Name one useful substance transported by blood.

Answer

**Step-by-Step Solution:**

1. **Understanding Blood Composition**: Blood is a special type of connective tissue that consists of a liquid part called plasma and formed elements. Plasma makes up about 55% of blood, while formed elements account for about 45%.

2. **Identifying Formed Elements**: The formed elements in blood include white blood cells (WBC), red blood cells (RBC), and platelets. Each of these components has a specific function.

3. **Focusing on Red Blood Cells**: Among the formed elements, red blood cells (RBCs) are the most abundant. They contain a red-colored iron-containing protein called hemoglobin.

4. **Function of Hemoglobin**: Hemoglobin is crucial because it binds with oxygen. This means that the primary function of RBCs is to transport oxygen throughout the body.

5. **Conclusion**: Therefore, one useful substance transported by blood is oxygen, and it is transported by red blood cells.

**Final Answer**: One useful substance transported by blood is oxygen, and it is transported by red blood cells (RBCs).

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