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Investigating a pollutants effect on cress seeds

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Aim: To investigate the effect of phosphates from detergent liquid, at different concentrations, on the germination of cress seeds. Hypothesis: I predict that, at lower concentrations, the detergent liquid containing phosphates will have a small positive effect on growth. However, I believe at stronger concentrations, the detergent liquid will have a negative effect on growth, causing stunted and malformed cress plants. Introduction: Many commercial detergent liquids contain phosphate. Phosphate, (PO43-) is an important inorganic macronutrient which is needed to help plant growth, and as such is a part of the essential small molecule ATP. Although it can be hard to test whether minerals are important in animals, it is far easier to test the effects of phosphate (which in this case will form part of a pollutant). The main reason for my hypothesis is that phosphates can cause eutrophication when found in a water supply, and as such I believe that small percentages (10-20%) detergent liquid will case minor positive changes in growth. However, there are other chemicals present (such as Benzotriazole, colorants and purfumes) in detergent liquid that may cause the cell wall and cell membrane of the cell to break down allowing the cell contents to spill out and the leaves will appear discolored. This may also cause the cress to grow slowly or die prematurely. There may also be an appearance of leaf tip necrosis, iron deficiencies, and some seeds may fail to germinate due to imbalances in the pH of the "soil". You don't say why there may be a pH imbalance. Cress is a seed which is exceptionally easy to cultivate, and as such will be the plant used for my experiment. Germination in plants occurs when there are suitable conditions. Germination requires water, oxygen and an appropriate temperature. Water is necessary because the final stage in the creation of a seed is a drying out of embryonic tissues. ...read more.


Twice every day, measure the temperature of the environment, note and fix any anomalies that occur. 10. Every other day, add an extra 5ml of distilled water to each dish, at the same time each day. 11. After 7 days, count the number of seeds that have germinated and measure heights of the seeds from base to highest point, including root. Record. I plan to repeat the experiment at each concentration twice, as mentioned in my justifications. Concentration detergent % 0 (control) 10 20 30 40 50 Water (ml) 20 18 16 14 12 10 Detergent (ml) 0 2 4 6 8 10 Risk Assessment * Some detergents can cause irritation to skin. To prevent this, rubber gloves and goggles will be worn throughout the experiment to prevent painful skin irritation and contact with the eyes. * Spillages must be cleaned up as soon as they occur as they may damage surfaces and skin. * All breakages of glass pipettes must be cleared away carefully as soon as they occur to prevent injury. Results: To calculate an average, I must first calculate the sum of all the numbers desired as part of the average, and then divide by the number of figures used. For example: 48.3+52.1 = 100.4 100.4/2=50.2 Test 1 - Control Height (mm) Test 1 Height (mm) Test 2 Height (mm) Average 1 48.3 52.1 50.2 2 57.8 54.6 56.2 3 39.8 60.1 49.95 4 46.7 53.8 50.25 5 53.8 48.9 51.35 6 61.3 70.1 65.7 7 56.8 68.5 62.65 8 33.9 67.4 50.65 9 65.4 65 65.2 10 67 45.8 56.4 11 64 51.2 57.6 12 41.3 53.9 47.6 13 33.3 44.4 38.85 14 54.8 65.3 60.05 15 67.2 75.2 71.2 16 43.2 45.6 44.4 17 45.8 67.4 56.6 18 54.5 45.7 50.1 19 78.1 77.2 77.65 20 67.1 0 33.55 21 55.2 0 27.6 22 0 0 0 23 0 0 0 24 0 0 0 25 0 0 0 Average (mm) ...read more.


* I believe that using a microscope and the small measuring eyepiece was a disadvantage as it wasn't terribly accurate and results could have been skewed by any small movements. * The packet of seeds I was using recommended a 2 week gestation period for the seeds before they are edible. Perhaps after 2 weeks, rather than 1, the growth may have evened out somewhat. * This experiment only showed me the effect of a detergent as a whole rather than the actual effect of phosphates. While this is important in reality, as it is often detergent as a whole that gets washed into water sources, I cannot be sure that it is the pentasodium triphosphate giving me these results and not an alternative chemical. * Only using 50 seeds per concentration in the overall, single experiment has obvious percentage error and data collection limitations. * The cress variety used in this experiment doesn't grow in the wild and thus wouldn't come into contact with phosphates in the same way wild plants would. This means that the varieties of plants and algae that grow in the wild and come into contact with phosphates as part of irrigation systems, lakes, ponds and rivers may not respond in the same way as the cress I used to experiment with. Further Work: * If I was to do this again, I would have measured the dry mass to get more accurate results for growth. Obviously drying them removes the water and gives a more valid and reliable measurement, and using mass instead of length is both simpler and more useful than measuring length. * I would also try and do as many repeats as possible, as using only 50 seeds for each concentration could still have given quite significant percentage error. For example, 1 anomaly from this would have given a 2% error, whereas 1 anomaly from 500 would only be 0.2%. * If repeating this experiment I would carry it out over a longer period of time, for example 2 weeks as opposed to one. ...read more.

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