The Role Pigments Play in Photosynthesis and Other Plant Functions and Structure of a Leaf - Lab Report Example

PHOTOSYNTHESIS Name of Student Name of Institution Name of Professor Date of Submission Table of contents 1 Executive summary………………………………………………………………..iii 2 Introduction…………………………………………………………………………4 3 Aim and Objectives……………………………………………………………….…4 4 Materials and Methods……………………………………………………………….5 5 Results and discussions……………………………………………….……………...6 6 Table 1…………………………….………………………………………………….9 7.0 Diagrams of leaf anatomy …………………………………………………………..10 8.0 Discussion..........................................................................................................…......11 9.0 References……………………………………………………………………………13 Executive summary The process of photosynthesis is quite significant to plant life. This research report has highlighted the biochemical and biophysical features of photosynthesis in plants using experiments on eucalyptus leaf and a typical dicot leaf. Paper chromatography has been applied in separation of the chlorophyll pigments and spectra analysis applied in determining the absorption of individual pigments. Two leaf materials have been used to analyze structural compositions and differences. The paper indicates that various chlorophyll pigments absorb energy at different wavelengths. It also indicates that structural properties of leaves are quite significant in determining the activities within the leaves. Introduction Photosynthesis is without a doubt one of the most significant yet complex processes in the world. While a process involving the light-to-chemical energy conversion and storage of the energy in sugar bonds, photosynthesis takes place in plants, particular algae from the protista kingdom and cyanobacteria (commonly termed as the blue algae) from kingdom monera. In order to occur and manufacture sugar (Adenosine Tri-phosphate), photosynthesis often requires light energy, carbondioxide (CO2) and water (H2O). The involved chemical; reaction leading to the manufacture of the sugar can best be illustrated by the equation 6 CO2 + 12 H2O (+ light energy) → C6H12O6 + 6 O2 + 6 H2O. While issues relating to photosynthesis could be quite complex and elaborate, this particular paper seeks to align itself to experiments conducted on leaf samples.. Aim and Objectives The aim of the experiment is using spectrophotometer in analyzing samples based on their light absorption. The data from the samples will offer an opportunity of comparing the various pigments within the leaves Objectives: The main objectives of the lab exercise are: To understand the role that pigments play in photosynthesis as well as other plant functions To understand paper chromatography and its basic principles To understand the basic structure of a leaf and its relationship with environmental adaptation To apply the results generated from the pigment exercise in generating lab report, an activity that is quite significant in improving the writing skills and the ability of conveying information in an accurate, precise and systematic manner. Materials and Methods The main focus of exercise 1 relates to paper chromatography. In this particular exercise, 5ml of acetone-petroleum ether 10:90, grounded leaf material, chromatography jar, water, pipette, capillary tube and paper strip are used in determining pigmentation. 5ml of the acetone-petroleum ether is poured into the chromatography jar from which 4ml is added to the material grinded leaf material in the in the test tube and shaken thoroughly. This is left to stand for 10 minutes after which 3ml of water is added and consequently another 3ml of the acetone-petroleum ether is added. It is shaken and left to stand for some minutes until the pigments are separated into layers. The upper solvent layer is removed by pipette and placed into a beaker, and droplets of the pigment extract are applied to the chromatography paper strip, about a centimeter from the strip’s end. It is done consecutively 6 times with application made each time the paper dries. For spectra analysis, elution of pigments is conducted by cutting out the different pigment bands and placing each of the bands in a different beaker containing acetone. After elution, each pigment acetone solution is placed in a different curvette from which spectrophotometer is used to measure absorbance of pigments at 10nm intervals within the range of 380nm to 700nm In exercise 2, the experiment explores the leaf structure and functions. In examining this, leaf morphology and leaf anatomy are given due focus. To determine leaf morphology, the particular leaf is put on display whereby its visible characteristics are analyzed including the number of leaf blades it has in a single petiole. On the other hand, leaf anatomy is conducted on by obtaining a slide of a typical dicot leaf which is later examined under a microscope. Low power lens is used to get an overall view of the anatomy, including phloem, midrib and midvein. The high power lens (*40) is used to study a portion of the leaf to locate and describe aspects within it including the cuticle, spongy mesophyll and epidermis. The procedure also applies to the eucalyptus leaf, Results and discussions Results In the first experiment, the solvent runs on the paper strip and the different chloroplast pigments become evident where they are separated in form of distinct spots on the paper strip. After drying, the various pigments become visible and their varying colours become evidently clear for identification. The pigments include carotene which is chrome yellow in color, xanthophyll which is greenish-yellow in color, chlorophyll-a which is bluish-green and chlorophyll-b which is yellowish green in color. When the different pigment bands are cut and dipped in individual beakers containing acetone, elution occurs and the solutions retain the pigments. By placing the solutions in different curvettes and examining them using a spectrophotometer within the wavelength range of 380-700 nm, varied wavelengths are detected thereby indicating varied absorption trends. Absorption spectra According to the spectrophotometer readings, chlorophyll –a has its absorption peak ranging between 650nm and 430nm while Chlorophyll-b has its absorption peak between 640nm and 450nm. Xanthophyll absorb best at 480nm and 450nm while carotene peaks at 450nm and 420nm As illustratd in table 1, all the pigments have varying absorpition peaks. In chlorophyl a, there are gradual increments in the absorption within the range of 380nm to 430nm where. The absorption gradually increases from 0.380 to 0.824. after the 430nm mak, howevever, there is a significant decline in the absorption, a trend that persits until the 560nm mark is reached where the gradual increments lead to the peak at 650nm. This is the highest peak in chlorophul a. chlorophyl b begins experiencing gradual absorption increments at 400nm (0.055) though to the peak of 450nm where it maintins a constant decline until 530nm. The absorption at this point is 0.015, which gradually gains considerable incremental adjustments to 640nm(0.065). xanthophyl presents a rather different scenerio,. While it peaks at 430nm(0.013) and maintains incrased absorption to this level, its absorption development is not uniform after e 430nm regardles of the final peak being at 480nm.carotene is another pigment with unique absorption characteristic. At 380nm, carotene maintains constant increases in absorption to the peak of 420nm ( 0.095). after which the absorption varies to the peak of 450nm. In the stiudy of leaf structure and properties, it was quite evident that the palisade layer located near the surface of the leaf has many chloroplasts. On the contrary, the lower epidermis has several pores. It is also quite clear that both the typical dicot leaf and the eucalypt leaf have structural differences and similarities. Both of the leaves have the basic parts including the epidermis, phloem, and cuticle. However, there is a sharp contrast between the two with regards to gland and spongy cells. Whereas the eucalypt leaf hardly shows any spongy cells in it, it has an oil gland. On the contrary, the typical dicot leaf has spongy cells but no oil gland. Table 1. Absorbance of light by plant pigments. Group 2 (Afternoon) – Table 1. Absorbance of light by plant pigments. Wavelength (nm) 380 390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 Carotene 0.052 0.057 0.068 0.080 0.095 0.101 0.111 0.121 0.111 0.099 0.095 0.073 0.039 0.019 0.010 0.007 0.005 0.005 Xanthophyll 0.039 0.059 0.085 0.077 0.089 0.090 0.109 0.113 0.090 0.043 0.096 0.048 0.018 0.009 0.005 0.001 0.001 0.001 Chl. a 0.380 0.395 0.492 0.626 0.651 0.824 0.433 0.166 0.116 0.124 0.086 0.046 0.029 0.024 0.029 0.035 0.034 0.032 Chl. b 0.057 0.050 0.055 0.068 0.092 0.121 0.125 0.197 0.194 0.104 0.043 0.020 0.016 0.014 0.014 0.015 0.016 0.016 Wavelength (nm) 560 570 580 590 600 610 620 630 640 650 660 670 680 690 700 710 720 Carotene 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.004 0.005 0.005 0.005 0.004 0.003 0.003 0.003 Xanthophyll 0.001 0.001 0.001 0.001 0.002 0.002 0.002 0.002 0.002 0.003 0.005 0.005 0.002 0.001 0.001 0.001 0.001 Chl. A 0.042 0.062 0.072 0.063 0.085 0.120 0.123 0.096 0.110 0.888 0.641 0.399 0.083 0.016 0.007 0.004 0.003 Chl. b 0.017 0.018 0.019 0.022 0.022 0.021 0.020 0.029 0.065 0.065 0.037 0.019 0.008 0.005 0.004 0.003 0.005 Anatomy of the leaf samples Discussion Explanation of Results While the paper chromatography indicated distinct colours, the green colour was quite visible due to the green light being reflected rather than absorbed, a fact that has been similarly highlighted by Moss & Loomis (1952) . The absorption spectra exhibited varied absorption trends by the four pigments, with the range being between 650nm and 420nm. The molecules of chlorophyl pigments absorb light wavelength between 700nm-400nm (also refered to as the photosunthetically-active radiation). Carter & Knapp, (2001) similarly state that the visible wavelengths range between 400-720 nm. The analysis also indicates that every pigment in the chlorophyl has a certain level of energy it can sense or absorb. the absorption differences exhibited by the absorption spectra is attrubuted to the fact that while the pigments are presented with varied wavelengths, they can only absorb the specific energy levels capable of raising their orbital electron to the excited/quantum state. Higher energy levels tear the pigment molecules apart or cause bleaching and death (Müller , Li & Niyogi, 2001) while lower energy levels can not raise the orbital electron to the quantum state for initiating the photosynthesis process. The absorption of light relates to electron excitation states Regarding the anatomical structure of leaves, the upper part of the leaf, and specifically the palisade layer, had several chloroplasts which serve a critical role of increasing lightenergy absorption. the palisade layer has several chloroplasts to enable the leaf optimize on the absorption of energy from light since photosynthesis is light dependent. According to Evans (1999), the palisade tissue that is located nearest to the surface and which receives the light, actually facilitates light penetration. The lower epidermis has several pores which serve the role of exchanging substances, especially gases, from the leaves. A notable contrast in the leaf structures is the presence of oil gland in the eucalyptus leaf and the absence of it in the dicot leaf. Eucalyptus trees leaves have oil glands that serve to secret essential oils that, according to Morrow & Fox (1980), serve to defend eucalyptus from attacks by repelling herbivores and some insects. Dicot leaves have spongy cells and palisade mesophyll. Evans (1999) additionally indicates that spongy mesophyll serves a significant role of promoting scattering in order to enhance the process of light absorption. In conclusion, it is evident that plant leaves have various pigments within them, pigments that enable the photosynthesis process to take place. The leaf structures are also quite varied. The results are largey consistent with literarure. apart from the experimental research conducted on the terrestrial plant leaves, it is imperative for future experimental research activities should involve the study of the leaves from aquatic plants. References Carter, G. & Knapp, A., 2001, “Leaf optical properties in higher plants: linking spectral characteristics to stress and chlorophyll concentration” American Journal of Botany, vol. 88 no. 4 677-684 Evans, J., 1999, “Leaf anatomy enables more equal access to light and CO2 between chloroplasts” New Phytologist, Volume 143, Issue 1, Pp 93–104 Müller , P, Li, X. & Niyogi, K., 2001, “Non-Photochemical Quenching. A Response to Excess Light Energy”Plant Physiology, vol. 125 no. 4 1558-1566 Morrow, P. & Fox. L., 1980, “Effects of variation in eucalyptus essential oil yield on insect growth and grazing damage”, Oecologia,Vol 45, Pp. 209-219 Moss, R. & Loomis,W., 1952, “Absorption Spectra of Leaves. I. The Visible Spectrum” Plant Physiology 27(2): 370–391. Read More