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.
Root nodule symbiosis enables nitrogenâfixing bacteria to convert atmospheric nitrogen into a form that is directly available for plant growth. Biological nitrogen fixation provides a builtâin supply of nitrogen fertiliser for many legume crops such as peas, beans and clover.