Unlike erythrocytes, leukocytes:

Unlike erythrocytes, leukocytes have multiple types, which is the key distinguishing characteristic addressed here. The white blood cell population is divided into two broad classes — granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (monocytes and lymphocytes) — each with specialized immune functions. Erythrocytes, by contrast, are a single, homogeneous population of cells all dedicated to oxygen transport. The option stating that leukocytes remain in vessels is incorrect; a defining feature of leukocytes is their ability to perform diapedesis, migrating out of blood vessels into tissues to combat infection and inflammation. The option suggesting leukocytes lack organelles applies to mature erythrocytes, not leukocytes; erythrocytes eject their nuclei and most organelles during maturation so they can maximize hemoglobin content, whereas leukocytes retain nuclei and organelles to carry out complex immunological tasks. The option claiming leukocytes are more abundant is also wrong; erythrocytes vastly outnumber leukocytes in normal blood, with roughly 5 million red cells per microliter compared to only 4,000 to 11,000 white cells per microliter. Knowing the diversity of leukocyte types and their respective roles is foundational to understanding immune responses in pathophysiology.