In which one of the following pairs, two terms represent the same thing ?

Options

A. `"Lymphocyte - erythrocyte"`
B. `"Plasma - serum"`
C. `"Mitral valve - bicuspid valve"`
D. `"Atrioventricular node - pacemaker"`

Explanation

To determine which pair of terms represents the same thing, we need to analyze each pair provided in the question.

### Step-by-Step Solution:

1. **Identify the First Pair: Lymphocytes and Erythrocytes**
- Lymphocytes are a type of white blood cell (WBC).
- Erythrocytes are red blood cells (RBC).
- Conclusion: Lymphocytes and erythrocytes are not the same.

2. **Identify the Second Pair: Plasma and Serum**
- Plasma is the liquid component of blood that contains clotting factors.
- Serum is the liquid that remains after blood has clotted, lacking clotting factors.
- Conclusion: Plasma and serum are not the same.

3. **Identify the Third Pair: Mitral Valve and Bicuspid Valve**
- The mitral valve is also known as the bicuspid valve.
- Both terms refer to the same structure in the heart, which has two flaps and separates the left atrium from the left ventricle.
- Conclusion: Mitral valve and bicuspid valve are the same.

4. **Identify the Fourth Pair: Atrioventricular Node and Pacemaker**
- The atrioventricular (AV) node is a part of the heart's electrical conduction system but is not the primary pacemaker.
- The sinoatrial (SA) node is the actual pacemaker of the heart.
- Conclusion: Atrioventricular node and pacemaker are not the same.

### Final Conclusion:
The only pair where both terms represent the same thing is **Mitral Valve and Bicuspid Valve**.