White blood cells act

White blood cells, also known as leukocytes, are the primary components of the body's immune system [1]. Their main function is to act as a defense against infection by identifying and destroying foreign invaders such as bacteria, viruses, fungi, and parasites [1]. They circulate in the bloodstream and can move into tissues to locate and attack pathogens. In contrast, other blood components handle different tasks: red blood cells (erythrocytes) are responsible for oxygen transport from the lungs to tissues [2], while platelets are essential for blood clotting at injury sites [1]. White blood cells protect the body by producing antibodies or through phagocytosis, where they engulf and digest harmful microbes and cellular debris [4]. Thus, they function as the body's internal 'army' against disease.

Sources

1. [1] https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/immune-system
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.7 > p. 91
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Maintenance by platelets > p. 94
4. [4] https://www.ncbi.nlm.nih.gov/books/NBK563148/