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.

 

Q: How Do Plants Exercise? A: They Photosynthesize

Plants use light sources to gain energy for photosynthesis. The amount of energy exerted by the plant to preform photosynthesis is directly related to how much it respires such as how breathing becomes heavier after physical activity. In order to visualize this process, you will need:

·       1 250mL graduated cylinder

·       Distilled water

·       Aquatic plant (Cabomba)

·       Scissors

·       Dissecting needle

·       Light source such as a lamp

·       Timer

To prep for the experiment, take one sprig of the Cabomba plant and carefully flatten its fronds against its stem. Fill the graduated cylinder with 200mL of distilled water. With adult supervision, poke holes along the stem using a dissecting needle and cut the bottom of the stem using scissors at an angle. Immediately place the sprig in the graduated cylinder with the freshly cut end at the top. Make sure the entire plant is completely underwater. Place the plant 15 centimeters from the light source for five minutes to equilibrate the photosynthesis process. Then count the number of bubbles released by the plant for 30 seconds. Record the data and repeat two more times at the same distance. After you have recorded three data points for the distance of 15 centimeters. Move the plant 10 additional centimeters away from the light source so that it is a total of 25 centimeters away from the light source. Let the plant equilibrate for five minutes the repeat the 30 second intervals of bubble counting for three trials while recording each data set. After those three data points are recorded move the plant another 15 centimeters so that it is a total of 45 centimeters away from the light source. Once again, leave the plant to equilibrate for five minutes and then count the amount of bubbles produced by the plant over the course of 30 seconds for three data points. After you have three data points each for each distance, compile the data in a table such as Table 1 below which represents my data during this same experiment.

It is important to note that the light source is the control variable, the plants distance from the light source is the input variable, and the number of bubbles produced is the output variable. As shown by the table, the farther away the plant was placed from the light source the amount of bubbles produced decreased. Similarly, the closer the plants are to the light source the better it preforms photosynthesis. Based on this logic, the more efficient the plant is at photosynthesis the more it respires oxygen into the water. Photosynthesis takes energy from the plant such as exercise does a person. People use less energy walking so there breathing is normal, but once the person begins running, their breathing becomes heavier in order to obtain enough oxygen for their muscles. Plants at the 40 centimeter mark can be compared to the walking person. It is undergoing exercise during photosynthesis but it is not very intense. The 25 centimeter mark can be compared to jogging in which the intensity becomes more difficult than walking but not as intense as running. When the plant was placed at the 15 centimeter mark, its job became a sprint and required more energy so the plant respired more than the other two distance marks. 

The results I obtained were rather consistent in bubble production and support my hypothesis that increased distance from the light source would result in a decrease of bubble production. To better my personal results, more than one person should count the bubbles being released during the time trials to improve accuracy. To fuller quantify the amount of oxygen respired by the plant, the graduated cylinder could be sealed and measure the original air pressure. After each 5 minute timer, the air pressure could be measured at each distance. Using the density of oxygen, we can use the change in pressure to determine how much oxygen is actually released at each distance. I also predict that there will be an increase in bubble production if the light source’s power is increased due to an increased efficiency in photosynthesis.