Are a part of cells and intercellular substance (calcium and phosphorus are part of bone tissue); are necessary for the transport of substances into and out of the cell. They are necessary for many physiological and biochemical processes, for example, calcium for blood clotting, sodium and potassium for the work of muscle and nerve cells, iron is part of hemoglobin, iodine is necessary for the work of thyroid hormones.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.