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.
Typical nitrogen fertilizers used on strawberries include urea (46% N), ammonium nitrate (34% N), potassium nitrate (13% N), and calcium nitrate (15% N). Animal manure may be used as a nitrogen carrier because it also contributes to soil fertility via its phosphorus, potassium, and micro-nutrient content.