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 needed for vigorous vegetative leaf and stem growth and dark green leaf color (chlorophyll production). It feeds soil microorganisms as they decompose organic matter. It is part of proteins, enzymes, chlorophyll, and growth regulators. Deficiency Symptoms General: Stunted growth and shorter internodes, small pale yellow leaves.