ANIMAL DIVERSITY EXAM ANSWER:
1.
Protists typically reproduce asexually. However, some protists undergo sexual reproduction during times of
environmental stress. What advantage does sexual reproduction give a protist during these times?
Sexual reproduction provides greater genetic variability in the next generation. New gene combinations that are
adaptive under the specific environmental stress may enhance the survival and reproduction of offspring with the
favorable genotype.
2.
What characteristics allowed vertebrates to attain great sizes?
Several of the characteristics that make a vertebrate a vertebrate also contributed to its increased size. By forming a
vertebral column and endoskeleton, the vertebrate was able to grow larger because internal bones could support
additional weight and allowed for improved locomotion of a larger animal. The formation of internal organs allowed
compartmentalization of bodily functions (i.e., digestion, respiration, circulation, etc.), which increased efficiency in a
larger animal. The localization of neural functions in a "head" centralized the nervous system and allowed it to
function more efficiently in a larger animal.
3.
What limits the ability of amphibians to occupy the full range of terrestrial habitats and allows other terrestrial
vertebrates to occupy them successfully?
Amphibians are limited from expanding into all terrestrial habitats by their reliance on water, both to keep their
bodies moist for cutaneous respiration and to use for reproduction. If water isn't readily available in a habitat,
amphibians will not be able to survive. Reptiles and mammals are able to dominate in habitats where amphibians
would die due to dehydration but even reptiles are limited to habitats that have moderate temperatures. Reptiles
cannot live in habitats that are too cold and need to modify their behavior to survive in extremely hot climates (such
as hiding during the day and only coming out at night when it's cooler).
4.
List some of the advantages that the early birds, in which flight was not nearly as efficient as it is in most of their
modern descendants, might have had as a result of the presence of feathers.
Feathers would have provided an advantage in insulation. Whether the early birds were endothermic or ectothermic,
the ability to trap in heat would have been an advantage in cooler climates. Feathers could have also provided a
protection from injury or infection. The feathers could have provided a cushion or layer that predator's teeth or
claws would have to penetrate or barrier that pathogens would have to penetrate in order to infect the animal.
5.
Scientists believe the ancestral mollusk had a very limited shell, consisting mainly of calcareous plates. The shell
became more developed in some groups but was lost in others. What is the evolutionary advantage of having a
shell? Of not having one?
A mollusk's shell provides the animal with protection. A snail can pull into its shell and a clam can close its
shell when threatened. However, a shell also limits mobility. Mollusks such as the cephalopods have
essentially lost their shells over time. The cephalopods are predatory animals and as such, mobility is
extremely important. The mobility that comes without a shell allows them to catch prey and escape attack if
threatened.
6.
Although arthropods are very successful in aquatic environments, what are the key adaptations that facilitated
the invasion of the land by arthropods?
The arthropods successfully invaded land with the adaptations of an exoskeleton, jointed appendages, a
respiratory system, and specialized structures such as compound eyes and wings. The exoskeleton increased
mobility over the hydrostatic skeleton of the worms because it allowed a more solid structure for the
anchoring of muscles. This allowed for the movement of individual appendages that increased speed and
agility. The jointed appendages also increase agility. The respiratory system in insects (spiracles and tubules)
and arachnids (book lungs) increased gas exchange in animals that were encased in a gas-impermeable
exoskeleton and reduced water loss. The adaptation of specialized structures such as compound eyes and
wings allowed terrestrial arthropods to better perceive and respond to changes in their environment.
7.
Why is it believed that echinoderms and chordates, which are so dissimilar, are members of the same
evolutionary line?
Two key evolutionary adaptations link these two animal lines together: deuterostome embryological
development and an endoskeleton. No other animal group has these two features. In fact, a main reason why
the echinoderms seem so different from the chordates is the radial symmetry that is present in the
echinoderms. The larval stage of the echinoderms is bilaterally symmetrical and it is believed that the radial
symmetry is a secondary adaptation to an aquatic environment.
8.
at type of organism spends most of its life cycle in the medusa body form? What type of organism spends most of its
life cycle in the polyp body form?
The jellyfish, class Scyphozoa, spend the majority of their lives in the medusa stage. During their life cycle they do
form polyps but this is a very short portion of their life cycle. The polyp forms the medusa, which buds off of the
polyp to become a free-floating organism. The sea anemones and corals, class Anthozoa, spend most of their life
cycles in the polyp stage. Another organism, the genus Hydra, spends its life cycle in the polyp stage. This is unique
among the organisms in its class Hydrozoa, which usually alternate between a polyp and medusa stage.
9.
Coral reefs are often found in nutrient-poor waters. What type of symbiotic relationship helps these coral animals grow
actively? What are the advantages for each member in the relationship? What would happen to the coral reefs if the
water they are growing in became cloudy with pollution?
Coral form symbiotic relationships with algae. Algae live among the coral animals producing nutrients through
photosynthesis that the coral feed on. The advantage for the coral is the nutrients produced by the algae. Although
coral are carnivorous, they obtain important nutrients from the algae. The advantage for the algae is the protection
provided by the coral. The coral provide a solid substrate on which the algae can settle and have access to light. If the
waters became polluted and cloudy, such that light was blocked from penetrating to the coral, the algae would soon
die. Without the algae, the coral would also die.
10. Parasites, especially those that require two or more hosts to complete their life cycles, often produce very large
numbers of offspring. What advantage would this present to them?
Parasites, like many organisms that have very little parental investment in rearing offspring, tend to produce a very
large number of offspring. The chances than any one offspring will survive to infect its host are very slim. The risks
are even greater when more than one host needs to be infected to complete its life cycle. The organism is merely
improving its chances of successful reproduction by producing a very large number of offspring.
11. In what ways is an earthworm more complex than a flatworm?
An earthworm, in the Annelida phylum, is a coelomate and a flatworm; in the Platyhelminthes phylum, is an
acoelomate. The presence of a body cavity in the earthworm allows for specialization of the internal organs,
compared to the flatworm. The coelom also leads to the evolution of a circulatory system in the earthworm that is
not present in the flatworm. The reproductive organs and gametes in the earthworm are also larger and more
diverse, which expands the reproductive strategies used by earthworms compared to flatworms.
12. Why is it believed that echinoderms and chordates, which are so dissimilar, are members of the same evolutionary line?
Chordates and echinoderms shared a very key characterization of animal taxonomy—that of embryo growth pattern.
These two groups comprise the deuterostomes whose embryological development differs greatly from the
protostomes (mollusks, annelids, and arthropods). These embryological developmental patterns are guided by
genetic differences in the expression of Hox genes, which suggests that echinoderms and chordates share a key
characteristic very distinct from other animal groups. And, although the adult echinoderms look very different from
the chordates, an earlier stage in their development looks more closely related to the chordates.
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