Can someone please help me with this these questions

In what for do plants utilize nitrogen? why do they need nitrogen?

Idon’t know the answer and i’ve been stuck on it for a while now skskskskks

The vaccine in a flu shot contains weakened flu viruses. how does a flu shot work with the immune system? a. it destroys lymphocytes. b. it destroys macrophages. c. it activates macrophages. d. it activates lymphocytes.