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.
It is a characteristic component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters and shrimps) and insects, the radulae of molluscs, and the beaks and internal shells of cephalopods, including squid and octopuses.hitin is a modified polysaccharide that contains nitrogen; it is synthesized from units of N-acetylglucosamine (to be precise, 2-(acetylamino)-2-deoxy-. -glucose). These units form covalent Î²-1,4 linkages (similar to the linkages between glucose units forming cellulose).