Final answer:
The expected reference range for a WBC count in humans is between 4.5 and 11.0 x 10^3/μL, with white blood cells playing a critical role in the body's immune defense system.
Step-by-step explanation:
The expected reference range for a WBC (white blood cell) count is a) 4.5-11.0 x 103/μL. This is the normal range for humans, with values outside this range potentially indicating an infection or other medical conditions. White blood cells are an essential part of the immune system, defending the body against invading pathogens and removing abnormal cells. The number of white blood cells in the blood can vary based on age, gender, and overall health. An increase or decrease in the WBC count can provide important diagnostic information for conditions such as infections, inflammation, and immune system disorders.