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.
Certain bac-teria called nitrogen-fixing bacteria are the only organisms thatcan combine nitrogen with other chemicals so it can be used byplants. Nitrogen-fixing bacteria live in growths on the roots ofplants such as peas, soybeans, and peanuts, as shown in Figure 8.