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.
In Thailand, pigeon peas are grown as a host for scale insects which produce lac, the key ingredient in shellac. Pigeon peas are in some areas an important crop for green manure, providing up to 90 kg nitrogen per hectare (Adu-Gyamfi et al., 2007) .