being called light independent, carbon fixation usually only occurs during the daytime, and therefore the test tubes in this procedure needed to be placed under grow lights.
   
   
4. Did you see a change in color of the phenol red test tube with no elodea added? Why or why not?
   
   
   No, I did not see any change in the test tube with no elodea added, and did not expect to. This tube was only the control, used to compare the reactions within the other vials to.
   
   
5. Does carbon fixation occur in humans? Can you think of any other organisms that fix carbon?
   
   
   No, carbon fixation does not occur in humans. This process only takes place in Autotrophs, such as other plants, algae, and some bacteria, or organisms that make their own food.
   
   
6. How does a plant use carbon? What is meant by the term carbon fixation?
   
   
   A plant uses carbon, along with water and light, during photosynthesis, to create food for itself in the form of glucose. Carbon fixation means that carbon dioxide, in a gaseous form, is used as the input to output glucose, a solid compound and a biologically useful form of stored energy.
   
   
7. Identify and explain the control in this experiment. What is the purpose in having a control?
   
   
   The control in this experiment was the test tube containing the phenol red solution, but no elodea plant. This was the control, because there was no contaminant in the solution, and so if any color change occurred within the vial, it could be determined that it was not in relation to the elodea plant. However, since no such change did occur, it was used to compare and contrast the changes within the other two test tubes. The point of a control in any given experiment is to have a constant that you specifically know what will/ will not occur, so that you can compare any other changes to the one specific predictable one.