Living organisms require at least 27 elements of which 15 are metals. Among these, those required in major quantities include

Living organisms require a suite of elements, but the metals needed in relatively large (macromineral) amounts are the four main-group alkali and alkaline-earth cations: potassium, sodium, magnesium and calcium. Textbook listings identify calcium, potassium and magnesium among the significant nutrients in living matter [1], and reviews of essential metals explicitly treat sodium, potassium, magnesium and calcium as the primary main-group elements required in larger quantities for biological function [2]. Other metal elements such as manganese, molybdenum and copper are important biologically but are classed as minor/trace elements required in much smaller amounts [3], so they are not part of the “major quantities” group.

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Carbon and Oxygen Cycles > p. 19
2. [2] https://www.sciencedirect.com/science/article/pii/S0009279722003787
3. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > z. Micronutrientsl > p. 363