Photosynthesis is a process in which plants use light, water, and carbon dioxide to produce sugars, water and oxygen. Chlorophyll a and chlorophyll b, in the chloroplasts of a leaf, are responsible for absorbing wavelengths of light for use in photosynthesis with red and blue wavelengths being optimal. Testing for the most productive wavelength of light was done using four separate geranium leaves that were covered by red, green, and blue translucent filters, and black paper. The experimental areas of the leaves were compared to a control area that was left uncovered and a subjective rating from 0 to 5 was given to each area depending on the color seen after adding I2KI solution to the leaf. I2KI solution was used because this solution turns purple in the presence of starch. The red filter showed more starch content overall followed by blue, green, and black paper. The red filter was more successful because it transmitted red wavelengths that were better absorbed for photosynthesis, although the blue filter was also successful. The reasoning for the blue filter not being as successful as the red is not clear. The green filter was less successful because it transmitted light that chlorophyll usually reflects. The black filter was the least successful because it absorbed nearly all of the wavelengths and few were able to transmit into the leaf.
Photosynthesis is the process that plants use to make food. Green plants use pigments called chlorophyll, located in chloroplasts, to absorb the incoming light and use it in the photosynthetic process (Massa, Carabella, & Fornasari, 1997). According to Lawlor (1987), there are two different types of chlorophyll: chlorophyll a and chlorophyll b, that collectively capture almost all of the visible light spectrum yet absorb blue (430-450 nm) and red (640-660 nm) most strongly. The end result of photosynthesis is starch and sucrose, which is used as an energy source for the plant (Massa, et al).
Light is an important factor in photosynthesis and the correlation between color and wavelength must be understood. When white light is put through a prism, it will break up into a spectrum of different colors. The spectrum is divided into wavelengths measured in nanometers and each color corresponds to a range of nanometers. Overheim and Wagner (1982) explain the colors we see as the wavelengths that were not absorbed by an object but were instead reflected back at our eyes. They further explain that a green object absorbs blue (400-500 nm) and red (600-700 nm) and reflects wavelengths in the middle of the spectrum that correspond with the color green. Similarly, blue absorbs green and red (560-700 nm) parts of the spectrum and reflects wavelengths that correspond to blue. Finally, red reflects the red end of the spectrum around 607 nm and absorbs the blue and green parts from 400-580 nm. Black absorbs almost all light and does not reflect or transmit wavelengths (Fehrman & Fehrman, 2004). So far, light can be absorbed or reflected, but it can also be transmitted or passed through the object. The transmitted light is colored as well and will be the colors that were not absorbed (Perkowitz, 1996).
In finding which wavelengths are the best for photosynthesis, this experiment will involve placing black paper and red, blue, and green filters over portions of four separate geranium leaves and letting them absorb white light for one week. The results of the control areas, where light was not filtered, will be compared to the results of the covered areas. Because a result of photosynthesis is the presence of starch, and according to Morgan and Carter (2005), starch turns purple in the presence of I2KI solution, this will be the way that we determine how...