Nitrogen is special because it is necessary for growth and reproduction. It's needed for plants and animals to survive. The main function for the atmosphere i believe is to give oxygen and nitrogen.
Ecosystems need producers because they are the start of the food chain.
Producers are consumed by first consumers, the second consumers and so on.
Well it’s obvious that they both use Photosynthesis to make there own food, and also they both use chemosynthesis the produce there own food. Very simple. :)
