The effects of Light Quality on the Rate of Photosynthesis Measure through Floating Spinach Disks

Essay by rsato8College, UndergraduateA+, April 2004

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This study was undertaken to determine the relationship of different wavelengths of light and the rate of photosynthesis in spinach leafs. The rate of photosynthesis was measured every five min under light colors of white, green, red, blue and yellow under a light intensity of 2000 lux. The rate of photosynthesis was measured by the spinach disk method in which we replaced the air from the disks with sodium bicarbonate using a vacuum. Under photosynthesis, oxygen, a product of photosynthesis, replaced the bicarbonate solution, made the disks less dense and rise to the top. The rate of photosynthesis was the greatest under white light, followed by red, blue, yellow and green, which produced no detectable photosynthesis signifying that chlorophyll reflects, rather than absorbs, green light. White light was also expected to have the highest rate of photosynthesis as it gives the chlorophyll all the colors of light to absorb.

In general, filtered light reduced the rate of photosynthesis because the chlorophyll didn't receive all the different colors of the spectrum it desired as it did in white light to absorb.


Photosynthesis is the ability to convert light energy into chemical energy in the form of sugar (Freeman 2002). The photosynthetic reactions are divided into two sections: light dependent and light independent reactions. In this experiment, we will be dealing with the light dependent reactions. The actual chemistry of the light dependent reaction is with the addition of light: H2O + ADP + inorganic phosphate + NADP+ ¨ 1/2O2 + ATP + NADPH + H.

Light is a necessary input for photosynthesis to take place. Light's electromagnetic radiation carried in photons are absorbed by the photosynthetic pigments in plants. These photons can cause electron excitation to a higher energy level, which can be added to NADP+ form NADPH or...