A 15-um pear-shaped flagellate with falling leaf motility is most consistent with which organism?

A 15-um pear-shaped flagellate with falling leaf motility is most consistent with which organism?

• A. Giardia lamblia
• B. Balantidium coli
• C. Chilomastix mesnili
• D. Trichomonas hominis

Answer: (A)

The key idea is recognizing Giardia lamblia by its combination of size, shape, and a distinctive motility pattern. Giardia trophozoites are about 10–15 μm long and pear-shaped, with multiple flagella. Their movement is described as a falling-leaf motion, a smooth, gliding wave produced by coordinated flagellar beating as they swim. That falling-leaf motility is a classic hallmark of Giardia and is the best clue among the options provided. Balantidium coli is a large ciliate, so its locomotion comes from cilia and its cells are much bigger than 15 μm. Chilomastix mesnili is also a flagellate but generally does not exhibit the falling-leaf motility pattern and has different body characteristics. Trichomonas hominis is a smaller flagellate with a different, more jerky or erratic type of movement. The falling-leaf motion is most characteristic of Giardia lamblia, which is why it’s the best match for the described organism.

The key idea is recognizing Giardia lamblia by its combination of size, shape, and a distinctive motility pattern. Giardia trophozoites are about 10–15 μm long and pear-shaped, with multiple flagella. Their movement is described as a falling-leaf motion, a smooth, gliding wave produced by coordinated flagellar beating as they swim. That falling-leaf motility is a classic hallmark of Giardia and is the best clue among the options provided.

Balantidium coli is a large ciliate, so its locomotion comes from cilia and its cells are much bigger than 15 μm. Chilomastix mesnili is also a flagellate but generally does not exhibit the falling-leaf motility pattern and has different body characteristics. Trichomonas hominis is a smaller flagellate with a different, more jerky or erratic type of movement. The falling-leaf motion is most characteristic of Giardia lamblia, which is why it’s the best match for the described organism.