Final answer:
A monocyte could be easily confused with a lymphocyte due to their similar appearances under a microscope. Both are types of leukocytes but they arise from different stem cell lines, and differences in size and nucleus-to-cytoplasm ratio must be observed to distinguish them correctly.
Step-by-step explanation:
In the identification of peripheral blood-formed elements, a monocyte could be easily confused and misidentified as a lymphocyte due to their similar morphology. Monocytes are types of agranular leukocytes of the myeloid stem cell line that circulate in the bloodstream. While lymphocytes are the only formed elements of blood that arise from lymphoid stem cells and include B cells, T cells, and natural killer cells. Monocytes and lymphocytes have considerable similarity in their appearances, particularly when observed under a microscope without proper differentiation techniques, such as fluorescence-activated cell sorting (FACS). Monocytes are larger than lymphocytes with a more vesicular nucleus and a greater amount of cytoplasm, but without careful observation, these differences can be subtle and lead to misidentification.