Which of the following shows incorrect pairing?

Options

A. Erythropoietin : peptide hormone
B. Gastrin : stimulates the secretion of HCL
C. Steroid : cortisol
D. Primary messenger : calcium ion

Answer

To solve the question of which option shows incorrect pairing, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Option A: Erythropoietin - Peptide Hormone**
- Erythropoietin is indeed a peptide hormone produced by the kidneys. Its primary function is to stimulate the production of red blood cells (RBCs) in the bone marrow.
- **Conclusion:** This pairing is correct.

2. **Option B: Gastrin - Stimulates the secretion of HCl**
- Gastrin is a hormone produced by G-cells in the pyloric region of the stomach. It stimulates the parietal cells to secrete hydrochloric acid (HCl), which is essential for digestion.
- **Conclusion:** This pairing is correct.

3. **Option C: Steroid - Cortisol**
- Cortisol is a steroid hormone produced by the adrenal glands. It plays a crucial role in regulating metabolism, immune response, and stress response.
- **Conclusion:** This pairing is correct.

4. **Option D: Primary Messenger - Calcium Ion**
- Calcium ions (Ca²⁺) are often referred to as secondary messengers in cellular signaling pathways. They play a role in transmitting signals from receptors to target molecules within the cell, but they are not classified as primary messengers.
- **Conclusion:** This pairing is incorrect.

### Final Answer:
The option that shows incorrect pairing is **D: Primary messenger - Calcium Ion**.

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