in biology, any chemical element required by living organisms in minute amounts, usually as part of a vital enzyme, a cell-produced catalytic protein. Exact needs vary among species, but commonly required plant micronutrients include copper, boron, zinc, manganese, and molybdenum. Animals also require manganese, iodine, and cobalt. Lack of a necessary plant micronutrient in the soil causes plant deficiency diseases; lack of animal micronutrients in the soil may not harm the plants, but, without them, animals feeding solely on those plants develop deficiency diseases.