Two Petri dishes were prepared by lining them with filter paper. Cress seeds were evenly spinkled over them both. One dish was then watered with distilled water, while the second was watered using dilute acetic acid. The seeds were then left for five days at room temperature.
Upon examination after five days it was clearly seen that the cress seeds that had been given distilled water had all germinated. However, seeds watered with acid had not germinated at all.
The seeds on the left had been watered with distilled water. The seeds on the right had been watered with dilute acetic acid
Seeds need water to germinate. However, the presence of acid prevents germination taking place. It is believed that this is because acid kills root cells. Without root cells the seeds are unable to effectively absorb water.
When we burn fossil fuels (coal, oil or natural gas) carbon dioxide and water vapour are released. This is known as combustion. However, coal often contains the element sulphur as an impurity. When the coal burns, this sulphur reacts with oxygen to make a highly acidic gas called sulphur dioxide. This gas dissolves in the water droplets that form clouds. When these droplets fall as rain we have the phenomenon called 'acid rain'. Acid rainfall has been blamed for damage to many forests across Europe.
For more information on acid rain, try this site:
CEH Schoolnet - Acid Rain (Basic)
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