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Investigate the rate of photosynthesis in Elodea under different circumstances using pH as the measurement.

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MEASURING THE RATE OF PHOTOSYNTHESIS IN ELODEA PLANNING A: AIM: To investigate the rate of photosynthesis in Elodea under different circumstances using pH as the measurement. INTRODUCTION: The process in green plants and algae that allows them to produce their own food sources and continually regenerate oxygen in the environment is called photosynthesis. This process, undertaken by green plants, nourishes almost the entire living world either directly or indirectly, as the path of the food chain is traced from plants up through animals. Photosynthesis comes from two words, photo meaning ''light'' and synthesis meaning "to make". Photosynthesis occurs to furnish life, directly or indirectly, with chemical energy in organisms. Plants use photosynthesis as a means of obtaining energy from sunlight, converting it and store it as chemical energy - 'packets' called ATP. These energy packets are, in turn, used with carbon dioxide to build a variety of chemicals in the plant, including carbohydrates, fats and proteins - the common compounds we call food. ...read more.


Chlorophyll only absorbs the red and blue ends of the visible spectrum but not the green light in the middle, which is reflected back. If the light level is raised the rate of photosynthesis will increase steadily but only to a certain point. In water plants, photosynthesis can be measured using pH as carbon dioxide in water makes a slightly acidic solution - carbonated mineral water. After photosynthesis has occurred, a change will occur in the concentration of carbon dioxide and the rate of photosynthesis can be determined by recording the change in pH. HYPOTHESIS: If the photosynthesis has occurred, then the solution will be more basic (pH will increase). In photosynthesis, carbon dioxide is exhausted and thus the combination of water and carbon dioxide (carbonic acid) will contain less carbon dioxide. The less amount of carbon dioxide in the solution, the less acidic it becomes and thus the solution will become more basic and the pH will increase. If photosynthesis has not occurred, then the solution will be more acidic (pH will decrease). ...read more.


This was probably due to contamination of the pH meter. ERRORS AND THEIR EFFECTS IMPROVEMENTS Difference between photosynthesis and respiration. Plant only respires at night and there is an assumption that is respires during the day but at a lower rate than photosynthesis. Include more test tubes in which respiration is measured, both at night and during the day to confirm assumption. Experiment only carried out for 22 hours as opposed to 40 so results were not as precise. Carry experiment out for 40 hours to gain more accurate results. The Elodea was dying during the process of drying therefore affecting its ability to photosynthesise at an optimum rate. Some carbon dioxide was released before the plant was placed in the test tube, affecting the amount of carbon dioxide in the solution. Stopper flask/test tube immediately after mixing solution and inserting plant. Miscalculation of pH due to contamination, pH meter was not placed in buffer each time thus affecting pH recorded. Ensure the meter is placed in buffer each time after recording pH. ...read more.

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