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Cress seeds investigation.

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PLAN: The aim of this investigation is to find out how acid rain affects the growth and development of plants - in the case of this investigation, cress seeds. I will set up 6 test tubes, each with a different concentration of acid in. The amount of sulphuric acid in each tube will increase at the rate of one drop per 10 mls of water. For example, the first test tube will have no acid, the second will have one drop, the third will have 2 drops and so on, gradually increasing up to 5 drops in the final test tube. METHOD: To do this experiment I will take 6 test tubes and put water and different amounts of acid into each of them. I will put 5mls of water into the first test tube, with no acid. For the second test tube I will put 10mls of water into a measuring cylinder along with one drop of sulphuric acid. I will allow the acid and water to combine, and then put 5 mls of the mixture into the test tube. I will repeat this for each of the 4 remaining test tubes, increasing the amount of sulphuric acid by one drop per test tube. OBSERVATIONS TO BE MADE: After leaving my test tubes for a suitable amount of time (approx. 1 week), to let them grow, I will measure the height of the cress in each test tube. ...read more.


To do this I used a copper rod to remove the cotton wool from the test tube, and then also to pull the seedlings (including roots) from the cotton wool. I then measured the total height of each seedling in mm, using a ruler. These are my results: Test tube 1: Number germinated: 9/10 Height of seedlings: 79 ; 70 ; 79 ; 66 ; 39 ; 32 ; 33 ; 15 ; 36 Test tube 2: Number germinated: 8/10 Height of seedlings: 64 ; 40 ; 49 ; 45 ; 51 ; 50 ; 38 ; 25 Test tube 3: Number germinated: 10/10 Height of seedlings: 12 ; 12 ; 12 ; 9 ; 15 ; 20 ; 15 ; 7 ; 10 ; 3 Test tube 4: Number germinated: 10/10 Height of seedlings: 1 ; 5 ; 7 ; 6 ; 27 ; 1 ; 10 ; 7 ; 20 ; 15 ; Test tube 5: Number germinated: 9/10 Height of seedlings: 12 ; 3 ; 7 ; 5 ; 7 ; 5 ; 3 ; 4 ; 6 Test tube 6: Number germinated: 0/10 Height of seedlings: 0 I then took the averages of the height of the seedlings in each test tube. Average height in test tube 1: 49.9mm Average height in test tube 2: 45.25mm Average height in test tube 3: 9.9mm Average height in test tube 4: 11.5mm Average height in test tube 5: 5.8mm Average height in test tube 6: 0mm This is ...read more.


My results support the original prediction that I made. I said that the cress would grow best in the control test tube, and as the results show, it did. I also said that the test tube containing the most acid would produce the worst seedlings, which was also correct. EVALUATING EVIDENCE: My results were not completely accurate. Although the basic trend showed that the more acid the seedlings were put in, the less they grew, my average heights went up slightly when, theoretically, they should have gone down. For example, they went up from 9.9mm to 11.5mm, and then down again to 5.4mm. Therefore, the graph that I drew does not have a completely accurate curve. This is also true for the other set of results that I gathered. I could improve the accuracy of this investigation by doing several things differently. I could use more test tubes, giving me a wider range of results, and I could also use a smaller amount of acid per test tube - for example, I could increase the acid by .5 of a drop per tube. This would give me more accurate results. Because my results were slightly anomalous, they are not sufficient enough to support a firm conclusion. Because the results did not follow a set pattern, they are not entirely reliable. To improve on this, and make my results more accurate, I could be very meticulous when measuring out the acid, and also make sure that I treat all the test tubes equally. I feel that this investigation went quite well although my results could have been slightly more accurate. ...read more.

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