Photosynthesis - Lab Report Example

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The rate of photosynthesis is increased by increase in temperature until an optimum temperature is reached. If the temperature is increased beyond the optimum temperature the rate of photosynthesis will decrease. Photosynthesis is the process that is used by plants to make food. Through this process plants trap light energy to convert it into organic energy in the form of glucose. The rate of photosynthesis is affected by factors like: carbon dioxide concentration, temperature and light intensity. If two of these factors are kept constant while one of the factor is increased, the rate of photosynthesis will increase but up to certain point. At that point the two factors that are kept constant will act as limiting factors and they will be limiting the further increase in rate of photosynthesis.
Methods and Materials
Apparatus: Photosynthometer, Beaker of water, Elodea, Hot water, Ice, Thermometer, Lamp with wattage bulb of 100.
Method: In this experiment we kept temperature as an independent variable. We cut a piece of elodea and kept it in a beaker of water and anchored it with a paper clip. We placed the lamp 7cm away from the beaker and the lamp was kept at this point throughout the experiment. In order to keep the concentration of CO2 constant we assumed that the CO2 in the water in the beaker remained same throughout the experiment. We changed the temperature of the experiment by changing the temperature of the water in the beaker. We obtained hot water in the beaker by pouring hot water from the kettle in the beaker and we obtained cold water by adding ice to the beaker. We measured the rate of photosynthesis by measuring the rate of oxygen given off by the elodea. In order to measure the volume of air given off we used a photosynthometer. In order to prevent bubbles to appear in the tubing of photsynthometer we kept the tubing in the water.
We started out experiment with initial temperature of 40 °C. We used a thermometer to ensure that the temperature of water in the beaker was 40 °C and then placed elodea that has previously kept in dark into the beaker. We used a piece of elodea that was previously kept in the dark because this ensured that the plant had not been previously photosynthesing and it avoided us having unfair results. Once we placed elodea in the beaker we immediately started noting the time it took for 5mm3 of air to be trapped in photosynthometer.
Results
With the temperature kept at 40 °C the experiment was repeated ten times and the time taken by the photosynthometer to trap 5mm3 of oxygen was noted.
No. of trials
1
2
3
4
5
6
7
8
9
10
Time noted in mins
4.3
5.0
5.9
6.9
7.0
7.0
7.1
7.3
7.3
7.5
The average time taken at 40 °C was calculated and it was noted as 6.5 minutes. The experiment was repeated at different temperatures like 15 °C, 20°C, 30 °C. To ensure constant temperature was maintained during each experiment a thermometer was placed in the beaker to note the temperature. The different temperatures of water in the beaker were obtained by adding warm and cold water to the beaker. The average time for ten trials at each temperature were noted in a table as follows.
Temperature of experiment (°C)
15
20
30
Average time (mins)
20.4
7.5
5.6
Conclusion: As we increased the temperature from 15 °C to 30 °C the rate of photosynthesis increased as the time taken for 5mm3 of oxygen to appear in photosynthometer decreased from 20.4 minutes to 5.6 minutes. But when the temperature of the experiment was increased to 40 °C the average time of the experiment increased to 6.5 minutes. This confirms our hypothesis that temperature is a factor that affects the rate of photosynthesis and increasing temperature increases the rate of photosynthesis until an optimum temperature is reached. In this experiment the optimum temperature is 40 °C because at this temperature the rate of photosynthesis starts to decrease.
The rate of photosynthesis increases with temperature because enzymes are used in the process of photosynthesis to form glucose from water and carbon dioxide. The formula for photosynthesis is 6CO2 + 6H2O is equal to C6H1206 plus 6O2. Enzymes act as catalyst for this reaction and help the reaction move in forward direction. A rise in temperature allows enzymes to absorb more energy to help hydrogen and carbon dioxide molecule react faster to make end products of photosynthesis. But these enzymes have an optimum temperature after which they start to change their shape. Once these enzyme start to change their shape they cannot accept hydrogen and carbon dioxide molecules at their active sites and they can no longer act as catalyst for photosynthesis and thus the rate of photosynthesis start to decrease after the optimum temperature.
Relevance
In everyday life we use soaps and detergents to clean grease. In an article on about.com it has been mentioned that detergents contain surfactants that lower the surface tension of water. These surfactants make water less likely to stick to itself and make it more likely stick to the grease and oil. The surfactants also contain enzymes to help remove protein related stains and to help make water stick to grease. The hydrophobic part of the surfactants are repelled by water and attracted to oil and grease. The surfactants help bind the water to grease stain on clothes and dishes so that when mechanical energy like scrubbing is added to the washing process, the grease stain is easily removed in the rinsed water. Using warm water help remove grease stain faster because warm water melt fats in the grease stain easily and the melted fat is then easily removed by the detergent. The use of detergent in removing grease stain can be related to the photosynthesis experiment mentioned above because just as increasing temperature increases the rate of photosynthesis, increasing the temperature of water used in cleaning help remove grease stains faster. Thus in both cases, that is, photosynthesis and cleaning stains, temperature play a crucial role in determining the efficiency of the processes.
Reference:
1. Smith, A. L. (1997). Oxford dictionary of biochemistry and molecular biology. Oxford [Oxfordshire]: Oxford University Press. pp. 508. ISBN 0-19-854768-4. "Photosynthesis - the synthesis by organisms of organic chemical compounds, esp. carbohydrates, from carbon dioxide using energy obtained from light rather than the oxidation of chemical compounds." 
2. Nealson KH, Conrad PG (December 1999). "Life: past, present and future". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 354 (1392): 1923–39. doi:10.1098/rstb.1999.0532. PMID 10670014. PMC 1692713. http://journals.royalsociety.org/content/7r10hqn3rp1g1vag/.  
3.Anne Marie Helmenstine; “How Detergents Clean” Retrieved November 7, 2009 from About.com website : http://chemistry.about.com/od/howthingswork/f/detergentfaq.htm Read More