Effect of Light Intensity and Wavelength on Photosynthesis

Photosynthesis is the essential chemical process by which plants convert sun’s radiant energy into chemical potential energy of their organic molecules. It is the most important process for life on the planet earth because plants and nearly all living animals are dependent on this process either directly or indirectly for providing their foods (Hall and Rao). Apart from few microorganisms, only plants can utilize sunlight as the source of energy. During the process of preparing food from sunlight by using photosynthesis, carbon dioxide and water, plants produce oxygen, the single most important gas for human and other animal’s existence on the planet. The chemical reaction that is the main part of the photosynthesis process is:

CO2

+ H2O + energy  (CH2O)n

+ O2

The most interesting part of the equation is that moving from left to right, the equation gives the photosynthesis that puts energy into organic molecules for storage, whereas moving from right to left, the equation gives the respiration of animals, which is used to extract useful energy from organic molecules. The former takes place in chloroplasts whereas the later in mitochondria (Eaton-Rye, Tripathy and Sharkey). Photosynthesis rate depends on three main factors including the intensity of light, temperature and concentration of CO2. The chlorophyll pigment mostly participates in the photosynthesis process, which is green and hence reflect the green wavelength of incident sunlight. On the other hand, other pigments reflect other wavelengths and absorb some but never do photosynthesis. The energy gained by these pigments are pass on to chlorophyll and helped the plants in gaining more energy.

Objective

            The main objective of this laboratory experiment is to measure the formation of the waste product, O2, in a photosynthesis process by using a metabolism chamber filled with gas sensors. It will determine the effect of light intensity and light color on the photosynthesis rate of plants.

Equipment

- Light source

- Color filters (Plastic)

- Metabolic chamber with gas sensors

Methods

            The metabolic gas chamber houses both carbon dioxide and oxygen sensors, which can detect and determine any change in the concentration of the gases within the chambers in the presence of plant specimen. A computer interface comes in the form of a hub with the chamber that allows real-time monitoring of the oxygen level through the computer screen. The oxygen sensor determines the amount of oxygen present by constantly measuring the concentration through lead anode, gold cathode and electrolytic solution that is responsible for carrying current, which is generated in proportion with the concentration of the oxygen present. On the other hand, the carbon dioxide sensor makes use of infrared to measure the concentration of the gas. It emits infrared from one end of the tube and measures it at the other end of the tube. The concentration of the carbon dioxide is inversely proportional to the infrared light received at the other end of the tube because it gets absorbed by the carbon dioxide.

The experiment consists of three major parts. First part involves measuring the concentration of oxygen and carbon dioxide in ppt and ppm unit while the leaf is placed in the dark. This will give the actual rate of respiration because photosynthesis cannot happen in the dark. Second part involves repeating the same procedure in the light; the concentration of oxygen or carbon dioxide will account for the combined effect of respiration and the photosynthesis. Subtracting the first part values from the second part values will give the true rate of photosynthesis. In the third part, the same procedures will be repeated for different lights like green, blue and red and measure the result to determine the effect of wavelength on the results.

Discussion

The rate of photosynthesis depends largely on the light intensity and wavelength. The higher the light intensity the more is the photosynthesis as supported by the scale. Secondly, the wavelength of light plays a major role in determining the photosynthesis as can be seen from the data. The lower the wavelength the more is photosynthesis and the opposite is true for lower wavelengths.

From the experimental data, it becomes apparent that the visible light contributes more to the photosynthesis process than the non-visible light. Visible lights are those which the plant leaves reflect off since they already possess the wavelength. For this the tree leaves look like green and less of other color and the green color contribute the largest to the photosynthesis.  On the other hand, the non-visible colors are those which the plant leaves absorb due to unavailability and hence they contribute less to the photosynthesis.

Works Cited

Eaton-Rye, Julian J., Baishnab C. Tripathy and Thomas D. Sharkey. Photosynthesis: Plastid Biology, Energy Conversion and Carbon Assimilation. Springer Science & Business Media, 2011. Print.

Hall, David O. and Krishna Rao. Photosynthesis. Cambridge University Press, 1999.