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Giardia lamblia is an intestinal parasite of humans and other mammals that causes intestinal ailments in most people who ingest the cysts. Upon ingestion, each cyst releases two motile cells, called trophozoites. These attach to the small intestine's lining via a ventral adhesive disk. The trophozoites anaerobically metabolize glucose from the host's intestinal contents to produce ATP. Reproduction is completely asexual, occurring by longitudinal binary fission of trophozoites, with each daughter cell receiving two haploid nuclei (n = 5). A trophozoite will often encyst as it passes into the large intestine by secreting around itself a case that is resistant to cold, heat, and dehydration. Infection usually occurs by drinking untreated water that contains cysts.
-Giardia's mitosome can be said to be "doubly degenerate," because it is a degenerate form of a ________, an organelle that is itself a degenerate form of a(n)________.
A)nucleus; archaean
B)nucleus; bacterium
C)mitochondrion; proteobacterium
D)mitochondrion; spirochete
E)chloroplast; cyanobacterium

Question

Quizplus · Accepted Answer

Giardia lamblia has a mitosome that is doubly degenerate, which means it is a degenerate form of a degenerate organelle. The mitosome is a reduced form of a mitochondrion, and it is degenerate because it lacks the electron transport chain and cannot produce ATP. The mitochondrion itself was derived from an endosymbiotic event involving a proteobacterium.

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