Final answer:
A large leukocyte with a U-shaped nucleus and no visible granules is indicative of a monocyte, which is an agranular leukocyte.
Step-by-step explanation:
Identifying Leukocytes Through a Microscope
When observing a leukocyte through a microscope, identifying its characteristics such as the presence of granules and the shape of its nucleus is crucial in determining its type. A large leukocyte with a U-shaped nucleus and no visible granules is characteristic of a monocyte. Monocytes are part of the agranular leukocytes category and are known for their phagocytic abilities as they mature into macrophages. In contrast, neutrophils, which are granular leukocytes, have a nucleus with two to five lobes and light lilac-stained granules. Basophils, another type of granular leukocytes, contain large granules that stain dark blue and typically have a two-lobed nucleus. Consequently, the leukocyte observed is most likely a monocyte.