Question

the figure shows a path model of the homeostatic system that regulates the concentration of calcium ions (\\(\text{ca}^{2+}\\)) in blood. this regulated variable is represented by a dashed box. other variables are represented by a solid black box. an arrow connecting one box to another indicates a relationship between two variables. the sign above an arrow (+ or -) indicates whether the variables are positively or negatively related.

note: this information is repeated for questions 2 through 4.

which variable depends directly on the rate at which osteoblasts absorb calcium ions (\\(\text{ca}^{2+}\\))?

a. the concentration of \\(\text{ca}^{2+}\\) in a parafollicular cell
b. the concentration of calcitonin in blood
c. the concentration of \\(\text{ca}^{2+}\\) in blood
d. i do not know the answer.

Explanation:

Identify the source variable in the question

The question asks which variable depends directly on the "Rate at which osteoblasts absorb \(Ca^{2+}\)". In causal diagrams, if variable B depends directly on variable A, there must be a direct arrow pointing from A to B.

Trace the outgoing arrow from the source variable

Using the Path Models and Causal Diagrams knowledge points:

$$ \text{Rate at which osteoblasts absorb } Ca^{2+} \xrightarrow{\quad-\quad} \text{Concentration of } Ca^{2+} \text{ in blood} $$

The arrow originating from the box "Rate at which osteoblasts absorb \(Ca^{2+}\)" points directly to the dashed box "Concentration of \(Ca^{2+}\) in blood" with a negative sign. Therefore, the concentration of \(Ca^{2+}\) in blood depends directly on this rate.

Answer:

• a. the concentration of \(Ca^{2+}\) in a parafollicular cell
• b. the concentration of calcitonin in blood
• c. the concentration of \(Ca^{2+}\) in blood (Correct answer)
• d. I do not know the answer.