Which of the following best describes the primary function of Ca^{2+} in biological systems?

• A. It serves as a major energy carrier in cells.
• B. It acts as a signaling ion involved in muscle contraction and neurotransmission.
• C. It is the main component of nucleic acids.
• D. It functions as a reducing agent in metabolic reactions.

Answer: (B)

Verified step by step guidance

1. Identify the role of Ca^{2+} ions in biological systems by recalling their common functions in cellular processes.
2. Recall that Ca^{2+} ions are not involved in energy storage or transfer like ATP, so they do not serve as major energy carriers in cells.
3. Understand that Ca^{2+} ions are not structural components of nucleic acids, which are primarily composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus atoms.
4. Recognize that Ca^{2+} ions do not act as reducing agents; reducing agents typically donate electrons in metabolic reactions, which is not a role of calcium ions.
5. Conclude that the primary function of Ca^{2+} in biological systems is to act as a signaling ion, playing a crucial role in processes such as muscle contraction and neurotransmission.