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.
PLANT FOOD AND NUTRIENTS - Cannabis Growing Guide. Plant foods have 3 main ingredients that will be the mainstay of the garden, Nitrogen, Phosphorus, and Potassium. These 3 ingredients are usually listed on the front label of the plant food in the order of N-P-K. A 20-20-20 plant food has a Nitrogen level of 20%. Secondary nutrients are Calcium, Sulphur and Magnesium. In trace quantities, boron, copper, molybenum, zink, iron, and manganese.