Which of the following statements best describes the relationship between homeostasis and function with the appropriate electrolyte in the human body?
A) Homeostasis of calcium is crucial for nerve function and muscle contraction.
B) Homeostasis of potassium is primarily responsible for the formation of bones and teeth.
C) Homeostasis of sodium is unnecessary for maintaining fluid balance and blood pressure.
D) Homeostasis of chloride does not affect acid-base balance in the body.

Calcium serves many functions within the body. Aside from being the building blocks of our bones, calcium ions are also responsible for depolarizing neurons. Normally, neurons have slight electrical charge around -70 mV. In order to fire, neurons have to raise their electrical charge up to -55 mV, triggering a chain reaction that results in the electrical charge of the neuron becoming positive.

Calcium ions are positive, and are thus responsible for raising the electrical charge within a neuron by entering it. Since neurons also control voluntary muscle movement and function, calcium ions are also indirectly involved in aiding muscle contractions. Thus, homeostasis of calcium is necessary to maintain muscle and neuronal function within the body.

Choice B is incorrect because calcium is the main electrolyte responsible for bone and teeth formation. On the other hand, potassium's main role is to also aid in neuron function (since potassium ions also regulate electrical charge) and the aid in the movement of nutrients and waste.

Choice C is incorrect because sodium is absolutely necessary for maintaining fluid balance and blood pressure. Sodium levels can change the solute concentration of solutions, altering the level and direction of osmosis. Sodium's concentration can affect the amount of water entering and leaving our cells, and it also affects blood pressure through controlling the viscosity of blood solute content.

Choice D is incorrect because chloride does indeed affect acid-base balance (otherwise known as pH levels) in the body. Chlorine usually exists in the body as sodium chloride (edible salt) or hydrochloric acid (HCl). Both of these compounds can affect pH levels in the blood since both HCl and NaCl can lower pH levels.