Final answer:
Leukocytes, or white blood cells (WBC), vary in number per drop of blood between species and are part of the immune system. In humans, the healthy leukocyte count ranges from 3.5 to 11 x 10⁹ cells/L, with the specific types of WBCs including granulocytes and agranulocytes, each playing unique roles in immunity.
Step-by-step explanation:
The question pertains to the number of white blood cells (WBC), also known as leukocytes, found in a drop of blood. Leukocytes are an essential part of the immune system, with their primary function being to defend the body against invading microorganisms and other potential threats. The absolute number of leukocytes in the blood is measured in cells per microliter (µl), and this can vary significantly between species. For example, primates typically have a leukocyte count ranging from 4,800 to 10,800 cells per µl, while dogs can range from 5,600 to 19,200 cells per µl, cats from 8,000 to 25,000 cells per µl, cattle from 4,000 to 12,000 cells per µl, and pigs from 11,000 to 22,000 cells per µl.
In humans, a healthy leukocyte count is generally considered to be between 3.5 to 11 x 10⁹ cells/L. There are different types of WBCs, including granulocytes (which contain visible granules) such as neutrophils, eosinophils, and basophils, and agranulocytes (which do not contain granules) such as lymphocytes and monocytes, each with specific functions within the immune system. A single drop of human blood contains not only millions of leukocytes but also millions of red blood cells and platelets.