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.
The trophozoites of Giardia were first observed in 1681 in the diarrhea stools of the first known person to view protists with a microscope, a person named
A) Robert Koch.B) Robert Hooke.
C) Isaac Newton.
D) van Leeuwenhoek.
E) Louis Pasteur.
Answer: D
Given that Flagyl produces only minor side effects (if any) in humans, and given the set of parasites that it kills, Flagyl's mode of action probably involves
A) peptidoglycan.B) mitochondria or mitosomes.
C) anaerobic metabolic pathways.
D) nuclear envelopes.
E) microtubules.
Answer: C
Giardia's mitosome can be said to be "doubly degenerate," because it is a degenerate form of ________, an organelle that is itself a degenerate form of ________.
A) nucleus; archaean
B) nucleus; bacterium
C) mitochondrion; proteobacterium
D) mitochondrion; spirochete
E) chloroplast; cyanobacterium
Answer: C
The mitosome of Giardia has no DNA within it. If it did contain DNA, then what predictions should we be able to make about its DNA?
1. It is linear.2. It is circular.
3. It has many introns.
4. It has few introns.
5. It is not associated with histone proteins.
6. It is complexed with histone proteins.
A) 1, 3, and 5
B) 1, 4, and 5
C) 2, 3, and 6
D) 2, 4, and 5
E) 2, 4, and 6
Answer: D
Given the putative ancestry of Giardia's mitosome, what should we predict is true of the mitosome? A) It has electron transport systems that use oxygen as the final electron acceptor.
B) It has a double membrane.C) It has thylakoids.
D) It contains microtubules, arranged in the "9 + 2 pattern."
E) It contains 80S (eukaryotic) ribosomes.
Answer: B
Given its mode of reproduction and internal structures, which of the following should be expected to occur in Giardia at some stage of its life cycle?
1. separation (segregation) of daughter chromosomes2. crossing over
3. meiosis
A) 1 only
B) 3 only
C) 1 and 2
D) 1 and 3
E) 2 and 3
Answer: A
Unlike most excavates, Giardia trophozoites have no oral groove and are unable to form food vacuoles. Thus, we should expect its nutrition (mostly glucose) to come from A) its mitosomes.
B) endosymbiotic cyanobacteria.C) the ventral disk by which it adheres to the intestinal lining.
D) osmosis involving aquaporins.
E) plasma membrane proteins that are transporters or pumps.
Answer: E
Diplomonads, such as Giardia, contain two haploid nuclei per trophozoite. Thus, during the G1 phase of the cell cycle, there should be a total of how many unreplicated chromosomes per trophozoite, and during the G2 phase, how many replicated chromosomes per trophozoite? A) 5; 5
B) 5; 10C) 10; 10
D) 10; 20
E) 20; 20
Answer: C
During passage through the large intestine, a trophozoite will often secrete a case around itself, forming a cyst. Cysts contain four haploid nuclei. When cysts "hatch" within a new host, two trophozoites are released. Thus, which of the following must happen within the cyst, prior to hatching?
1. meiosis2. nuclear division
3. S phase
4. binary fission
A) 1 only
B) 1 and 2
C) 2 and 3
D) 2 and 4
E) 2, 3, and 4
Answer: E
The cysts of Giardia are most analogous to the A) mitochondria of ancestral diplomonads.
B) nuclei of archaeans.C) endospores of bacteria.
D) capsids of viruses.
Answer: C
If the mitosomes of Giardia contain no DNA, yet are descendants of what were once free-living organisms, then where are we likely to find the genes that encode their structures, and what accounts for their current location there? A) plasmids; conjugation
B) plasmids; transformationC) nucleus; horizontal gene transfer
D) nucleus; S phase
Answer: C
The primary treatment for giardiasis (infection with Giardia), as well as for trichomoniasis (infection with Trichomonas vaginalis) and for amoebic dysentery (infection with Entamoeba histolytica), is a drug marketed as Flagyl (generic name is metronidazole). The drug also kills anaerobic gut bacteria. Consequently, which of these are cues that Flagyl's mode of action has nothing to do with attacking or disabling the parasites' flagella, as the drug's name might imply? 1. It would also harm the flagellated lining of the human intestine.
2. Entamoeba possesses pseudopods, not flagella, yet it is killed by Flagyl.3. Prokaryotic flagella and eukaryotic flagella are radically different from each other and unlikely to be harmed by the same chemical.
4. Not all anaerobic gut bacteria possess flagella, yet it kills these bacteria.
A) 1 and 2
B) 1 and 3
C) 2 and 3
D) 1, 2, and 4
E) 2, 3, and 4
Answer: E
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