Trichoplax adhaerens (Tp) is the only living species in the phylum Placozoa. Individuals are about 1 mm wide and only 27 µm high, are irregularly shaped, and consist of a total of about 2,000 cells, which are diploid (2n = 12). There are four types of cells, none of which are nerve or muscle cells, and none of which have cell walls. They move using cilia, and any "edge" can lead. Tp feeds on marine microbes, mostly unicellular green algae, by crawling atop the algae and trapping it between its ventral surface and the substrate. Enzymes are then secreted onto the algae, and the resulting nutrients are absorbed. Tp sperm cells have never been observed, nor have embryos past the 64-cell (blastula) stage.
If Tp sperm are observed by future researchers, how many chromosomes should be found in a Tp sperm nucleus?
A) 2B) 3
C) 6
D) 12
Answer: C
In how many of the following ways is Tp unlike the typical animal?
1. Tp is multicellular.2. Tp lacks muscle and nerve cells.
3. Tp has cilia.
4. Tp has a different place where digestion of food occurs.
5. Tp lacks cell walls.
A) only one way
B) two ways
C) three ways
D) four ways
E) all five ways
Answer: B
On the basis of information in the previous paragraph, which of these should be able to be observed in Tp?
A) the act of fertilizationB) the process of gastrulation
C) eggs
D) All three of the responses above are correct.
E) Two of the responses above are correct.
Answer: C
In its native environment, a Tp cell neither gains nor loses water. What should one expect to occur when Tp is placed into fresh water?
A) no change from the above, as fresh water is its native environmentB) lysis
C) plasmolysis
D) slight shrinkage
Answer: B
Tp's body symmetry seems to be most like that of A) most sponges.
B) cnidarians.C) worms.
D) tetrapods.
E) Two of the responses above are correct.
Answer: A
In an experiment, several Tp individuals were stained different colors. The stained individuals were then passed through a strainer, disaggregated to the level of single cells, and collected into a common container of seawater. Which subsequent finding would be most surprising if the Tp individuals used in this experiment had been produced by sexual, rather than asexual, means?
A) If all of the cells from a given individual reaggregated to form the same individual, and if each cell had retained its original identity, as far as cell type goes.
B) If all of the cells from a given individual reaggregated to form the same individual, but if each cell had a different identity than it had before disaggregation.C) If cells from different original individuals reaggregated together to form new individual organisms.
D) If cells from different original individuals reaggregated together to form new species.
Answer: C
Learn More :
Biology
- A student observes a wormlike organism crawling about on dead organic matter. Later, the organism sheds its outer covering. One possibility is that the organism is a larval insect (like a maggot). However, it might be a member of the phylum ________, and one way to distinguish between the two possibilities is by looking for ________.
- Nematode worms and annelid worms share which of the following features?
- How many of the following can be used to distinguish a nematode worm from an annelid worm? 1. type of body cavity 2. number of muscle layers in the body wall 3. presence of segmentation 4. number of embryonic tissue layers 5. shape of worm in cross-sectional view
- Humans most frequently acquire trichinosis by
- Which of the following is a characteristic of nematodes?
- Which of the following is found only among annelids?
- A radula is present in members of which clade(s)?
- A terrestrial mollusc without a shell belongs to which clade?
- Which mollusc clade includes members that undergo embryonic torsion?
- If a lung were to be found in a mollusc, where would it be located?
- A brachiopod can be distinguished from a bivalve by the presence of
- While sampling marine plankton in a lab, a student encounters large numbers of fertilized eggs. The student rears some of the eggs in the laboratory for further study and finds that the blastopore becomes the mouth. The embryo develops into a trochophore larva and eventually has a true coelom. These eggs probably belonged to a(n)
- The larvae of many common tapeworm species that infect humans are usually found
- What would be the most effective method of reducing the incidence of blood flukes in a human population?
- Planarians lack dedicated respiratory and circulatory systems because
- The excretory organs of annelids are
- Against which hard structure do the circular and longitudinal muscles of annelids work?
- The organ(s) of respiratory gas exchange in oligochaetes is (are)
- Which characteristic(s) is (are) shared by both cnidarians and flatworms?
- Corals are most closely related to which group?
- Which clade in the phylum Cnidaria includes "jellies" with rounded (as opposed to boxlike) medusae?
- The members of which clade in the phylum Cnidaria occur only as polyps?
- Which of the following is true of members of the phylum Cnidaria?
- How many of the following are characteristics of at least some members of the phylum Cnidaria? 1. a gastrovascular cavity 2. a polyp stage 3. a medusa stage 4. cnidocytes 5. a pseudocoelom
- Sponges are most accurately described as
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