12. a. why is nitrogen necessary for life? include the terms amino acids and proteins in your answer.

b. oxygen combines with nitrogen to form what types of chemicals that are used by plants?
c. why is phosphorus necessary for life?
d. phosphorus combines with oxygen to form what types of chemicals that are used by plants?
e. what does the polar nature of water molecules have to do with substances being able to dissolve in water?
f. why is the ability of substances to dissolve in water important for plants?