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. The height of he cress, as well as its colour and length of roots, will show me in which amount of water or acid the cress grew best. I will then be able to tell, to some extent, how acid rain affects plant growth. EQUIPMENT: To conduct this investigation I will need: 6 test tubes Test tube rack 60 cress seeds 60 mls of water Measuring cylinder Pipette Cotton wool Bungs for test tubes Sulphuric acid SAFETY:
To ensure safety throughout this experiment I will wear goggles at all times when setting up my test tubes and handling the acid. FAIR TEST: To make this investigation fair, I will set up all the test tubes at the same time so that my cress seeds all have the same amount of time to grow. I will keep all my test tubes in the same conditions, and use the same amount of cress seeds (10) in each. Also, I will use the same amount of water (5mls) in all the test tubes. RANGE AND REPEATS: To obtain a wide range of evidence, I will get results from one other group who have also conducted this investigation.
By comparing their results with my own, I will be able to see if there is a pattern or trend between the test tubes and the amount of sulphuric acid used. DIAGRAM: This diagram shows the set up of my test tubes: 1 2 3 4 5 6 PREDICTION: I think that the cress seeds will grow best in test tube number 1, which contains no acid. This is because evidence has shown that acid rain damages plants, especially their roots, which it eats away at. Therefore, my prediction is that the best cress will come from the test tube with no acid, and the worst cress will come from test tube number 6, which contains 5 drops of acid.
SCIENTIFIC BACKGROUND ON ACID RAIN: Sulphuric acid and nitric acid are formed when sulphur dioxide and nitrogen oxides react with water in the atmosphere. When it rains, these fall to the ground as acid rain and are deposited in the soil. This then washes away nutrients, such as calcium and magnesium that are present in the soil. It raises the concentration of aluminium in the soil, which is poisonous to plants. The roots of the trees then absorb aluminium. Because of this and the nutrients being washed away, the trees and plants are starved to death.
All plants and trees, especially coniferous ones, are affected by acid rain, which can also take the form of snow or fog. Almost half the trees in Germany’s Black Forest have been destroyed by acid rain. When calcium and magnesium are washed away, they are replaced by hydrogen atoms, These hydrogen atoms are useless, and inhibit photosynthesis Other things present in acid rain, such as nitrogen oxide and nitric oxide can force trees to grow, even when the trees and plants do not have the necessary nutrients to do so.
As a result, trees and plants sometimes grow well into late autumn, when instead they should be preparing for the winter frosts. OBTAINING EVIDENCE: To give the cress seeds sufficient time to germinate, I left all my test tubes in the same conditions for a week. After a week, I removed each piece of cotton wool from the test tubes and took measurements to find out how many had germinated in each test tube and the height they had grown to. 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.