Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 32
Test Yourself Questions
1. Which of the following is not a distinguishing characteristic of animals?
a. capacity to move at some point in life cycle
b. possession of cell walls
c. multicellularity
d. heterotrophic
e. all of the above are characteristics of animals
Answer: b. Animal cells do not have cell walls.
2. Terrestrial adaptations seen in animals include
a. internal fertilization.
b. tough, protective shells around eggs.
c. a waxy cuticle covering exposed tissue.
d. a and b only.
e. all of the above.
Answer: d. Internal fertilization and tough protective shells around eggs are adaptations that allowed for
terrestrial colonization by animals.
3. Eumetazoa are animals that have
a. true tissues.
b. more than one tissue type.
c. only one tissue type.
d. radial symmetry.
e. spiral cleavage.
Answer: b. Eumetazoa are animals that have more than one type of tissue.
4. The localization of sensory structures at the anterior end of the body is
a. bilateral symmetry.
b. spiral cleavage.
c. cephalization.
d. radial symmetry.
e. gastrulation.
Answer: c. Cephalization is the localization of sensory structures at the anterior end of the body.
5. The germ layer that is present in triploblastic animals but is absent in diploblastic animals is
a. the ectoderm.
b. the mesoderm.
c. the endoderm.
d. the pseudocoelom.
e. the coelom.
Answer: b. Triploblastic animals have ectoderm, mesoderm and endoderm. Diploblastic animals have
only the ectoderm and the endoderm.
6. Pseudocoelomates
a. lack a fluid-filled cavity.
b. have a fluid-filled cavity that is completely lined with mesoderm.
c. have a fluid-filled cavity that is partially lined with mesoderm.
d. have a fluid-filled cavity that is not lined with mesoderm.
e. have an air-filled cavity that is partially lined with mesoderm.
Answer: c. Pseudocoelomates have a fluid-filled cavity that is partially lined with mesoderm.
7. Protostomes and deuterostomes can be classified based on
a. cleavage pattern.
b. destiny of the blastopore.
c. whether the fate of the embryonic cells is fixed early during development.
d. how the coelom is formed.
e. all of the above.
Answer: e. Protostomes and deuterostomes differ in cleavage pattern, destiny of the blastopore, how
early the fate of the embryonic cells becomes fixed, and how the coelom forms.
8. Naturally occurring identical twins are possible only in animals that
a. have spiral cleavage.
b. have determinate cleavage.
c. are protostomes.
d. have indeterminate cleavage.
e. a, b, and c.
Answer: d. Animals with indeterminate cleavage have the potential to produce identical twins when
individual embryonic cells separate during development.
9. Genes involved in the patterning the body axis, that is, in determining characteristics such as neck
length and appendage formation, are called
a. small subunit (SSU) rRNA genes.
b. Hox genes.
c. metameric genes.
d. determinate genes.
e. none of the above.
Answer: b. Hox genes are important for patterning the body axis.
10. A major difference between the molecular phylogeny of animals and traditional phylogeny of
animals is that
a. the presence or absence of the mesoderm is not important in molecular phylogeny.
b. molecular phylogeny suggests that all animals do not share a single common ancestor.
c. body symmetry, whether radial or bilateral, is not an important determinant in molecular
phylogeny.
d. molecular phylogeny does not include the echinoderms in the deuterostome clade.
e. molecular phylogeny suggests that the presence or absence of a coelom is not important for
classification.
Answer: e. Molecular phylogeny suggests that the presence or absence of a coelom is not important for
classification.
Conceptual Questions
1. The traditional classification is based on what four features of animal body plans?
Answer: (1) Absence or existence of different tissue types. (2) Type of body symmetry. (3) Presence or
absence of a true body cavity. (4) Patterns of embryonic development.
2. Distinguish between radial and bilateral symmetry.
Answer: Radially symmetric animals can be divided equally by a longitudinal plane passing through the
central axis. Bilaterally symmetric animals can be divided along a vertical plane at the midline to create
two halves; thus, a bilateral animal has a left side and a right side, which are mirror images.
3.
Define cleavage and gastrulation.
Answer: Cleavage is a succession of rapid cell divisions with no significant growth that produces a
hollow sphere of cells called a blastula. In gastrulation, an area in the blastula invaginates and folds
inward, creating in the process different embryonic cell layers called germ layers.
Experimental Questions
1. What was the purpose of the study conducted by Aguinaldo and colleagues?
Answer: The researchers sequenced the complete gene that encodes small subunit rRNA from a variety
of representative taxa of animals to determine their phylogenetic relationships, particularly the
relationships of arthropods to other animal taxa.
2. What was the major finding of this particular study?
Answer: The results indicated a monophyletic clade containing arthropods and nematodes plus several
other smaller phyla. This clade was called the Ecdysozoa. The results of this study indicated that
nematodes were more closely related to the arthropods than previously believed.
3. What impact does the new view of nematode and arthropod phylogeny have on other areas of
research?
Answer: The fruit fly, Drosophila melanogaster, and the nematode, Caenorhabditis elegans, have been
widely studied to understand early development. Under the traditional phylogeny, these two species
were not considered to be closely related, so similarities in development were assumed to have arisen
early in animal evolution. With the closer relationship indicated by this study, these similarities may have
evolved after the divergence of the Ecdysozoan clade. This puts into question the applicability of studies
of these organisms to the understanding of human biology.
Collaborative Questions
1. Discuss the different types of body cavities.
Answer: In most animals, the body cavity is completely lined with mesoderm and is called a true coelom;
animals with a true coelom are called coelomates. Animals in which the coelom is not completely lined
with tissue derived from mesoderm are called pseudocoelomates, and their body cavity is termed a
pseudocoelom. Rotifers and nematodes are examples of animals which are pseudocoelomates.
Animals that lack a body cavity completely are called acoelomates. Their body is filled with a tissue
called mesenchyme instead of fluid. The flatworm is an example of an acoelomate.
2. Discuss some of the characteristics of animal life.
Answer: Despite the diversity of the animal kingdom there are some characteristics which are common
to all species of animals.
Multicellularity  All animals are multicellular.
Heterotrophs  All animals are heterotrophs, which means they obtain their food by eating other
organisms.
No cell walls  Unlike plants, fungi, and bacteria, animal cells do not have cell walls and rely on the
extracellular matrix to provide extra strength and support for cells.
Movement  Most animals have a muscular system that when combined with a nervous system allows
them to move in their environment.
Sexual reproduction  Most animals reproduce sexually, with small mobile sperm uniting with a much
larger egg to form a fertilized egg or zygote.