What is the primary function of white blood cells in the immune system?

• A. To transport oxygen throughout the body
• B. To produce hormones for metabolic regulation
• C. To store energy in the form of glycogen
• D. To defend the body against pathogens and foreign substances

Answer: (D)

Verified step by step guidance

1. Step 1: Begin by understanding the role of white blood cells (WBCs) in the immune system. White blood cells, also known as leukocytes, are a critical component of the body's defense mechanism.
2. Step 2: Recognize that white blood cells are not involved in transporting oxygen (this is the role of red blood cells, or erythrocytes, which contain hemoglobin).
3. Step 3: Clarify that white blood cells do not produce hormones for metabolic regulation. Hormones are typically produced by endocrine glands such as the thyroid, pancreas, and adrenal glands.
4. Step 4: Note that white blood cells do not store energy in the form of glycogen. Glycogen storage is primarily a function of liver and muscle cells.
5. Step 5: Conclude that the primary function of white blood cells is to defend the body against pathogens (such as bacteria, viruses, and fungi) and foreign substances. They achieve this through various mechanisms, including phagocytosis, antibody production, and signaling other immune cells.