In human blood, which component makes up the greatest proportion by volume?

• A. Plasma
• B. Leukocytes (white blood cells)
• C. Erythrocytes (red blood cells)
• D. Platelets (thrombocytes)

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the components of human blood. Blood is composed of plasma and formed elements, which include erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (thrombocytes).
2. Step 2: Recall the approximate volume percentages of each component in blood. Plasma typically makes up about 55% of blood volume, erythrocytes about 40-45%, leukocytes and platelets together less than 1%.
3. Step 3: Recognize that plasma is the liquid portion of blood, consisting mostly of water, proteins, nutrients, hormones, and waste products, which allows it to occupy the largest volume fraction.
4. Step 4: Compare the volume proportions of each component to identify which one is the greatest by volume. Since plasma is over half of the blood volume, it is the component with the greatest proportion.
5. Step 5: Conclude that plasma is the correct answer because it makes up the greatest proportion of blood volume compared to erythrocytes, leukocytes, and platelets.