Paulinella chromatophora is one of the few cercozoans that is autotrophic, carrying out aerobic photosynthesis with its two elongated "cyanelles." The cyanelles are contained within vesicles of the host cell, and each is derived from a cyanobacterium, though not the same type of cyanobacterium that gave rise to the chloroplasts of algae and plants.
The closest living relative of P. chromatophora is the heterotroph, P. ovalis. What type of evidence permits biologists to make this claim about relatedness?
A) morphologicalB) ecological
C) biochemical
D) genetic
E) fossil
Answer: D
The closest living relative of P. chromatophora is the heterotroph, P. ovalis. P. ovalis uses threadlike pseudopods to capture its prey, which it digests internally. Which of the following, if observed, would be the best reason for relabeling P. chromatophora as a mixotroph? A) a threadlike pseudopod
B) a pigmented central vacuole, surrounded by a tonoplastC) a vacuole with food inside
D) a secretory vesicle
E) a contractile vacuole
Answer: C
P. chromatophora secretes around itself a test, or case, of plates made of silica. Which of the following is another rhizarian that would be in competition with P. chromatophora for the silica needed to make these plates, assuming limited quantities of silica in the environment? A) radiolarians
B) foraminiferansC) all other amoeboid cells
D) all other rhizaria
E) diatoms
Answer: A
Which of the following represents the true significance of the finding that the cyanelles of P. chromatophora stem from a different type of cyanobacterium than gave rise to chloroplasts? A) This finding indicates that there is a second evolutionary lineage of photosynthetic eukaryotes.
B) This finding represents the first time that primary endosymbiosis has been directly observed.C) This finding is the strongest evidence yet for the theory of endosymbiosis.
D) This finding is an example of the phenomenon known as "serial endosymbiosis."
E) This finding is the first evidence that eukaryotic cells do not necessarily digest prokaryotic cells that manage to gain access to their cytoplasm.
Answer: A
The genome of modern chloroplasts is roughly 50% the size of the genome of the cyanobacterium from which it is thought to have been derived. In comparison, the genome of P. chromatophora's cyanelle is only slightly reduced relative to the size of the genome of the cyanobacterium from which it is thought to have been derived. What is a valid conclusion that can be drawn from this comparison?
A) Lytic phage infections have targeted the chloroplast genome more often than the P. chromatophora genome.
B) P. chromatophora's cyanelle is the result of an evolutionarily recent endosymbiosis.C) The genome of the chloroplast ancestor contained many more introns that could be lost without harm, compared to the cyanelle's genome.
D) All three of the conclusions above are valid.
E) Two of the conclusions above are valid.
Answer: B
If true, which of the following would be most important in determining whether P. chromatophora's cyanelle is still an endosymbiont, or is an organelle, as the term cyanelle implies? A) If P. chromatophora is less fit without its cyanelle than with it.
B) If the cyanelle is less fit without the host cercozoan than with it.C) If there is ongoing metabolic cooperation between the cyanelle and the host cercozoan.
D) If the magnesium-containing porphyrin ring in the cyanelle's chlorophyll molecules is built by the cyanelle, whereas the organic portion of the chlorophyll molecules is built by the host cercozoan.
E) If there has been movement of genes from the cyanelle genome to the nuclear genome, such that these genes are no longer present in the cyanelle genome.
Answer: E
If true, which of the following is the best evidence that the cyanelles are providing nutrition (in other words, calories) to the surrounding cercozoan?
A) If the cyanelle performs aerobic photosynthesis.
B) If the vesicle membrane that surrounds each cyanelle possesses glucose-transport proteins.C) If the cyanelle performs aerobic respiration.
D) If radiolabeled 14CO2 enters the cyanelle and if, subsequently, radiolabeled glucose is present in cercozoan cytosol.
E) If radiolabeled "heavy" water, 2H2O, enters the cyanelle and if, subsequently, radiolabeled oxygen appears in cercozoan cytosol.
Answer: D
A crucial photosynthetic gene of the cyanobacterium that gave rise to the cyanelle is called psaE. This gene is present in the nuclear genome of the cercozoan, but is not in the genome of the cyanelle. This is evidence of A) reciprocal mutations in the cyanelle and nuclear genomes.
B) horizontal gene transfer from bacterium to eukaryotes.C) genetic recombination involving a protist and an archaean.
D) the origin of photosynthesis in protists.
E) transduction by a phage that infects both prokaryotes and eukaryotes.
Answer: B
What must occur for asexual reproduction to be successful in P. chromatophora?
1. mitosis2. S phase
3. meiosis
4. equal distribution of cyanelles during cytokinesis
A) 1 only
B) 1 and 2
C) 1, 2, and 3
D) 1, 2, and 4
E) 2, 3, and 4
Answer: D
Including the membrane of the surrounding vesicle, how many phospholipid (NOT lipopolysaccharide) bilayers should be found around each cyanelle, and which one of these bilayers should have photosystems embedded in it? A) two; innermost
B) two; outermostC) three; innermost
D) three; middle
E) three; outermost
Answer: A
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