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.
Other examples of nitrogen-fixing plants that are well-known thanks to their use in agriculture include: 1  Vetch (Vicia spp.) 2  Alfalfa (Medicago sativa) 3  Peas (Pisum sativum)  Beans (Phaseolus spp.)