[Music] there was a constant recycling of chemicals that was going on on the planet now my corn isms such as bacteria play a really key role in this because what they do is they break down complex organic molecules and return the elements to the environment so they then can be reused again elements on the planet I recycle between the living world and the nonliving world so the elements may be in the air the water and the soil and the rocks but they could end up getting back into living organisms but then they might end up getting returned back to the air and the soil and the rocks again so they can element can move between the living and the non-living we're going to look at two specific elements and how they are recycled we're gonna look at carbon and nitrogen it's a very very important element nitrogen you need it to make many biological compounds such as DNA proteins amino acids and vitamins the thing is 78% of the air is nitrogen so most of our atmosphere is not shown but it's so unreactive and we can't do anything with it we breathe it in we breathe it out we do nothing with it but bacteria can convert into useful form called nitrates so they'll start off again with our gas in the nr this time we're gonna start with nitrogen gas now the nitrogen gas is converted into nitrates in a process called nitrogen fixation is it done by bacteria in the soil or root nodules of particular plants called legumes that have these very special bacteria living inside their roots nitrogen fixation also occurs when lightning strikes the ground you get night nitrogen gas being fixed as well but the point is that bacteria and lightning can cause nitrogen gas to be converted into nitrates and plants can use nitrates they can't use nitrogen gas but they can use the nitrates too and they can use it to make proteins and other structures now again then that can get passed along the food chain via feeding animals and plants can die or excrete and those nitrates are stored in there can get returned to the soil in the form of ammonia and there are some bacteria that do that process as well these are decomposing back to here our decomposers that can break down dead organisms and release nitrogen in the form of ammonia back into the soil then that ammonia needs to be converted back to nitrates which happens in a couple of stages goes to nitrites first then it goes to nitrates and again that's done by some particular type of bacteria called nitrifying bacteria nitrates can also get returned back to nitrogen gas as well and that is what we call denitrification and so there's one other type of bacteria that does that and those are the denitrifying bacteria so in total we've got four types of bacteria involved in the nitrogen cycle well the nitrogen fixing bacteria that convert the gas into nitrates we've got a decomposing bacteria that convert the nitrates in the dead organism into the ammonia in the soil we've got nitrifying bacteria they can then take that ammonia back to the useful nitrates and then we also have D nitrifying bacteria that can convert excess nitrates in the soil back into nitrogen gas in the atmosphere so you need to know these four types of bacteria on what they do in the nitrogen cycle