Which one among the following parts of blood carries out the function of body defence?

Blood is a fluid connective tissue composed of plasma and various specialized cells, each performing distinct physiological roles. White blood cells, also known as leukocytes, are the primary components responsible for the body's defense mechanism [2]. They function as a critical part of the immune system by identifying, attacking, and destroying harmful pathogens such as bacteria, viruses, and germs. In contrast, red blood cells (erythrocytes) and the protein they contain, haemoglobin, are primarily responsible for transporting oxygen from the lungs to tissues and carrying carbon dioxide back for exhalation [1]. Platelets (thrombocytes) are specialized for blood clotting and plugging leaks at sites of injury to prevent excessive blood loss. Therefore, white blood cells are the specific blood component dedicated to fighting infections and maintaining body defense [2].

Sources

1. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Maintenance by platelets > p. 94
2. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Do You Know? > p. 90