The term “photosynthesis” is so called because it synthetic process driven by light. Many studies have been carried on the light spectrum quality, intensity, wavelength and their combinations thereof on the rates of photosynthesis. Different importances have been attributed to different factors. But light and carbon dioxide are the most important paramers for active photosynthesis. In the present studied effect of light intensities (low and high) were investigated. It was found that Light is crucial for photosynthesis.
It was also shown that Red and blue colors were also involved for this process but not as good as both put together in the form of the total light spectrum. Introduction Respiration is a biochemical process, a characteristic of all living organisms and takes place in living cells. Photosynthesis is also a biochemical process which is found in plants with green leaves and other organs exposed to light . All biochemical processes are regulated by enzymes. Enzyme activities are catalyzed and regulated by temperature and light. All biochemical processes are regulated by enzymes.
Enzyme activities are catalyzed and regulated by temperature and light. In both the processes energy levels change. In respiration carbohydrate is converted into CO2 and water accompanied with the liberation of energy (conververting ATP into ADP). In photosynthesis a reverse of this reaction takes place with the fixation of atmospheric CO2 into glucose and O2 from water is released back into the atmosphere. In this process energy biomolecules (called ATP) are produced. In both the situations. There is a transfer of electron from a donor to a receptor in a chain called as the Electron transport Chain.
In photosynthesis, light was source for energy fixed into a carbohydrate (Arnon, 1961), while in respiration carbohydrate was the primary donor( Materials and Methods Light Intensity and photosynthesis Six tubes of algal cultures were obtained. To each of them 4-5 drops of 1%phenol red was added. Phenol Red is a pH indicator, red in acidic and yellow in acidic solution. Into three tubes air was gently blown with the help of a straw with the other end in the solution. Time taken for color change in each was recorded. Three BOD bottles containing algal cultures were kept in three different light conditions-
dark, low light (20W), and high light (100W) for one hour. In the fourth bottle, initial oxygen concentration was measured at the start of the experiment using the Winkler’s method. The same method was used for the other three bottles after one hour. Winkler Titration Method: (Grasshoff, 1983) To each of the above four bottles 0. 5 ml MnSO4 reagent and 0. 5 mL alkaline iodide azide reagent were added. The bottles waere carefully stoppered without letting any air bubbles inside and mixed by inverting them carefully without spluttering of the liquid outside.
Care was taken to see that the liquid does not fall on the body. The bottles were rested to allow the floc to settle to 1/3 of the level. The bottles were gently mixed again. To each bottle 0. 5 ml of conc. H2SO4 was added at the base of the floc. In handling the conc. H2SO4 labcoat, goggles and gloves were put on as precaution The bottles were mixed again. The contents were taken into 250 ml Erlenmeyer flasks. Since the volume of the BOD bottle is 60 mL and since 1. 5 mL was displaced with reagents, volume of sample was 58. 5 mL of sample.
A burette was filled with 0. 125 N sodium thiosulfate (Na2S203). The samples were titrated until a very pale yellow (“straw”) color appeared. The solution were mixed while titrating by swirling. Two drops of starch indicator solution were added and the solution mixed to get a uniform blue color. Titration was done carefully until the first disappearance of color and without crossing the endpont. The blue color should return on standing in 10 to 15 seconds. Volume of titrant (mL) used was recorded. . One mL of 0. 0125 N Na2S203 is equivalent to 0.
1 mg DO, To calculate oxygen concentration (mg/L), multiply volume of titrant used by 1. 71 [0. 585 mL titrant = 1 mg O2/L in 58. 5 mL sample; 1/0. 585 = 1. 71] Under alkaline conditions, dissolved oxygen oxidizes divalent manganese to a trivalent state. When the solution is acidified, trivalent manganese hydroxide reacts with added iodide forming free iodine. The iodine liberated is stoichiometrically equivalent to dissolved oxygen. The amount of iodine is then determined by titration with a thiosulfate solution of known concentration. Light Independent reaction – Photyosynthesis
A leaf of the Coleus plant on the bench that contains a few colours was collected. A piece of white paper over leaf, and using a window the outline of the pattern of colors were traces. Each section was labeled with its colour. A boiling alcohol bath was set up. A 400mL beaker containing approximately 150mL of water was placed on a hot plate. Then a 250mL beaker containing approximately 100mL of ethanol was placed in the beaker containing water. This boiling alcohol bath was used The coleus leaf was placed into hot alcohol. When the leaf is almost white, it was
removed from the hot alcohol and placed in a Petri dish. Iodine was pored over it. Starch stained blue-black. The starch-containing areas were marked on leaf tracing. Results were recorded as in Table Wavelengths and Photosynthesis Different light filters were attached to plant leaves for two weeks permitting exposure to only to specific wavelengths. A leaf with a light filter and leaf with no filter were selected. Each leaf was placed into the boiling alcohol bath, until the leaf is almost white. both leaves were not put into the bath at one time.
A record was made as to which leaf came from which light treatment. The leaf was carefully removed from alcohol; washed thoroughly and placed into a Petri dish. Iodine was poured over it. They were observed for the presence of starch. Results were recorded as in Table 3. 4. The leaves exposed to five different light treatments were ranked ( 1-5 scale; 1. dark, and 5 none). The colors were compared withose of other students. Demonstration of Electron Transport Chain On the side bench two beakers labelled as #1 and #2 were provided. One beaker
containing corn kernels which have been previously boiled to kill the embryo in the seeds. The other beaker contains live corn kernels. Two glass Petri dishes were labelled #1 and #2. Into each, place several corresponding corn kernels from the beakers on the side bench. The kernels were into right and left halves with razor blade. Several drops of Triphenyl tetrazolium chloride (TTC) in each dish. Kernels were placed with cut side down into the TTC drops. After 30 minutes, and after 1 hour, the Petri plates were lifted up to look beneath. The results were recorded as in Table 3.
5. Results Light Intensity and Photosynthesis Three light regimes were examined for the effect of light intensity on the net rate of photosynthesis in one bottle of algal culture placed in each regime – dark, low light (20W) and high light (100W) for one hour. At the start of the cultures Phenol red indicator solution was used to indicate changes in pH of the culture medium. As was expected, it was found that the net oxygen evolution as measured in this experiment was negligible 0. 715mg/mL, while the bottle in low light showed a significantly amount of oxygen 3. 148.
At higher light (100W) light intensity the oxygen production was more (3. 48) (Table 1). This strongly suggests that light is required for photosynthesis. This further supports the hypothesis that light intensity supports the evolution of oxygen and consumption of CO2. Light Independent Photosynthesis In an experiment variegated leaf of Coleus was used for examining the role of green and non-green regions of the leaf in photosynthesis. It was found that green regions picked up dense blue color due to the presence of starch, while the lighter non -green areas did not pick up any color.
The other yellowish areas picked up some color but not as much as the green areas. This shows that non-green lighter and whitish areas are not active in the dark reaction of photosynthesis. This proves that chlorophyllous areas are active in this process (Table 2 ) Light wavelengths and photosynthesis To examine possible active wavelengths in photosynthetic process, leaves covered with five different colors were checked. It was not unexpected that the dark exposed leaves did not show any color indicating that starch was absent and that photosynthesis did not take place when exposed to darkness (Table 3).
On the contrary leaves exposed to full light spectrum had maximum color sue to the presence of high starch content. Among the other three colors tested green filters showed the highest color followed by blue and green filters. This suggests once again that full light spectrum shows the highest photosynthetic potential. Red and green also the ranges of wavelengths which activate photosynthesis but to different degrees. Both photosynthesis and respiration involve energy level differences. They go through an electron transfer chain. Triphenyl tetrazolium chloride has been often used to prove the viability of seeds.
and pollen due to their ability to respire and produce CO2. This is achain process in which electrons are transferred from one to another carrier. When TTC is used it works as a trap for electrons in the chain and turn carmine red as was seen in our test with maize kernel halves. The dead kernels did not show any change in color. Discussion Photosynthesis and respiration are biochemical processes. Their activities depend upon a number of physical and chemical factors. Both the processes are directly related to carbon metabolism and energy balances in an organism.
Photosynthesis requires the presence of light for the process while respiration does not need light. Photosynthesis is a two step process – the first requiring light as the energy source and second the light independent cycle. In the first one called the light reaction water is split to release oxygen and the H is used enzymatically in the second, or the Dark reaction to convert carbon dioxide into glucose therough a series of enzymatic steps. called Calvin Cycle (Calvin, 1956). Oxygen produced during photosynthesis originate from watr in the presence of light (Hill, 1939).
The present experiments confirm the findings of Arnon (1956). That light is required for photosynthesis. The present experiments also confirm that the blue wavelengths an the red wavelengths are specifically active in the light reaction. It is the energy from light captured by chlorophyll that breaks the water molecule into oxygen and active H. In the present experiment it was found that in the absence of light starch was not detectable. It has been shown in the present paper that it is not only the intensity of light but also the quality (wavelengths) of light crucial for this process.
In comparison with the full exposure of the leaf, the exposure of the leaf either to blue or red filters showed less of starch. References Arnon, D. I. (1960). The role of light in photosynthesis. Sci Amer. 203: 105 – 118 Bohning, R. (1949). Time course of photosynthesis in apple leaves exposed to continuous illumination. Plant Physiol. 24:222 Calvin, M. (1956). The photosynthetic carbon cycle. J. Am. Chem. Soc. 78: 1895 Grasshoff, K. (1983). Determination of oxygen (chapter 4). In: Grasshoff, K. , Ehrhardt, M. , Kremling, K. (eds. ). Methods of seawater analysis. Second, revised and extended edition. Verlag Chemie, New York.
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