Process of Photosynthesis and Leaf Anatomy, Wavelengths of the Light Absorbed by the Pigments Found in the Leaves - Lab Report Example

Photosynthesis Name: Unit: Course: Supervisor: Date of submission: Introduction Photosynthesis is the process that occurs in plants and some algae in which the cells that contain chlorophyll convert the light energy from the sun into chemical energy (ATP) and carbohydrates. In the process oxygen is released into the environment (Bryant & Frigaard, 2006). Photosynthesis produces oxygen as one of the key by-products; it thus maintains the required levels f oxygen in the atmosphere and in the water which is used by the organism inhabiting the land surface and water. The chemical process of photosynthesis is that carbon dioxide has both the carbon and oxygen atoms which are used in the synthesis of carbohydrate (Whitemarsh & Govindjee, 1995). The photosynthesis entail combination of the carbon dioxide and water in the presence of light and the green matter (chlorophyll) in order to produce carbohydrate, water and oxygen. 6CO2 +6H2O---sunlight------------> C6H12O6+6O2 Objectives The process of photosynthesis takes place in two important phases which include the light reaction and the Calvin Cycle. The aim of this experiment is to investigate the process of phtosynthesis.The objectives of the experiment are: 1. Through the process of chromatography carry out separation and identify the different pigments found in the leaves. 2. To detach the pigments and establish the wavelengths of the light that is absorbed by the different pigments. 3. To study the relationship that exists between the anatomy of the leaf and the process of photosynthesis. 4. To investigate the adaptations of the leaves for the process of the photosynthesis in varying environments. Experiment The process of the experiment was divided into two, exercise A and exercise B. Exercise A Exercise A entailed the use of organic solvents for the separation. The following steps were followed in the experiment: 1. A 5ml solvent of acetone-petroleum 10:90 ether was poured into chromatography jar after which the lid was replaced. The jar was filled with the solvent vapour. 2. Leaf materials weighing 2g were cut and ground with morta and pestle. 3. The materials were put in a test tube and 4ml of acetone was added after which the test tube was tightly closed and shaken, it was then left to stand for duration of ten minutes. 4. After the 10 minutes 3ml of water were added and shaking was again done carefully. The water soluble pigments dissolved in water, the water turned green. 5. The solution was further added 3ml of petroleum ether and the process of shaking was repeated, the solution was let to stand for several minutes until the pigments separated into different layers. The upper layer was dark green. 6. Using the Pasteur Pipette, the dark green layer at the top was removed and placed in a beaker. 7. Using the capillary tube, a small drop of the extracted pigment was placed in chromatography paper strip. This was allowed to dry before another small drop was added to the same spot; the process was repeated for six times. 8. The paper strip was then lowered into chromatography jar to the extent that the tip of the paper touched the solvent; this was done carefully ensuring that the paper strip did not touch the sides of the jar. 9. The chromatography jar was then left for sometime and observations were made at frequent intervals. 10. Before the solvent reached the top of the paper, the paper was removed from the jar. 11. The paper was allowed time to dry (some minutes). 12. Observations were made for the different colours. For further analysis, each pigment band from the strips of the papers were cut and each band was put into different beakers each with small quantities of acetone. This led to the pigments being eluted. The pigment acetone was then transferred into cuvette each separately. This was then set into spectrophotometer in which the absorbance of the pigments was measured at intervals of 10nm. Exercise B. A prepared slide of a dicot leaf was obtained and examined using the compound microscope. Using the lower power, the overall impression of the anatomy was obtained. Details of the orientation of the leaf veins were noted. The examination located the midvein within the midrib. Using the high power, the examination of the blade of the leaf blade in the one side of the midvein was carried out and a diagram for the observations were made. Results of Exercise A Through the chromatography, four colours were observed; they included chrome yellow (carotene), greenish yellow (xanthophyll), bluish green (chlorophyll a) and yellowish green (chlorophyll b). On the further analysis of the pigment band and absorption in the spectrophotometer, it was found that the absorption varied depending on the wavelength. The absorption increases as the wavelength increases from 380nm to 480nm. After the absorption drops at wavelength of 490 nm, it assumes a plateau and the absorption starts increasing at 630nm. Results of exercise B Discussion In the process of photosynthesis, there are several pigments that are acted upon by the light energy in order to produce the carbohydrate and the by-products of water and oxygen. According to Rabinowitch and Govindjee (1965) core to the photosynthesis process is the different shades of chlorophylls which include a, b, c and d. All the green plants have chlorophyll which is the pigment largely responsible for the synthesis. The chlorophyll absorbs both the red and blue light strongly than the other chlorophylls. Plants have at least two chlorophylls a and b. The chlorophylls are normally arranged in photosystems which are normally found in the thykaloid membranes of chloroplasts. These chlorophylls main function includes the absorption of light which is then transferred to the centres of reaction in the. The absorption peak from the chlorophylls is normally at 665 nm and 450 nm. In a leaf, the chlorophyll co-exist with other pigments which also absorb light, these other pigments absorb the light from the different wavelengths which the chlorophyll cannot absorb (Gates, Keegan, Schleter & Weidner, 1999). The pigments include the carotene and xanthophyll. The xanthophyll can absorb light best at 400-530 nm. These pigments are involved in photosynthesis with chlorophyll, however chlorophyll is abundant than these pigments and this is the reason for the green colour of the leaves. The chloroplasts are found on the upper part of the leaf. The chloroplasts have the different molecules of pigments which are used for photosynthesis, especially the chlorophyll, the leaf is thus adapted to environment in a way that the chloroplasts is on the upper part facing the sunlight. This makes it easy for the light to strike the pigments for the process of photosynthesis to take place (Mullineaux, 1999). Diagram 1: Adaptation of leaf (Mullineaux, 1999) In relation to the light, the eucalyptus leaf was relatively thin and few stoma mainly lower part of the leaf and the cuticle was waxy while the typical dicot leaf is broad. The reason behind the varying anatomical features was the adaptability to different climatic conditions. The thinness and waxy cuticle allows the eucalyptus to lose water through evaporation by reducing exposure to sunlight (Mansanares, Barja, Silva & Alves, 2001) Possible sources of error In the experiments, there are possible of errors that could be encountered. In exercise A, the possible source of error could be grinding the 2g of leaf instead of pounding. This could interfere with the pigments. The other source could be failure to let the pigments dry completely in the chromatography paper, addition of another drop before the first dries could affect the colour separation. Improvements The errors could be avoided by ensuring that proper timing is used in the process of using the Pasteur pipettes to drops the pigments to the paper chromatography. Pre-trials can be carried to establish the time intervals for drying which can be used in the real experiment. Conclusion Photosynthesis is an essential process for living organisms, the food requirements for the living organisms are normally achieved from the process either directly or indirectly from the plants through the support of the light energy. The leaf of a plant normally has chloroplasts which contain molecules of different pigments. These pigments are responsible for the process of photosynthesis as they utilise the light from the sun to breakdown the carbon dioxide in presence of water molecule to form carbohydrates and produce oxygen. The main pigment responsible for the photosynthesis is chlorophyll. Plant leaves are adapted to different environmental conditions which enable them to utilise the minimal light wavelength to carry on the process of photosynthesis, by ensuring that most of the chloroplasts are located in the source of sunlight. References Bryant, D. A. and Frigaard, N. U. (2006). Prokaryotic photosynthesis and phototrophy illuminated. Trends Microbial, 14 (11), pp. 488–96. Doi: 10.1016/j.tim.2006.09.001. PMID 16997562. Gates, D., Keegan, H., Schleter, J. and Weidner, R. (1999). Spectral Properties of Plants," Applied Optics, 4(1), pp. 11-20. http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-4-1-11 Mansanares, M.A., Barja, P.R., Silva, E.C. and Alves, P.L. (2001). Photosynthesis in Eucalyptus Studied by the Open Photoacoustic Technique: Effects of Irradiance and Temperature Acoustical Physics, 47(1), pp. 16–21. http://www.researchgate.net/publication/225541926_Photosynthesis_in_eucalyptus_studied_by_the_Open_Photoacoustic_technique_Effects_of_irradiance_and_temperature/file/9fcfd5065922f09625.pdf Mullineaux C. W. (1999). The thylakoid membranes of cyanobacteria: structure, dynamics and function. Australian Journal of Plant Physiology, 26 (7), pp. 651–689. Doi: 10.1071/PP9902 Whitemarsh, J. and Govindjee, (1995). The photosynthesis process: Concepts in photobiology. Journal of Applied Physics, 13 (1), pp. 513-532. http://www.life.iilinois.edu/govindjee/paper/gov.html Rabinowitch, E. and Govindjee (1965). The role of Chlorophyll in Photosynthesis. Journal of Applied Physics, 1(1) http://www.life.ollinois.edu/govindjee/Electronic%20Publications/1965/1965_ Rabinowitch_Gov.pdf Read More