Identifying blood cells by microscopic features

Steps:

• Examine cell shape: irregular outline suggests active engulfing capability.
• Check nucleus: large, kidney-shaped or lobed indicates phagocytic type.
• Note size and granularity: medium-large with visible granules fits white blood cell phagocytes.
• Rule out non-nucleated or tiny cells to confirm white blood cell category.

Why A is correct:

• Phagocytes, like neutrophils or monocytes, appear as large cells with irregular, lobed nuclei under light microscopy, enabling pathogen engulfment per cellular immunity definitions.

Why the others are wrong:

• B: Lymphocytes have small, round nuclei nearly filling the cell, lacking phagocytic granules.
• C: Red blood cells are biconcave discs without nuclei, optimized for oxygen transport.
• D: Platelets are tiny, anucleate fragments, not full cells.

Final answer: A