Biological Systems MCAT Practice Exam

Which type of white blood cell is most abundant and primarily involved in phagocytosis?

1. Macrophages

2. Lymphocytes

3. Neutrophils

4. Eosinophils

The correct answer is: Neutrophils

Neutrophils are the most abundant type of white blood cells in the human body, accounting for approximately 50-70% of all leukocytes. Their primary function centers around phagocytosis, which is the process of engulfing and digesting foreign particles such as bacteria and fungi. Neutrophils respond quickly to sites of infection or inflammation and are one of the first immune cells to arrive at the scene. During an immune response, neutrophils use various mechanisms to recognize and eliminate pathogens. They have numerous receptors on their surface that allow them to detect and bind to pathogens effectively. Once engaged, neutrophils engulf these microorganisms and utilize enzymes contained within their granules to break them down, effectively clearing infections from the body. In contrast, macrophages are also involved in phagocytosis but are generally less abundant than neutrophils and may arrive later in the immune response. Lymphocytes, which include T cells and B cells, play key roles in the adaptive immune response but are not primarily phagocytic. Eosinophils are mainly involved in combatting parasitic infections and in allergic reactions but also do not specialize in phagocytosis to the extent that neutrophils do. Thus, neutrophils