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.
1 To get the best head start, turn over your pea planting beds in the fall, add manure to the soil, and mulch well.  As with other legumes, pea roots will fix nitrogen in the soil, making it available for other plants.