Explain in brief about  the term - Calcium  

Calcium is absorbed as Ca²⁺ ion and is a constituent of cell wall, an activator of different plant enzymes and is essential for the stability of cell membranes. The specific physiological functions performed by calcium in plants are not clearly defined. It is considered to be essential to the formation of the middle lamellae of cells because of its alleged role in the synthesis of calcium pectate. It has also been suggested that calcium favours the formation of protein and increases the protein content of mitochondria. Since it is a constituent of the cell wall, it therefore helps in increasing stiffness of straw. It acts to neutralise organic acids and thus acts as a detoxifying agent. It also encourages seed production.