Which of the following cycles is crucial to living organisms? a. phosphorus b. water c. carbon d. all of the above

The correct answer is d. all of the above.

The cycling of essential elements of living organism throughout the ecosystem is referred to as biogeochemical cycles. For example, carbon cycle, water cycle, phosphorus cycle, nitrogen cycle, etc.

All these cycles are essential for the survival of the living organisms. They play important role in life processes (such as metabolism, action potential etc) as well as form the basis of structure.

For example carbon, nitrogen, hydrogen, phosphorus, water are the basic elements used in the formation of DNA, RNA, amino acids etc.  

carbon atoms, hydrogen, oxygen, and nitrogen.