Which of the following parts of blood carry out the function of body defence ?

Blood is a fluid connective tissue composed of plasma and various specialized cells. White blood cells, also known as leukocytes, are the primary components responsible for the body's defense and immune response [t1][t8]. They protect the body by fighting infections, attacking bacteria, viruses, and other foreign microbes, and launching immune attacks against cancer cells [t1][t3][t7]. In contrast, red blood cells (erythrocytes) contain the respiratory pigment haemoglobin, which is specialized for transporting oxygen from the lungs to tissues and carrying carbon dioxide back for exhalation [c1][c3][t4]. Platelets (thrombocytes) are responsible for blood clotting and plugging leaks at sites of injury to prevent excessive blood loss [c2][t1]. Therefore, while all components are vital for survival, only white blood cells carry out the specific function of body defense [t2][t5].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.7 > p. 91
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Maintenance by platelets > p. 94
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Do You Know? > p. 90
4. [4] https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/immune-system