Identifying blood cells by size and nucleus shape

Steps:

• Examine cell sizes: the largest cell is a monocyte, the smaller round-nucleus cell is a lymphocyte.
• Monocytes have a kidney-shaped nucleus and are 12-20 μm in diameter.
• Lymphocytes have a round nucleus and are 7-15 μm in diameter.
• Match labels: Z is the large cell with irregular nucleus (monocyte), Y is the small cell with round nucleus (lymphocyte).

Why B is correct:

• Monocytes are the largest white blood cells with indented nuclei, matching Z's size and shape per standard hematology definitions.

Why the others are wrong:

• A misidentifies the monocyte as Y (too small).
• C mislabels the small Y as monocyte and large Z as lymphocyte.
• D mislabels the large Z as lymphocyte (lymphocytes are smaller).

Final answer: B