In plants, where does fixed Nitrogen come from , how does it occur, and where does it occur?

Question

the answer doesn't seem to be in my notes or the textbook. I have no idea what she means "where does it occur" but it might be on the test appearantly

Answer 1

Fixed nitrogen goes in through the roots for the plants to use. It can come from nitrogen fixing bacteria that live on the roots of legumes (soy beans and others) or from the fixation from nitrogen going through the air, or from fertilizers that are put on the field.

Answer 2

Very simple. It's a natural process that bacteria provide through living in some plants. Legumes or the "bean" family are best know for it.