Photosynthesis - Research Paper Example

Photosynthesis Photo means light and synthesis means the process of producing a chemical compound usually by the union of simpler chemical compounds (Sage Dictionary). Photosynthesis is a phenomenon unique to the Kingdom Plantae, and that too is specifically limited to those plants which are green in colour. However, in addition to plants, certain algae belonging to Kingdom Protista and a few bacteria are also capable of photosynthesis. Photosynthesis is defined as the process of converting light energy into chemical energy in the form sugar or starch by the green plants by using Carbon-di-oxide (CO2) and water (H2O). The presence of a unique pigment, which imparts the green colour to plants, Chlorophyll, is essential for Photosynthesis to take place. Therefore the plants, algae and some bacteria are the only self sufficient living organisms on this planet in terms of their food requirement. All other living forms which include non pigmented plant forms and animals including human beings depend on external sources for their food requirement. The process of photosynthesis also results in the production of oxygen (O2), which is essential for animals to sustain life. Plants and animals therefore live in a symbiotic relationship i.e. they are dependent on each other for survival. Majority of photosynthesis occurs in the leaves of the green plants present in nature. The leaves have specialized structures called chloroplasts which store the unique pigment, chlorophyll. The chlorophyll pigment although appears green to the naked human eye, actually absorbs red and blue light from the light spectrum and does not absorb the green light which is reflected back. The energy absorbed from the red and blue lights is the one utilized for photosynthesis. The upper and the lower surface of a typical leaf are known as epidermis or the outer covering. Between the upper and the lower epidermis lies the mesophyll which harbours the chloroplasts and the vascular bundle or veins. These veins are responsible for the transportation of water and nutrients to other parts and cells of the plant. The lower epidermis has minute holes known as stomata which communicate with the atmosphere for gaseous exchange. Carbon-di-oxide is taken in and oxygen is released into the atmosphere. The chemical reaction which takes place inside the leaf is as shown below: 6CO2 + 6H2O (in the presence of light) → C6H12O6 +6O2 As obvious from the above equation, it is clear that six molecules of carbon-di-oxide combine with six molecules of water, in the presence of chlorophyll and light to yield one molecule of sugar and six molecules of oxygen. The sugar produced is used for cellular respiration in the plant cells which converts the sugar into ATP (Adenosine Tri Phosphate) which is the fuel used by all living cells. It is to be noted here that respiration in plants too utilizes oxygen as in other living organisms including animals. Photosynthesis involves an overall process of two stages. In the first stage, the ‘Light Reactions’ presence of light is an essential element. Light stimulates the formation of energy carrying molecules which are needed in the second stage. The second stage known as ‘Dark Reactions’ is a light independent process and is the final step in the production of sugar. Experiment It is obvious from the above information that a number of factors are essential for photosynthesis to occur. Some of these factors can be studied and proven experimentally by simple experiments with readily available equipment which does not need any sophisticated apparatus. In such an experiment the two factors, CO2 and intensity of light were studied for their role in the process of photosynthesis. Materials and Methods 1. Green pond weed collected from a local pond. 2. Baking soda (Sodium bicarbonate). 3. Water. 4. Test tube, glass and rubber tubing and a pinch clamp. 5. Light bulbs of 40, 60 and 100W power. 6. Red and green transparent cellophane sheets. An adequate amount of the pond weed just enough to fill an inverted test tube was cut and placed in the test tube. 1 g of baking soda was added to 500 ml of ordinary tap water and this solution was used to fill the test tube. The baking soda solution produces more carbon-di-oxide for utilization by the pond weed for photosynthesis. A 10 cm long piece of rubber tubing was attached to 10 cm glass tubing which was passed through a rubber stopper. Baking soda solution was sucked into the glass tubing and the pinch clamp was applied to the rubber tubing to keep it at the required level. One end of the pond weed was inserted into the glass tube containing the solution and the rubber stopper was put firmly in place on the test tube mouth to seal the assembly. A range of experiments were conducted on this basic setup by changing the distance of light source (bulbs), intensity of light source (powers of bulbs), changing the frequency of light exposure (by covering the test tubes with blue/green coloured cellophane sheets) and by varying the time duration of light exposure. Bubbles of gas released from the plant were counted as a parameter for measuring the amount of photosynthetic activity in the pond weed. Picture Courtesy: http://www.scienceman.com/science10/images/ima_elodea.gif TABULATED RESULTS: Experiment Light Source Test Tube Distance Time of counting No. of bubbles 1 100 W Clear 10 cm 20 cm 15 minutes 47 28 2 100 W 40 W Clear 10 cm 5 minutes 26 8 3 100 W 40 W Clear 20 cm 5 minutes 102 48 4 100 W Red cellophane sheet covered tube 10 cm 5 minutes 54 5 100 W Green cellophane sheet covered tube 10 cm 5 minutes 23 6 100 W Red cellophane sheet covered tube 20 cm 5 minutes 8 7 100 W Green cellophane sheet covered tube 20 cm 5 minutes 0 Table 1: Number of CO2 Bubbles Produced by Varying Light Source, Time & Distance The data from Table 1 was extracted to obtain a comparison chart for three sources of light as follows: Light Color Distance Bubbles Clear 10 cm 26 Red 10 cm 54 Green 10 cm 23 Clear 20 cm 102 Red 20 cm 8 Green 20 cm 0 Table 2: Effect of Different Light Sources at 5 Minutes’ Exposure. (The plants were exposed for 5 minutes each for clear, red and green lights and the distance were changed for all light sources from 10 cm to 20 cm). Fig. 1 No. of Bubbles in 5 Minutes with Various Light Intensities (White, Red & Green) Analysis of Experiments In the first experiment, more bubbles (47) were counted when the distance of the light bulb was 10 cm as compared with 20 cm (28 bubbles) (Fig. 2). This shows that more intensity of light and its close proximity stimulated more photosynthetic activity in the pond weed. Fig. 2: Effect of distance on number of bubbles with a 100W light source. In the second experiment, more bubbles (26) were produced when the light source was a 100 W bulb, as compared to the 40 W bulb (8), further providing confirmation that more the light more is the photosynthetic activity (Fig. 3). Fig. 3: More bubbles with a 100 W bulb as compared to 40 W at 10 cm. in 5 minutes The third experiment was a repetition of the second one, with the only difference that the distance of the light source was increased to 20 cm. However this failed to produce the expected decrease. More photosynthetic activity was recorded when the 100 W bulb was used (Fig. 4). Therefore the intensity and not the distance of light source positively influence the photosynthetic activity. It shows that sufficient light, even from a distance provides enough stimulus for photosynthesis. Fig. 4: More bubbles with a 100 W bulb as compared to 40 W at 20 cm. in 5 minutes In experiments 4 to 7, red and green lights were used as compared to white light to find out if there was any difference due to these particular frequencies on the process of photosynthesis. Fig. 5: More bubbles with red filter as compared to green at 10 cm. in 5 minutes At 10 cm as well as 20 cm distance, with the same wattage, but different colours, it was clear from the results that red light produces more photosynthetic activity as compared to the green light (Figs. 1 & 5). At 10 cm distance, red light elicited 54 bubbles as compared to 23 when the green filter was used. Similarly at the distance of 20 cm, no bubbles were produced at all when the green cellophane sheet was used, while the red one still elicited the production of 8 bubbles. Conclusions It is clear from the experimental results that light and carbon-di-oxide are essential for the process of photosynthesis. The Sodium bicarbonate solution is a ready source of CO2 which was utilized by the pond weed in this experiment. An increase in the intensity of light by either increasing the wattage of the bulb or reducing the distance between the plant and the bulb resulted in an increase in photosynthetic activity showing the importance of light in this process. It is also obvious from the experiment that the red light produces more photosynthetic activity as compared to green light. We can conclude that the red spectrum of light plays a more important part in the process of photosynthesis. Photosynthetic activity is also directly proportional to the amount of light and the CO2 availability, as was shown in this experiment. References: Photosynthesis, Online article available at: http://biology.clc.uc.edu/Courses/bio104/photosyn.htm Photosynthesis, Online article available at: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html Picture Courtesy: http://www.scienceman.com/science10/images/ima_elodea.gif Experiment Planning & Analysis The experiment I have designed is likely to yield accurate data as it is an established and tried laboratory procedure at this level. A fresh pond weed collected from a local pond can sustain itself in the experimental setup as fresh water, free from any chemicals will be used in the experiment. The only addition will be an appropriate amount of Sodium bicarbonate (baking soda) in order to enrich the bathing solution with Carbon-di-oxide which is a vital component for photosynthesis to occur. Light sources in the forms of incandescent bulbs of 40 and 100 watts will be used in the experiment. These bulbs are an ideal source of white light which has all the components of the white light spectrum. Cutting off certain spectrums will be established by covering the test tube with red and green transparent sheets which will block these particular spectrums and thereby prove which particular light frequency is more pertinent to the process of photosynthesis. The process of photosynthesis is such that more oxygen will be released under the enhanced stimulus of light as well as excess carbon-di-oxide which has been achieved by adding baking soda. The released oxygen will have only one source to escape that is through the glass tubing, which will be visually evaluated by counting the number of bubbles escaping. The dependent variables will be light source, distance of the light source, amount of dissolved carbon-di-oxide, blocking of certain frequencies of light with coloured sheets and the temperature of the bathing solution which will be kept at an optimum level. The independent variables will be the condition of the pond weed, the amount of chlorophyll content in it, and the amount of carbon-di-oxide released by the dissolution of baking soda. DECIDE ON THE OF VALUES FOR YOUR VARIABLES IDEALLY A MINIMUM 5. 1. The number of bubbles released from the reaction. 2. The amount of light exposure as controlled by wattage of lamps. 3. The amount of baking soda dissolved in water, directly influencing the amount of CO2. 4. The distance of the light source. 5. The amount of green foliage in the weed. There are minimum hazards in this experiment. The only concern is to handle the light source carefully and use fully insulated wires, switches and materials in order to avoid electric shock. The fitting of the rubber tubing over the glass tubing also has to be done carefully as accident can occur during the manoeuvre. Utmost care should be taken while sucking the water up to a particular level inside the glass tube as a vigorous effort can lead to the soda solution entering the experimenter’s mouth. It can be slightly corrosive and cause injury. Care should also be taken to place the experimental setup away from small children. In evaluation you should of also included how successful do you feel the method part of the study was? This method of evaluating the photosynthetic process by changing the light sources, increasing their distance and using red and green filters yielded expected changes in the rate of photosynthesis as evident from the increase/decrease in the number of bubbles escaping from the experimental setup inside the glass tube. The bubbles were clearly visible and countable over the time spans set up for the evaluation. Could you improve your techniques? The technique could be improved if some method of measuring the frequency of light was available, which could be correlated and more exacting parameters ascertained. The experiment can be done in a better way in a proper biology laboratory where apparatus designed specifically for such experiments are available. How accurate was your experiment The results of my experiment were quite accurate and in accordance with the established facts about the process of photosynthesis. What problems did you encounter, if any, what improvements or recommendations have you included as a result of these problems The only problem was the selection of the pond weed and choosing the appropriate size which was ideal for the test tube. Too large and too small stems are likely to yield inaccurate results. The stem size should be just enough to be placed with ease inside the test tube and it should not choke the inside of the test tube. Wrapping the coloured cellophane sheets around the test tubes is also a cumbersome procedure as they have a tendency to loosen up. This problem was solved by using a couple of rubber bands at both ends. All variables were well controlled after some experimentation. The bulb wattage was clearly marked on the bulbs and the distance was measured with a ruler. Uninterrupted power supply was used so that the bulbs don’t go off due to a power failure. The amount of carbon-di-oxide was beyond my control, so freshly prepared solutions of baking soda were used in all the experiments. WAS YOUR INITIAL HYPOTHESIS CONFIRMED? My initial hypothesis was confirmed as the results were consistent with the established facts of photosynthesis. Read More