Assertion: Aldosterone is a steroid hormone and is important in the control of sodium and potassium ion concentration in mammals. 
Reason: It upgrades sodium ioh concentration in the ECF by promoting reabsorption of sodium ions from renal tubules and excretion of potassium ions in urine

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Assertion**: The assertion states that "Aldosterone is a steroid hormone and is important in the control of sodium and potassium ion concentration in mammals."
- **Explanation**: Aldosterone is indeed a steroid hormone, derived from cholesterol, and plays a crucial role in regulating the balance of sodium (Na+) and potassium (K+) ions in the body.

2. **Understanding the Reason**: The reason provided is that "It upgrades sodium ion concentration in the ECF by promoting reabsorption of sodium ions from renal tubules and excretion of potassium ions in urine."
- **Explanation**: Aldosterone acts on the distal convoluted tubules of the kidneys, where it promotes the reabsorption of sodium ions back into the bloodstream and facilitates the excretion of potassium ions into the urine. This mechanism increases sodium ion concentration in the extracellular fluid (ECF).

3. **Evaluating the Relationship**: Now, we need to evaluate whether the reason correctly explains the assertion.
- **Explanation**: Since the reason accurately describes the function of aldosterone in relation to sodium and potassium ion balance, it serves as a correct explanation for the assertion.

4. **Conclusion**: Both the assertion and the reason are true, and the reason correctly explains the assertion.
- **Final Answer**: Therefore, the correct option is that both assertion and reason are true, and the reason is the correct explanation of the assertion.

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