Photosynthesis and Photosynthetic Pigments The main components of living plant cells - polysaccharides of the cell wall, proteins and nucleic acids, and fats are made from sugars and mineral elements in very small but important quantities. Sugar provides the carbon, hydrogen and oxygen that make up the protoplasm and cell walls. For every sugar molecule converted into this material, another molecule is respired to become CO2and H2O to obtain energy, in the form of energy-rich phosphate bonds or hydrogen, necessary for synthesis in cells. The suggestion that plants get some of their "food" from the air through the leaves is shown in the book "Vegetable staticks" written by Stephen Hales and published in 1727. He wrote: "It is very likely that plants get, through the leaves, some of their food from the air ”. It was not until about 1864 that quantitative measurements of gas exchange allowed statements about the overall reaction of photosynthesis to be made: 6 CO2+ 6 H2O ----→ C6H12O6+ 6O2 In this overall reaction approximately 691,000 calories of light energy are absorbed and converted to free energy in hexose. In order for the absorption of light energy to take place, photosynthetic pigments are needed, especially chlorophyll which is found in plants. The photochemical phase of photosynthesis includes two photosystems, namely photosystem I which is rich in chlorophyll a and contains carotenoids and less chlorophyll b than Photosystem II. In both photosystems, the pigments generally act to harvest light energy and transfer it to chlorophyll a which is located in the reactive center of the photosystem. This energy will later be used to reduce water molecules (in the light reaction of photosynthesis), with the help of Cl ions-and Mn2+; H2O -----→ 2H++ ½ O2+ energy Next is energy and H+will be used in the formation of ATP and NADPH which provide energy and reducers for CO fixation2during the dark reaction of photosynthesis, while O2released into the environment. It is generally known that the process of CO2water and light energy become hexoses consist of a series of integrated reactions. The fact that this process requires light means that in some step of the photosynthesis process light must be involved. If the speed of this step is reduced due to low light intensity this step will affect all other steps and therefore determine the overall speed of photosynthesis, which can be measured from O2released or CO2which is absorbed. Light becomes a limiting factor in photosynthesis at low light intensity, so the overall process speed is determined by the speed of light energy supply. Above a certain light intensity, further addition of light has no effect on oxygen release. The process is said to become light saturated. Furthermore, it is found that if light is not a limiting factor, the speed of photosynthesis is responsive to changes in temperature, which is because photosynthesis reactions are chemical reactions, which are sensitive to temperature. The internal plant factor that plays the most role in this energy conversion is the green pigment called chlorophyll. Chlorophyll is a very important photoreceptor in plants which plays a very important role in the process of photosynthesis. Chlorophyll is insoluble in water but soluble in ethanol, methanol, ether, acetone, benzol and chloroform. Basic principles of spectrophotometers in measuring chlorophyll levels If we look at a solution of a colored substance, the more concentrated the solution, the more it absorbs light so it looks darker. The existence of a relationship between light absorption and solution concentration is the basic principle of using a spectrophotometer. This tool uses monochromatic light. A bottle containing only solvent without the solute is placed in a beam of light. The strength or intensity of light passing through the bottle can be measured with a photocell, determined as 100% transmission. If it is replaced with a colored solution, some of the light will be absorbed so that the recording by the photocell will be lower. This relationship can be expressed in the equation where: I0= light passing through the solvent only Is= light passing through the solution T = transmittance, as the light that can be passed through the solution. Usually expressed in percent (%). Determining concentration in this way is easier because OD is linearly related to concentration, which can be written with the formula: A = k . b. c Where k = constant b = thickness of solution through which light passes c = concentration The results of OD measurements of various concentrations can be depicted in the following graph: Photosynthetic pigment paper chomatography Chromatography is a technique for separating the constituent components of a mixture, such as photosynthetic pigments found in plant leaves. The separation of these components is based on the difference in molecular weight between the constituent components so that there will be a difference in the flow velocity of the components in a substance (eluent) which will bring the components to move (moving phase) in a medium that does not move (stationary phase). In paper chromatography, the stationary phase uses paper media as a place for the separation process to take place. Photosynthetic pigments consisting of chlorophyll a and b, betacarotene and xanthophyll have different molecular weights so that using paper chromatography techniques we can see the differences between each of these components in making up the color pigments in the leaves. The main principle of paper chromatography on photosynthetic pigment components is that the larger they are Concentration the size of the pigment molecule or the heavier the pigment molecule, the slower its movement will be when it passes through the moving phase on the paper medium (stationary phase).