The pituitary gland is connected to the hypothalamus. The pituitary is a pea sized organ that controls hormones. What the hypothalamus does is control body temperature, thirst, hunger, and other homeostatic systems, and involved in sleep and emotional activity. The hypothalamus needs the pituitary to be active because the pituitary makes the decision of what people are feeling in their body, and the hypothalamus releases those feelings into the body.
Nitrogen must be converted into nitrates before organisms can use it. If soil lacks nitrogen fixing bacteria, then it has few nitrates for the plants to take in.
