Final answer:
The leukocyte with a bilobulate nucleus is the basophil, known for its distinctive granules that stain dark blue to purple and a typically two-lobed nucleus, differentiating it from neutrophils and eosinophils.
Step-by-step explanation:
The type of leukocyte that has a bilobulate nucleus is the basophil. Basophils are characterized by their large granules that stain dark blue to purple due to basic (alkaline) stains and a nucleus that typically has two lobes. These leukocytes are among the granular leukocytes, which also include neutrophils and eosinophils; however, only the basophils have a predominantly two-lobed nucleus structure, making it unique among the granulocytes.
While basophils are the least common type of leukocyte, comprising less than one percent of the total leukocyte count, they are easily identifiable under a microscope by their distinctive granules and bilobate nucleus appearance. It is important to note that in addition to basophils, other granulocytes like neutrophils and eosinophils also have lobed nuclei, but neutrophils typically have two to five lobes, and eosinophils have two to three lobes. Hence, basophils are best recognized by their two lobed nuclei and dark-staining granules.