What is the main function of white blood corpuscles (WBCs) in the human body?

Introduction / Context:
Blood is made up of plasma and different types of blood cells, each performing specialised functions. The three main cellular components are red blood cells, white blood cells, and platelets. Understanding the primary role of white blood corpuscles (WBCs) is fundamental in biology and medicine. This question asks what the main function of WBCs is in the human body.

Given Data / Assumptions:

• WBCs are also called leukocytes.
• The options include transport of carbon dioxide, transport of oxygen, providing defence and immunity, none of these, and initiation of blood clotting.
• Red blood cells and platelets handle other major tasks like gas transport and clotting.
• We assume normal human physiology without disease.

Concept / Approach:
White blood cells are the soldiers of the body's defence system. They identify and destroy invading pathogens such as bacteria, viruses, and parasites, and they also remove damaged and dead cells. Different types of WBCs (neutrophils, lymphocytes, monocytes, eosinophils, basophils) have specialised roles in both innate and adaptive immunity. Red blood cells (erythrocytes) transport oxygen and much of the carbon dioxide, while platelets are primarily responsible for blood clotting. Therefore, the main function of WBCs is to provide defence and immunity to the body.

Step-by-Step Solution:
Step 1: Recall the roles of each blood cell type: RBCs, WBCs, and platelets.Step 2: Recognise that RBCs carry oxygen from the lungs to tissues and transport some carbon dioxide back to the lungs.Step 3: Understand that platelets (thrombocytes) are central to blood clotting and wound sealing.Step 4: WBCs attack pathogens, produce antibodies, and coordinate immune responses.Step 5: Therefore, the option stating To provide defence and immunity to the body correctly summarises the role of white blood corpuscles.

Verification / Alternative check:
Textbooks on human physiology and immunology explain that WBCs form the core of the body's immune system. For example, neutrophils perform phagocytosis, lymphocytes produce antibodies and mediate cellular immunity, and monocytes develop into macrophages that clean up debris. In contrast, RBCs are consistently described as the primary oxygen carriers, and platelets as the clotting elements. This consistent description across sources verifies that immunity and defence is the central function of WBCs.

Why Other Options Are Wrong:
Transport of carbon dioxide is mainly a function of RBCs and plasma, not WBCs.Transport of oxygen is almost entirely carried out by haemoglobin within RBCs.None of these is incorrect because one of the options (defence and immunity) clearly matches WBC function.Initiation of blood clotting is largely the role of platelets and clotting factors, not WBCs.

Common Pitfalls:
Students sometimes confuse the functions of different blood cells or assume that all cells play equal roles in transport and defence. Another mistake is to pick None of these when uncertain, even though one option is clearly correct. To avoid such errors, remember: RBCs for transport of gases, WBCs for immunity, and platelets for clotting.

Final Answer:
The correct answer is: To provide defence and immunity to the body.