Concept:Calcium is a structural nutrient in plants, mainly required for building and strengthening the cell wall.
Explanation:In plant cells, calcium combines with pectin to form calcium pectate.
This compound is a major component of the middle lamella, which cements neighbouring cells together.
Hence, calcium contributes to mechanical support and cell wall integrity.
It is not used in the formation of ribosomes, proteins, or the cell membrane.
Ribosomes are composed of RNA and proteins, proteins are built from amino acids, and membranes are made of lipids and proteins.
So, among the listed options, calcium is specifically associated with cell wall formation.
Answer:A. cell wall