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 pairing is incorrect, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Identify the first pair: Erythropoietin with Peptide Hormone**
- Erythropoietin is a hormone produced in the kidneys that stimulates the production of red blood cells (RBCs).
- It is classified as a peptide hormone because it is made up of amino acids.
- **Conclusion**: This pairing is correct.

2. **Identify the second pair: Gastrin with Stimulates the secretion of HCl**
- Gastrin is a hormone secreted by G-cells in the stomach.
- Its primary function is to stimulate the secretion of gastric acid (HCl) from parietal cells in the stomach.
- **Conclusion**: This pairing is correct.

3. **Identify the third pair: Cortisol with Steroid**
- Cortisol is a steroid hormone produced by the adrenal glands.
- It plays a role in regulating metabolism, responding to stress, and maintaining blood sugar levels.
- **Conclusion**: This pairing is correct.

4. **Identify the fourth pair: Calcium with Primary Messenger**
- Calcium is often involved in cellular signaling.
- However, it is not classified as a primary messenger; instead, it acts as a secondary messenger in signal transduction pathways.
- **Conclusion**: This pairing is incorrect.

### Final Conclusion:
The incorrect pairing is **Calcium with Primary Messenger**.