II.) Introduction / Objective
Photosynthesis is the process by which chlorophyll – containing organisms – such as green plants, algae, and some bacteria – capture energy from light and convert it to chemical energy. For the process of photosynthesis to take place the organism must contain chloroplasts. Chlorophyll is responsible for the green color in plants and is also responsible for their ability to photosynthesize. Photosynthesis is usually carried out in the leaves of green plants, but it can also take place in other parts of the plant such as the stem. The balanced chemical equation for photosynthesis is:
Sunlight + 6CO2 + H2O –yields-C6H12O6 + 6O2
The purpose of this lab is to answer the question, Is sunlight required for photosynthesis?
III.) Experimental Design / Materials and Methods
The first experiment was called Separating Plant Pigments. In this first experiment the materials that you need are a piece of green plant (collard greens), a piece of chromatography paper, solvent, and a test tube. The first thing you do is take your green plant and fold it up tightly. Second, you lay the plant on the chromatography paper and smash parts of the plant onto the paper. Next you mark the outside of the tube with a wax pencil where the bottom of the pigments are. Then we take the paper back out of the tube and add the solvent to the bottom of the test tube. Next we have to wait fifteen to twenty minutes for the see what will happen to the paper. The purpose of this experiment is to see how many different pigments will separate from the green plants.
The second experiment was called Detecting Carbon Dioxide Absorption in Green Plants. In the second experiment that was conducted the materials needed are three large test tubes, some Elodea plants, bromthymol blue solution, and a piece of tin foil. The first thing you do is place pieces of the Elodea plant in two of the test tubes. Second you add the bromthymol blue solution, which is a carbon dioxide indicator, to the test tube nearly to the top. The third tube is filled with bromthymol blue solution and is used as a control so that you can compare color change. Next you wrap one of the Elodea containing tubes in tin foil so that it does not receive sunlight. The other Elodea containing tube should be placed in the light. All should remain this way for a twenty-four hour period. The purpose of this experiment is to detect when carbon dioxide is released or gained.
The third experiment is called Detecting Starch in Leaves. Starch is not a result of photosynthesis, but we think that it came from sugars produced during photosynthesis. The materials needed for this experiment are a hot plate, two small beakers, water, ethanol, a leaf from a Coleus plant exposed to light; a light deprived plant, and an iodine solution. The first thing you do is boiling the light exposed leaf in water for one minute. Next you boil the same leaf in ethanol for one minute or until the leaf has turned white. Take the leaf out of the ethanol and place it on a small petri dish and soak it in the iodine solution. If the plant contains starch the color of the iodine will change from a rusty red color to a dark purple or black. Next you take the light deprived plant and boil it for one minute in water. Take it out of the water and place it in the ethanol solution and boil it for one minute. Take the leaf out of the ethanol and place it on a small petri dish and cover it in iodine. The purpose if this experiment is to detect starch in green plants.
In the first lab that was conducted our results came out positive that light is required for photosynthesis to occur. In this experiment I had three color pigments to separate out on to the chromatography paper. Photosynthesis was present in these because the pigments contained chlorophyll a, which plays an important part in photosynthesis. The other pigments contained carotene and xanthrophylls, which are both present in photosynthesis.
In the second experiment we used Elodea plants and a carbon dioxide detecting solvent to see when carbon dioxide is released or gained. In the first tube with the Elodea wrapped in tin foil, so that it could not receive light, the plant gained carbon dioxide during aerobic cellular respiration and turned the solvent yellow. In the control tube the solvent remained the same color because carbon dioxide was not gained or released. In the tube that was kept under the light carbon dioxide was lost and the color changed to a dark blue. This release of carbon dioxide under light proves that light is required from photosynthesis.
The third experiment that we conducted was to see if starch was found in the leaves of green plants. In the plant that was exposed to light starch was found. This proves that photosynthesis was taking place because the plant was producing sugar. In the plant that was deprived of light there was no starch found which proved that photosynthesis did not occur. The plant had to use its stored starch as a source of food.
My interpretation of all these experiments is that yes some type of light energy is required for photosynthesis to occur. In every experiment conducted photosynthesis was present when there was light. In the experiments where light was not present the plant was not producing food or carbon dioxide. In conclusion these experiments prove to me that some type of light is required for photosynthesis. If there is no source of light the plant had to use its stored food to survive. Without light the plant could not survive very long after it had used all of its stored food and energy.