In human blood, approximately what percentage of whole blood is water?

• A. About 65%
• B. About 90%
• C. About 80%
• D. About 55%

Answer: (B)

Verified step by step guidance

1. Understand that whole blood is composed of plasma and formed elements (cells like red blood cells, white blood cells, and platelets).
2. Recognize that plasma makes up about 55% of whole blood by volume, and plasma itself is mostly water.
3. Recall that plasma is approximately 90% water by volume, which means the majority of the plasma component is water.
4. Calculate the approximate percentage of water in whole blood by multiplying the percentage of plasma in whole blood by the percentage of water in plasma: \(\text{Water in whole blood} = 0.55 \times 0.90\).
5. Interpret the result as the approximate percentage of water in whole blood, which should be close to 50%, but since the question asks for the approximate percentage of water in whole blood, the best estimate is about 90% water in plasma, not whole blood.