Question 1

Which of the following characteristics represents the oldest branch point in animal phylogeny?

Accepted Answer

The oldest branch point in animal phylogeny is the distinction between animals with true tissues (Eumetazoa) and those without true tissues (such as sponges, Phylum Porifera). This fundamental difference represents the earliest divergence in the animal kingdom.

Question 2

A student encounters an animal embryo at the eight-cell stage. The four smaller cells that comprise one hemisphere of the embryo seem to be rotated 45° and to lie in the grooves between larger, underlying cells. If we were to separate these eight cells and attempt to culture them individually, then what is most likely to happen?

Accepted Answer

The description of the embryo suggests spiral cleavage, typical of protostomes. In such organisms, the fate of the cells is determined early, and separated cells are unlikely to develop into complete embryos.

Question 3

Among organisms exhibiting protostome development, which morphological trait shows the most variation?

Accepted Answer

Protostomes can have different types of body cavities (acoelomate, pseudocoelomate, and coelomate), which shows significant variation among different groups, unlike the other traits listed which are more conserved within protostomes.

Question 4

Which of the following was an early selective advantage of a coelom in animals?

Accepted Answer

The coelom acts as a fluid-filled cavity that can change shape but not volume, providing a hydrostatic skeleton that supports the body and allows for a greater range of motion. This was a significant evolutionary advantage for early coelomates, enabling more complex movements and body structures.

Question 5

Which of the following statements is correct regarding animal body plans?

Accepted Answer

The body plans observed in animals today have been shaped by natural selection, meaning those plans have provided evolutionary advantages in their respective environments over time.

Question 6

While observing seawater through a microscope, you spot the embryo of an unknown animal. Which of the following criteria could you use to determine whether the organism exhibits protostome or deuterostome development?

Accepted Answer

Spiral cleavage is characteristic of protostomes, while radial cleavage is characteristic of deuterostomes. This distinction in the pattern of cell division during early embryonic development is a key criterion for differentiating between the two groups.

Question 7

Which of the following characteristics in an organism would indicate that lacks a coelom?

Accepted Answer

Organisms lacking a coelom (acoelomates) do not have a fluid-filled body cavity between the digestive tract and the body wall. Therefore, muscular activity of the digestive system can distort the body wall, as there is no coelomic cavity to absorb and distribute the forces generated by such activity.

Question 8

In the earthworm body plan, the digestive system can be described as a "tube-within-a-tube." Where would you expect to find most of the tissues that developed from endoderm?

Accepted Answer

The endoderm is the innermost germ layer that develops into the lining of the digestive tract and other internal organs. In the "tube-within-a-tube" body plan, the digestive tract is the "straw," so the endoderm would line the inside of this "straw."

Question 9

Which of the following is a feature of the digestive tube in most animal phyla?

Accepted Answer

The digestive tube in most animal phyla features a mouth at one end and an anus at the other, forming the ends of the inner tube through which food enters and exits the body. This arrangement allows for a more efficient digestion process compared to a single opening serving both as mouth and anus.

Question 10

Suppose a researcher for a pest-control company developed a chemical that inhibited the development of an embryonic mosquito's endodermal cells. Which of the following best explains the effectiveness of the pesticide?

Accepted Answer

The endoderm is the innermost layer of an embryo, which develops into the lining of the digestive and respiratory systems. If a chemical inhibits the development of endodermal cells in mosquitoes, it would impair the development of these systems, particularly the gut, leading to difficulties in digesting food.

Question 11

Trichoplax adhaerens is the only living species in the phylum Placozoa. Individuals are about 1 mm wide and only 27 μm high, and are irregularly shaped. There are four types of cells, none of which are nerve or muscle cells, and none of which have cell walls. Individual animals move using cilia, and feed on marine microbes.
The body symmetry of T. adhaerens is likely to be most similar to which of the following groups of organisms?

Accepted Answer

Most sponges exhibit asymmetry or a very simple level of organization without a defined symmetry, similar to Trichoplax adhaerens, which also lacks complex structures and symmetry found in more evolved organisms.

Question 12

Which of these statements, if accurate, would support the claim that the ancestral cnidarians had bilateral symmetry?

Accepted Answer

Cnidarian larvae possessing anterior-posterior, left-right, and dorsal-ventral aspects would indicate a form of bilateral symmetry at some stage of their life cycle, supporting the claim that ancestral cnidarians had bilateral symmetry.

Question 13

In examining an unknown animal species during its embryonic development, how can you be sure what you are looking at exhibits protostome or deuterostome development?

Accepted Answer

The key difference between protostomes and deuterostomes is how their coelom (body cavity) develops. In deuterostomes, the coelom develops from the archenteron (the primitive gut), which is a characteristic not seen in protostomes. This feature is a definitive way to distinguish between the two types of development during the embryonic stage.

Question 14

Use the information to answer the question.
One small animal phylum (Placozoa) contains only two species, Trichoplax adhaerens (T. adhaerens) and T. reptans. There are four types of cells, none of which are nerve or muscle cells, and none of which have cell walls. T. adhaerens sperm cells have never been observed. Embryos up to, but not past, the 64-cell (blastula) stage have been observed.
On the basis of information in the paragraph, which of these should be able to be observed in T. adhaerens?

Accepted Answer

Since T. adhaerens embryos up to the 64-cell stage have been observed, it implies that fertilization occurs, which necessitates the presence of eggs, even though sperm cells have not been observed.

Question 15

Soon after the coelom begins to form, a researcher injects a dye into the coelom of a deuterostome embryo. Into which of the following structures would you expect the dye to flow?

Accepted Answer

In deuterostomes, the coelom typically forms from pockets that pinch off from the archenteron, which is the embryonic precursor to the gut. Therefore, injecting dye into the coelom of a deuterostome embryo would most likely result in the dye flowing into the archenteron.

Question 16

If an organism exhibits a head with sensory structures, which of the following characteristics would it likely also exhibit?

Accepted Answer

Organisms with a head and sensory structures typically exhibit bilateral symmetry, as this body plan supports directional movement and the concentration of sensory organs in the head region for environmental interaction.

Question 17

What do many organisms with deuterostome development have in common?

Accepted Answer

Deuterostomes are characterized by the blastopore, the first opening that forms during early embryonic development, becoming the anus. This is a key feature distinguishing them from protostomes, where the blastopore becomes the mouth.

Question 18

The protostome developmental sequence arose just once in evolutionary history, resulting in two main subgroups-Lophotrochozoa and Ecdysozoa. What does this finding suggest?

Accepted Answer

The finding suggests that the division into Lophotrochozoa and Ecdysozoa occurred after the establishment of the protostome developmental sequence, indicating they share a common ancestor that already exhibited this form of development.

Question 19

A student encounters an animal embryo at the eight-cell stage. The four smaller cells that comprise one hemisphere of the embryo seem to be rotated 45° and to lie in the grooves between larger, underlying cells. Which of the following organisms is this embryo most likely to develop into?

Accepted Answer

The answer of A student encounters an animal embryo at...

Question 20

Body symmetry in animals affects swimming in which of the following ways?

Accepted Answer

Bilaterally symmetric animals can be streamlined, which is advantageous for swimming, whereas radially symmetric animals, typically not moving actively or quickly, do not benefit from streamlining in the same way.

Quiz 32: An Introduction to Animal Diversity