Chapter 32 Questions

Question 1

As you are on the way to Tahiti for a vacation, your plane crash lands on a previously undiscovered island. You soon find that the island is teeming with unfamiliar organisms, and you, as a student of biology, decide to survey them (with the aid of the Insta-Lab Portable Laboratory you brought along in your suitcase). You select four organisms and observe them in detail, making the notations found in the figure.
Table.
Organism A: microscopic, unicellular, with a flagellum; swims around in freshwater pools; envelops and consumes other microscopic organisms; mates with others, young bud off
Organism B: shaped like a basketball, covered with purple filaments, multicellular; rolls slowly across grassy fields; thrives with access to only freshwater and sunlight; mates with others, young emerge from hardened spherical structures
Organism C: hard and branched, multicellular, covered in a sticky coating; attached to rocky surfaces; traps insects in sticky coating and dissolves them; no mating, releases winged young that fly off and affix to bare rocks
Organism D: multicellular with cell walls; flies across fields; constructs nets to trap flying organisms, and sucks out internal fluids; mates with others, and disperses young ballistically
Which organism would you classify as an animal?
a. organism A
b. organism B
c. organism C
d. organism D

Answer 1

c. organism C

Question 2

Trichoplax dhaerens is the only living species in the phylum Placozoa. Individuals are about 1 mm wide and only 27 micrometers 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. Individual animals move using cilia, and any “edge” can lead. T. adhaerens 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. T. adhaerens sperm cells have never been observed, nor have embryos past the 64-cell (blastula) stage.
Which of the following T. adhaerens traits is different from all other known animals?
a. T. adhaerens is multicellular.
b. T. adhaerens has cilia.
c. T. adhaerens lacks cell walls.
d. T. adhaerens lacks muscle and nerve cells.

Answer 2

d. T. adhaerens lacks muscle and nerve cells.

Question 3

Whatever its ultimate cause(s), the Cambrian explosion is a prime example of ___.

a. adaptive radiation
b. mass extinction
c. evolutionary stasis
d. a large meteor impact

Answer 3

a. adaptive radiation

Question 4

In individual insects of some species, whole chromosomes that carry larval genes are eliminated from the genomes of somatic cells at the time of metamorphosis. A consequence of this occurrence is that ___.

a. we could not clone a larva from the somatic cells of such an adult insect
b. the descendants of these adults do not include a larval stage
c. metamorphosis can no longer occur among the descendants of such adults
d. such species must reproduce only asexually

Answer 4

a. we could not clone a larva from the somatic cells of such an adult insect

Question 5

The evolution of animal species has been prolific (current estimates of species numbers reach into the tens of millions). Much of this diversity is a result of the evolution of novel ways to ___.

a. sense, feed, and move
b. reproduce
c. form an embryo and establish a basic body plan
d. arrange cells into tissues

Answer 5

a. sense, feed, and move

Question 6

Arthropods invaded land about 100 million years before vertebrates. This fact most clearly implies that ___.

a. arthropods evolved before vertebrates did
b. extant terrestrial arthropods are better adapted to terrestrial life than are extant terrestrial vertebrates
c. arthropods have had more time to coevolve with land plants than have vertebrates
d. vertebrates evolved from arthropods

Answer 6

c. arthropods have had more time to coevolve with land plants than have vertebrates

Question 7

While looking at some seawater through your microscope, you spot the egg of an unknown animal. Which of the following tests could you use to determine whether the developing organism is a protostome or a deuterostome? See whether the embryo ___.

a. develops a blastopore
b. develops an archenteron
c. develops germ layers
d. exhibits spiral cleavage or radial cleavage

Answer 7

d. exhibits spiral cleavage or radial cleavage

Question 8

Which of the following is a feature of the “tube-within-a-tube” body plan in most animal phyla?

a. The outer tube consists of a hard exoskeleton.
b. The mouth and anus form the ends of the inner tube.
c. The outer tube consists of digestive organs.
d. The two “tubes” are separated by tissue that comes from embryonic endoderm.

Answer 8

b. The mouth and anus form the ends of the inner tube.

Question 9

A student encounters an animal embryo at the eight-cell stage. The four smaller cells that comprise 1 hemisphere of the embryo seem to be rotated 45 degrees and to lie in the grooves between larger, underlying cells. This embryo may potentially develop into a(n) ___.

a. earthworm
b. sea urchin
c. turtle
d. sea star

Answer 9

a. earthworm

Question 10

What was an early selective advantage of a coelom in animals? A coelom ___.

a. allowed asexual and sexual reproduction
b. allowed cephalization and the formation of a cerebral ganglion
c. contributed to a hydrostatic skeleton, allowing greater range of motion
d. was a more efficient digestive system

Answer 10

c. contributed to a hydrostatic skeleton, allowing greater range of motion

Question 11

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

a. Cnidarians have fewer Hox genes than bilaterians.
b. The presence of collar cells.
c. All cnidarians are acoelomate.
d. Cnidarian larvae possess anterior-posterior, left-right, and dorsal-ventral aspects.

Answer 11

d. Cnidarian larvae possess anterior-posterior, left-right, and dorsal-ventral aspects.

Question 12

An organism that exhibits a head with sensory equipment and a brain probably also ___.

a. is segmented
b. is diploblastic
c. has a coelom
d. is bilaterally symmetrical

Answer 12

d. is bilaterally symmetrical

Question 13

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 would be a likely mechanism by which this pesticide works?

a. The mosquito would have trouble digesting food, due to impaired gut function.
b. The mosquito would develop a weakened exoskeleton that would make it vulnerable to trauma.
c. The mosquito would have trouble with respiration and circulation, due to impaired muscle function.
d. The mosquito wouldn’t be affected at all.

Answer 13

a. The mosquito would have trouble digesting food, due to impaired gut function.

Question 14

Which of the following statements comparing symmetry in sessile and swimming animals is most probable?

a. Radial symmetry occurs most frequently in animals that catch their prey by rapid swimming.
b. Radial symmetry is more advantageous for active swimming than is bilateral symmetry.
c. Bilateral symmetry allowed animals to evolve nerves.
d. Bilaterally symmetric animals can be streamlined for swimming, but radially symmetric animals cannot.

Answer 14

d. Bilaterally symmetric animals can be streamlined for swimming, but radially symmetric animals cannot.

Question 15

What should animals with radial symmetry be better able to do than those with bilateral symmetry?

a. move quickly in one direction
b. detect threats from above or below equally well
c. deal effectively with food distributed homogeneously in all directions
d. focus attention in a single direction

Answer 15

c. deal effectively with food distributed homogeneously in all directions

Question 16

Scientists researching the origins of multicellularity compared domains of _____ proteins of unicellular organisms with those of certain animals.

a. fibrillin
b. collagen
c. elastin
d. cadherin
e. keratin

Answer 16

d. cadherin

Question 17

Which of the following triploblastic organisms is incorrectly paired with its body cavity classification?

a. flatworm—pseudocoelomate
b. earthworm—coelomate
c. planarian—acoelomate

Answer 17

a. flatworm—pseudocoelomate

Question 18

In which type of cleavage pattern does each cell have the capacity to develop into a complete embryo?

a. determinate cleavage
b. indeterminate cleavage
c. spiral cleavage
d. none of the above

Answer 18

b. indeterminate cleavage

Question 19

Which taxonomic level contains the other choices?

a. Deuterostomia
b. Lophotrochozoa
c. Ecdysozoa
d. Eumetazoa

Answer 19

d. Eumetazoa

Question 20

Which is not true of the Neoproterozoic era?

a. Soft-bodied, multicellular eukaryotes could be found.
b. Molluscs, sponges, and cnidarians could be found.
c. Predation existed.
d. Animal diversity decreased.
e. Glaciers killed most life on Earth.

Answer 20

d. Animal diversity decreased.

Question 21

Which characterize(s) an animal body plan?

a. symmetry
b. tissues
c. body cavity
d. a and c
e. a, b, and c

Answer 21

e. a, b, and c

Question 22

Place these groups in the order in which they appeared: 1. Porifera 2. Cnidaria 3. Aceola 4. Nematoda
Figure: Phylogenetic tree
a. 2, 3, 4, 1
b. 1, 2, 3, 4
c. 3, 4, 1, 2
d. 4, 3, 1, 2
e. 3, 2, 4, 1

Answer 22

b. 1, 2, 3, 4

Question 23

Which is a member of the Bilateria?
Figure: Phylogenetic tree
a. Porifera
b. Nematoda
c. Cnidaria
d. Ctenophora

Answer 23

b. Nematoda

Question 24

You are dissecting an unidentified animal. It is radially symmetric and has no body cavity. To what phylum might it belong?

a. Cnidaria
b. Chordata
c. Platyhelminthes
d. Annelida
e. Arthropoda

Answer 24

a. Cnidaria

Question 25

You are dissecting an unidentified animal. It is bilaterally symmetric and has no body cavity. To what phylum might it belong?

a. Cnidaria
b. Chordata
c. Platyhelminthes
d. Annelida
e. Arthropoda

Answer 25

c. Platyhelminthes

Question 26

One of the characteristics unique to animals is

a. gastrulation.
b. multicellularity.
c. sexual reproduction.
d. flagellated sperm.

Answer 26

a. gastrulation.

Question 27

The distinction between sponges and other animal phyla is based mainly on the absence versus the presence of

a. a body cavity.
b. a complete digestive tract.
c. mesoderm.
d. tissues.

Answer 27

d. tissues.

Question 28

Which of the following was probably the least important factor in bringing about the Cambrian explosion?

a. the emergence of predator-prey relationships
b. an increase in the concentration of atmospheric oxygen
c. the movement of animals onto land
d. the origin of Hox genes

Answer 28

c. the movement of animals onto land

Question 29

Based on the tree in Figure 32.11, which statement is false?

a. The animal kingdom is monophyletic.
b. Acoelomate flatworms are more closely related to echinoderms than to annelids.
c. Sponges are basal animals.
d. Bilaterians form a clade.

Answer 29

b. Acoelomate flatworms are more closely related to echinoderms than to annelids.