Calcium is an essential element in living organisms. It plays an important role in the metabolism of nitrogen in some plants where a deficiency of calcium leads to poor absorption of nitr ogen. Lack of calcium in plant nutrition leads to a reduction in the number and size of the chloroplasts.

Calcium is the most abundant inorganic element in the higher animals and is located principally in the bones and teeth as apatite, a calcium phosphate mineral. Blood is also a huge reservoir of calcium in animals. Calcium is distributed throughout all tissues where it has special roles in controllin g nerve impulse transmission, muscle action, blood clotting and cell permeability.

Calcium deficiency is exhibited by the onset of rickets, failure of the blood-clotting mechanism, nervous disorder and convulsive muscular contractions. Vitamin D greatly improves the absorbability of calcium ion and the value of this vitamin in treat ing rickets is based in part on this effect.

Large intakes of calcium lead to excessive calcification and kidney stones.