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.
Nitrogen is one of primary macronutrients that plants need for survival, aside from phosphorus and potassium. It is important for plant growth and development, particularly in metabolic processes such as production of nucleic acids, proteins, and other helper molecules.