Carboxyl groups have an electronegative oxygen atom double bonded to a carbon atom. This carbon-oxygen bond is very polar and the fact that its a double bond increases the polarity of the bond.
PEA agar, also referred to as Phenylethyl Alcohol Agar is a medium  used by microbiologists to grow microorganisms. The ingredient that  supplies nitrogen is casein. Making the world better, one answer at a time.
Fertilizer Ingredients. Apple trees require nitrogen, phosphorus and potassium -- the three numbers on fertilizer bags -- as well as various trace minerals. For home growers, fertilizers should have a higher nitrogen ratio to fuel healthy growth. Common granular 20-10-10 fertilizer is suitable for apples.