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.
All plants need nitrogen to grow. They use nitrogen to synthesize DNA, RNA, enzymes and other proteins necessary for growth and reproduction. Both urea and ammonium-based fertilizers contain large amounts of nitrogen that help plants perform to their greatest potential. They are often used in industrial agriculture settings but are also suitable for use in home gardens and landscapes.