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.
Nitrogen can be provided to. native pecans by using fertilizer or by legumes. (Table 2). Cool-season legumes such as a red clover-. white cover mixture can supply some or all the. nitrogen a native pecan tree will need without. competing with the tree for soil moisture and. nutrients during the growing season.