The Three Experiments on Photosynthesis, Chromatography, and The Wavelength of Light

Three experiments were conducted which correlated with each other. First was to see how starch is only stored when a plant is able to perform photosynthesis. By using iodine, it showed how much starch is being stored. The darker the leaf absorbed by the iodine, the more starch is stored. The second is separating pigments of a plant to see which colors make up the plant. By using the technique of chromatography, the separation of pigments is clearly shown. The final experiment showed the wavelengths of light that are absorbed by the spirulina and geranium. By knowing this, it’s known which colors help the plants perform photosynthesis efficiently

Introduction

Photosynthesis is a cycle that occurs in plants when light energy is used to convert into chemical energy which then provides fuel for other living organisms. During this process, light energy is absorbed a green substance found in the chloroplasts called chlorophyll. This converts the CO2 from the air and water to glucose which releases the oxygen we use to breath. Without light photosynthesis, won’t produce glucose efficiently.

The green pigment of plants is made up of different colors that the plant absorbs. Chromatography is a technique used to see what pigments make up the color of a substance, in this case the color of plants. Chromatography works by placing a dot of a substance onto special chromatography paper and using a solute, it travels up the paper to separate different pigments. Thus, revealing different colors of pigments.

The role of light plays a very important role in plants. Plants are able to absorb specific wavelengths of light which ranges from 380 nm to 700 nm. This spectrum are the colors humans see (red, orange, yellow, green, blue, indigo, and violet.) Violet having the most energy to red having the least amount of energy. Different colors are efficient for the plant to absorb and perform photosynthesis efficiently. Colors like violet/blue and red are most efficient for providing the plant with energy.

Methods and materials

Three separate experiments were conducted. The first one was done by taking two geranium leaves. One was put under a light for 48 hours and the other wasn’t exposed to light for the same duration of time. Then, a beaker filled halfway to about 300 mL with distilled water was placed on a hot plate to boil. After the water was boiled, both leaves were placed to “cook” until it looked like overcooked vegetables. After they were done cooking, both leaves were placed in a beaker and placed again in the water making it a double boiler with ethanol added into the beaker. It was left alone until the leaves were bleached. The leaves were then placed onto a petri dish and iodine was poured into it. The leaves were then left to soak in the iodine.

The second experiment was conducted. Spinach leaves were obtained along with a mortar and pestle and began grinding the leaves. Then a bit of sand, spirulina powder and acetone was poured onto the spinach. With a cheese cloth and a beaker underneath the spinach contents were poured through leaving the liquid. With a wooden stick and chromatography paper, a dot was placed around an inch from the bottom of the paper. This was done ten times to ensure that there was enough concentration of pigment for the chromatography to work. Then with another stick and parafilm, the paper was rolled up and taped with the parafilm. It was taped in a way that the paper was just barely touching the end of the test tube. The paper was placed and chromatography solution was added. It was left alone until the end of the session.

The last final experiment was conducted. With the remaining geranium liquid from the previous experiment, a pipette was used to extract the liquid and put into a cuvette. A Lab Quest spectrophotometer was given out. The machine was turned on and calibrated for this experiment. When the machine was finished calibrating, the cuvette with the geranium liquid was placed. The absorbance of the contents of the cuvette were measured from 380 nm-700 nm. Data was recorded.

Discussion

Iodine is used to find if starch is present. The leaf that wasn’t exposed to light wasn’t able to store starch efficiently. While the leaf that was exposed to light was able to store starch completely. This showed that without light, a plant isn’t able to properly perform photosynthesis.

The chromatography results showed that there were different pigments found in the plant. A light Yellow, a yellow-orange, a blueish-green and a light green pigment were present on the paper with the light green being at the bottom and the yellow being at the top. The plant is mostly composed of dark green pigment.

The graph of the spirulina and geranium both show specific wavelengths where they absorb efficiently. The geranium efficiently absorbed wavelengths of about 420-430 nm and around 650-660 nm. On the electromagnetic spectrum, these would be the colors red-orange (420-430 nm) and blue-violet (650-660 nm). The spirulina was effective at absorbing wavelength of 400-420 nm and around 650-660 nm. These colors were red and violet-blue colors. Although the geranium’s absorbance is relatively higher than the spirulina. At 420-430 nm, the absorbance of geranium is 1.8 and at 650-660 nm the absorbance was 1.1. The spirulina’s absorbance at 400-420 nm is 1.4 and at 650-660 nm is around 0.9. The geranium was better at absorbing the same wavelengths of light as the spirulina.