What are the characteristic morphological features of Giardia lamblia trophozoites and cysts?

• A. Trophozoites are pear-shaped with two nuclei and flagella; cysts are oval with four nuclei and median bodies
• B. Trophozoites are spherical with one nucleus; cysts are elongated with two nuclei
• C. Trophozoites are amoeboid; cysts are spherical with no nuclei
• D. Trophozoites are rod-shaped; cysts are irregular with three nuclei

Answer: (A)

Giardia lamblia has two forms in its life cycle that are distinguished by specific shapes and nuclear content. The trophozoite is pear-shaped, motile, and contains two nuclei with multiple flagella, giving it a characteristic appearance in the intestinal lumen. The cyst, which is the environmentally resistant form, is oval or ellipsoidal and features a thick wall with four nuclei and median bodies inside.

This combination—pear-shaped trophozoite with two nuclei and flagella, and an oval cyst with four nuclei and median bodies—fits the known morphology of Giardia lamblia and is the best description of its two stages. Other options describe shapes or nuclear counts that do not match Giardia’s documented features, such as spherical or amoeboid trophozoites, or cysts with the wrong number of nuclei.