 You need to also be able to talk about the effects of acid rain. So plants are damaged in a few ways. The leaves, if you spray acid on the leaves, they get damaged, and that reduces the ability of the plant to do photosynthesis. Damaging the leaves also damages the coating on the leaves, and that leads to ions being leached from the leaves, again reducing the ability of the plant to do photosynthesis. So you have essential metal ions, so things the plant need, like magnesium and potassium and toxic metal ions, that can be mobilized off of the clay surfaces. And I'll show you a picture of this in a second. If you remove essential ions and wash them away and release toxic ions, then that can cause damage to plants. So we'll talk about leaching. So in leaching, you have clays in the soil that have a surface negative charge, and you get positive cast ions attached to those negative surfaces. And they can be good things like potassium or sodium, which are required in amounts in plants, or they can be things that are toxic, like aluminium and cadmium. So they stick to the surface of the clay. When you wash in an acid, you can get replacement of those cast ions with hydrogen ions. So they can stick to the surface of the clay, and that means that the cast ions that you have there, they go into the soil water. And this could be a good thing if it's something like potassium, because then the plant can absorb that potassium. But it can also be a bad thing if you're mobilizing things like aluminium, which is very toxic. So aluminium isn't good, if you have it in the soil water, the plants can absorb the aluminium, and that can cause damage to the plants. So why is aluminium toxic? It disturbs the defence mechanism of the plants used to fight disease. They can damage bacteria that decompose vegetation and reduce the ability of the bacteria to recycle nutrients. In fish, you can stop the ability of the gills to work, leading to suffocation of the fish. The ions can be washed into lakes and streams, and that can make them toxic with high levels of aluminium. And also acid washing into lakes and streams can be bad, because it will kill off the fish as well. So it will kill the eggs and the fry, which means you don't have fish there. So there are lakes in some countries that don't have any living things in them, because of the amount of acid that's being washed into them due to acid rain. Acid rain also has effects on the built environment. So limestone and marble are made out of calcium or magnesium carbonate, and you shove any acid near there, you get this reaction here. So you've got a metal carbonate with an acid, so you get a salt, carbon dioxide and water being produced. And you can see this very dramatically in this picture here. So we have a picture of a statue over here, so from 1908 to here from 1969, and you can see all the features have been washed away essentially, and that's because the acid rain has dissolved away the features. The calcium sulfate that's produced can dissolve and find its way into cracks inside buildings. When the water evaporates away, that means you're left with the deposit that expands in size, and that leads to cracks and fracturing. So you can see on the surface here where we've got these cracks that are fractured off the surface of the bricks that are there.