In which one of the following pair of terms both represent one and same thing?

Options

A. plasma-Serum
B. atria-ventricular node-Pacemaker
C. leucocytes Lymphocytes
D. mitral valve-Bicuspid valve

Explanation

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

### Step-by-Step Solution:

1. **Option 1: Plasma and Serum**
- **Plasma** is the liquid component of blood that contains water, electrolytes, proteins (including fibrinogen), hormones, and waste products. It is the medium in which blood cells (RBCs, WBCs, platelets) are suspended.
- **Serum** is the fluid that remains after blood has clotted, meaning it is plasma without the clotting factors (like fibrinogen) and blood cells.
- **Conclusion**: Plasma and serum are not the same; they have different compositions.

2. **Option 2: Atrioventricular Node and Pacemaker**
- The **Atrioventricular (AV) Node** is a part of the heart's electrical conduction system, located between the atria and ventricles, and helps regulate the heartbeat.
- A **Pacemaker** is an artificial device implanted in the heart to control abnormal heart rhythms (arrhythmias).
- **Conclusion**: The AV node is a natural part of the heart, while a pacemaker is an artificial device. They do not represent the same thing.

3. **Option 3: Leukocytes and Lymphocytes**
- **Leukocytes** are a broad category of white blood cells (WBCs) that play various roles in the immune system.
- **Lymphocytes** are a specific type of leukocyte that is primarily involved in the immune response.
- **Conclusion**: While lymphocytes are a type of leukocyte, the terms are not synonymous. They represent different scopes of white blood cells.

4. **Option 4: Mitral Valve and Bicuspid Valve**
- The **Mitral Valve** is located between the left atrium and left ventricle of the heart and regulates blood flow from the atrium to the ventricle.
- The **Bicuspid Valve** refers to the same valve, named for its two cusps (flaps).
- **Conclusion**: Mitral valve and bicuspid valve are two names for the same structure in the heart.

### Final Answer:
The correct pair of terms that represent the same thing is **Mitral Valve and Bicuspid Valve**.

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