Effects of Light Wavelength on Photosynthesis - Lab Report Example

Nhung Nguyen Effects of Light Wavelength on Photosynthesis Dracaena plants were used in an experiment to study the effect of different sources of light with particular wavelengths on the photosynthetic process by evaluating the amount of CO2 consumed. Appropriate filters were used to obtain wavelengths of 630 to 750 nm representing red, 570 to 590 nm representing yellow, and 490 to 560 nm representing green light. A control experiment was conducted in direct sunlight. However the experiment failed to elicit any variations in photosynthesis, as measured by CO2 consumption with the red, yellow and green light sources as expected. The experiment with white light showed significantly higher rate of photosynthesis as compared with individual wavelengths. Introduction The plant kingdom is unique in all life forms on this planet due to the ability to synthesize its own food from the environment. The presence of a unique green pigment, chlorophyll in the plants enables them to utilize the environmental CO2 and other components, in the presence of light to manufacture food in the form of starch. The presence of solar light is absolutely essential for photosynthesis to occur, as the name itself suggests. It has been seen and experimentally proven that plants cannot survive in the absence of light. Light is basically an electromagnetic radiation and white light is a blend of many wavelengths, composed of seven colors. Particular wavelengths of light may be more pertinent to photosynthesis and this fact has been investigated up to a great extent. Both light quantity and light quality are important aspects affecting photosynthesis which have been extensively investigated (Figueroa et al, 1995). Light is such an important factor that it exerts its actions on plant morphology itself, in terms of shape, size and orientation of the plant and its effects extend to the vegetative development and reproductive induction in plants (Figueroa et al, 1995). Changes in light frequency and intensity influence physiological events in plants. Numerous studies have been done on the influence of different wavelengths of light on stomatal opening and conductance (Zeiger & Field, 1982), changes in the photosynthetic apparatus (Walters & Horton, 1994) and leaf characteristics (Gulmon & Chu, 1981). It is therefore interesting to find out what effects, different light sources will have on the photosynthetic process which is the objective of this experiment. This experiment examined the hypothesis that photosynthesis would be affected by the wavelength of light received by the plant. It was predicted that the red light (630-750nm) would allow the greatest amount of photosynthesis. Methods The impact of light wavelengths on photosynthesis was determined by exposing the plant Dracaena to light of different wavelengths and then measuring the decrease in carbon dioxide level of the chamber, which indirectly indicated the amount of photosynthetic activity. Red, green and yellow light filters were placed in front of a 60 Watts soft white light bulb creating wavelengths of 630 to 750 nm representing red, 570 to 590 nm representing yellow, and 490 to 560 nm representing green. Plants were exposed exclusively to these frequencies of light in individual experiments with sunlight treatment in the green house serving as control. All exposures were made at normal room temperature. Each of seven plants were placed in the CO2 analyzer and tested for initial CO2 level. In each experiment the drop in CO2 level after two minutes of light exposure was noted and final measurements were obtained after seven minutes of exposure. Results Changes in CO2 utilization did not show significant changes at different wavelengths. Figure 1. Change in CO2 as a result of exposure to red, green, yellow and sunlight. Means ± 95% CI. The experiment did not reveal any changes in CO2 consumption when plants were exposed to exclusively red, yellow and green light. However, in the experiment where direct sunlight (white light) containing the total spectrum was used, a significant change in the utilization of CO2 was noticed, which was much more than that of exclusive spectrums of red, yellow and green used alone. Discussion The results acquired were not consistent with our hypothesis that photosynthesis would be affected by the wavelength of light received. The experimental design can be blamed for this anomaly as similar standardization procedures were not adopted for the experiments. The environmental temperature, watering of the plants and other available nutrients has to be standardized for such experiments (Zeiger & Field, 1982). In their experiment, Zeiger & Field (1982) had used Malva parviflora plants for such experimentation which were germinated, transplanted and grown in identical environmental and nutritional situations before conducting the experiment. Other factors such as leaf temperature, focusing of particular frequency of light using specialized equipment and the exposure time have to be done using sophisticated and established techniques. In their experiment, Zeiger & Field (1982) were able to demonstrate a higher photosynthetic rate when various intensities of red light were used, as compared to white light alone. The location of the photoreceptors on the leaf surface also has an influence on photosynthesis as was demonstrated in an experiment by Sharkey & Raschke (1981) where they discovered that blue light (430-460 nm) was 10 times more effective in producing stomatal conductance as compared to red light (630-680 nm). Green light was found to be virtually ineffective in their experiment. There is a functional coupling between photosynthesis and stomatal conductance as was shown by Zeiger & Field (1982). They showed that both photosynthetic quantum and rate was higher under red light as compared to blue. However they found that blue light at low intensity of radiation had more effect on increasing stomatal conductance. Red light increases net photosynthesis without affecting stomatal conductance once the leaf has had prior exposure to low intensities of blue light. The intensity of light also causes changes in the composition of the photosynthetic apparatus (Walters & Horton, 1994). In their experiment, the authors found that “plants grown under four different light regimes showed differences in development, morphology, photosynthetic performance and in the composition of the photosynthetic apparatus”. They observed variations in response to high, low as well as light with different spectral qualities. Experiments which are able to discern the differences due to spectral changes in wavelength of light on photosynthesis are therefore dependent on multifarious factors which involve methodologies to provide strict standardizations along with the use of sophisticated analytical tools. Our experiment therefore could not detect the differences when exposure to particular frequencies of light was given, but it gave a significant difference in the experiment conducted in sunlight, which shows that other factors had contributed more to the photosynthetic process in our experiment than the light source alone. Work Cited Figueroa F. L., Aguilera J. and Niell F. X., (1995), Red and blue light regulation of growth and photosynthetic metabolism in Porphyra umbilicalis (Bangiales, Rhodophyta), Eur. J. Phycol., 30: 11-18 Gulmon S. L. & Chu C. C., (1981), The Effects of Light and Nitrogen on Photosynthesis, Leaf Characteristics, and Dry Matter Allocation in the Chaparral Shrub, Diplacus aurantiacus, Oecologia (Berl) 49:207- 212 Sharkey Thomas D. & Raschke Klaus, (1981), Effect of Light Quality on Stomatal Opening in Leaves of Xanthium strumarium L., Plant Physiol. 68, 1170-1174 Walters Robin G. & Horton Peter, (1994), Acclimation of Arabidopsis thaliana to the light environment: Changes in composition of the photosynthetic apparatus, Planta 195:248-256 Zeiger Eduardo and Field Christopher, (1982), Photocontrol of the Functional Coupling between Photosynthesis and Stomatal Conductance in the Intact Leaf BLUE LIGHT AND PAR- DEPENDENT PHOTOSYSTEMS IN GUARD CELLS, Plant Physiol. 70, 370-375 Red light Start end difference 780 754 26 536 519 17 443 428 15 953 938 15 823 788 35 864 838 26 783 754 29 Green light Start end difference 487 455 32 459 441 18 500 484 16 555 531 24 1099 1082 17 327 316 11 501 477 24 Yellow light Start end difference 557 532 25 422 407 15 509 479 30 568 538 30 568 538 30 440 408 32 529 512 17 Sun light Start end difference 670 582 88 359 281 78 660 517 143 378 217 161 852 633 219 773 589 184 1226 994 232 Red light Green light Yellow light Sun light Variance 60.2 47.6 47.6 3567.8 SD 7.76 6.9 6.9 59.7 SE 2.93 2.61 2.61 22.6 95% interval 7.18 6.38 6.38 55.2 Means Red 23.3 Green 20.3 Yellow 25.6 Sun light 157.9 Read More