The classic form of Blastocystis hominis has which characteristic?

• A. Central body occupying up to 90% of the cell
• B. Nuclei arranged in a ring
• C. Presence of an undulating membrane
• D. No central body

Answer: (A)

Morphology of Blastocystis hominis in its classic form is defined by a large central vacuole that dominates the cell. In this vacuolar form, the central body can occupy up to about 90% of the cell, leaving only a thin rim of cytoplasm around it. The nucleus is pulled toward the periphery, giving the appearance of a cell with a thin cytoplasmic edge encircling a large central vacuole. This distinctive large central vacuole is what most clearly identifies the classic form. Other features like an undulating membrane are not characteristic of this form, and a lack of a central body would not fit the classic vacuolar appearance.