Light energy drives photosynthesis in plants. For light energy to be useful, it must be able to be absorbed by the photosynthetic pigments that are present in the chloroplasts. The pigments in the chloroplasts, chlorophylls a and b, xanthophylls, and carotenes, each absorb different wavelengths of light.
The small range of electromagnetic waves, light, that can be seen by the human eye lies between 380nm and 750nm. Each wavelength between 380nm and 750nm corresponds to a color that can be seen by the human eye, but since color is a subjective value wavelength is used to report scientific findings.
When looking at an apple, we see the color red. We see red because it is reflected, meaning that the pigments in the apple do not absorb the wavelengths that correspond to the color red, but instead the wavelengths "bounce" off them.
The purpose of this experiment was to find and graph the absorption spectrum, the pattern formed by the specific wavelengths of light absorbed by a given pigment, for carotene. Our hypothesis is, the carotene solution will have a weak or no absorption value for the wavelengths that correspond to orange and red light, approximately 750nm-650nm.
Materials and Methods.
In this experiment, a carotene pigment solution was isolated from spinach pigment extract. This was done by separating the pigments of the spinach extract using paper chromatography. The carotene pigment line was cut into small pieces and soaked in 10 ml of acetone to draw the pigment out of the paper and create a carotene solution.
A spectrophotometer was used to measure the absorption value of the pigments at different wavelengths. After properly zeroing and blanking the spectrophotometer, a sample of the carotene solution was inserted into the spectrophotometer and its absorption value was measured and recorded. The carotene solution's absorption value was measured starting at a wavelength of 400nm and then measured successively at increases of 20nm until the wavelength of 700nm was reached.