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 [c1]. White blood cells, also known as leukocytes, are the primary components responsible for the body's defense and immune response [t2][t3]. Their main function is to fight infections by defending the body against bacteria, viruses, and other foreign invaders [t5][t6]. They achieve this through various mechanisms, such as lymphocytes producing antibodies or T cells directly attacking infected cells [t9]. In contrast, red blood cells (erythrocytes) contain hemoglobin, which is specialized for transporting oxygen from the lungs to tissues [c3][t1]. Platelets (thrombocytes) are cell fragments that facilitate blood clotting at sites of injury to prevent excessive bleeding [c2][t9]. Therefore, white blood cells are the specific part of blood dedicated to the function of body defense [t7][t8].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.7 > p. 91
2. [2] https://www.ncbi.nlm.nih.gov/books/NBK607436/
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Do You Know? > p. 90
4. [4] https://www.ncbi.nlm.nih.gov/books/NBK279392/