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 Fertilizer? A good organic nitrogen fertilizer should be added to the soil whenever you plant heavy-feeding vegetables like tomatoes, peppers, chiles, eggplants, cucumbers, squash, melons, or cruciferous vegetables like broccoli, cabbage, and cauliflower. Leafy vegetables like lettuce and spinach also benefit from high levels of nitrogen in the soil.