The Color of the Rainbow as Told by Plants

As stated in my previous post, plants use light energy to photosynthesize. During this process they breathe in carbon dioxide and exhale oxygen. The amount of photosynthesis a plant performs effects the amount of oxygen it respires into the atmosphere. As discovered in the previous experiment, the closer the plant was to the light source played a role in the rate at which a plant respired. The goal of this experiment is see the effects light on the rate in which a plant takes in carbon dioxide versus the rate it respires oxygen. For this experiment we will need:

·       4 test tubes with rubber stoppers

·       A rack to hold the 4 test tubes

·       Elodea plants

·       Distilled Water

·       Phenol Red

·       Bromothymol Blue

·       Light Source

·       Stirring Rod

To begin, each of the four test tubes must be rinsed with distilled water and then filled three-fourths full with distilled water. Using chemical resistant gloves and under adult supervision, carefully put 5 drops of phenol red and 5 drops of bromothymol blue in each test tube. Carefully mix the chemical indicators in the test tube by moving it in an upward and downward motion. Once the chemicals are completely mixed, place equal length sprigs of the Elodea plant in 3 of the containers then seal all four test tubes. Once the test tubes are sealed, remove the chemical resistant gloves and turn them inside out without letting the outer part of the glove touch the skin. Dispose of the gloves in a container marked with “Hazardous Material” for safety. 

 Lightly cover one test tube with an Elodea plant using tissue paper to simulate shade, put an uncovered Elodea plant in total darkness, and one test tube with an Elodea plant and the empty test tube with receive full light. Place the “shaded” test tube, the empty test tube, and the Elodea assigned to full sunlight in the test tube rack. Place the rack with the three test tubes in exposure to the provided light source. Leave the test tubes undisturbed in their assigned lighting until there is a noticeable change in color in the surrounding liquid. In my personal experiment, we waited 48 hours to reevaluate our plants. When a color change has occurred, remove the tissue paper from the shaded plant and return it as well as the plant subjected to darkness to the test tube rack for comparison. The color scale is a spectrum with yellows being the most acidic and blues and purples being the most basic. It is important to note that oxygen is basic and carbon dioxide is acidic. This means that any containers shaded yellow will have a higher level of carbon dioxide and any containers shaded purple will have a higher oxygen level. For example, humans exhale carbon dioxide so if someone was to blow into the same concentration that the plants are exposed to, the liquid would turn yellow.

The results should depict that the full sun and empty test tube containers should remain purple, while the shaded plant is a lighter purple to dark pink color. The plant exposed to complete darkness should have more of a yellow color. This is due to the fact that the plants exposed to full sun should be respiring more oxygen into the surrounding liquid due to its proximity to light as demonstrated in the previous experiment while the plant in darkness should not be respiring much to conserve energy with the shaded plant landing somewhere in the mid-range. My experiment is an anomaly as listed left to right are the full sun, shaded, empty, then total darkness test tubes (shown below). Although the plant that was exposed to full sun is the healthiest looking, it should be in a purple colored liquid rather than bright yellow. The Elodea plant that was exposed to total darkness began to lose its green color and began to wilt which promotes the necessity of a light source for even aquatic plants. If plants are exposed to the proper conditions for efficiency, they should be respiring at a faster rate which would turn the concentration blue. This indicates that if a plant was to respire and carry out photosynthesis at the same rate it should be surrounded by a red or amber concentration. This situation would most likely happen around dawn and dusk because the plant would not be exposed to full sunlight as it would during midmorning, lunchtime, or afternoon when the rate of photosynthesis is at its highest. Similarly, there is no natural light source during night so no photosynthesis would be occurring and the rate of respiration would be at its highest.