1). The traditional animal family tree places more significance on body plan (the presence of a coelom) while the rRNA tree places more significance on
a). embryological development patterns.
b). whether or not the animal molts.
d). all of these.
2). A key evolutionary development seen for the first time in the sponges is
a). a complete digestive system.
c). body symmetry.
3). All of the following are found in sponges except
c). a digestive tract.
d). sexual and/or asexual reproduction.
4). The first animal group to show extracellular digestion was the
5). Cnidarians project a nematocyst to capture their prey by
a). building up a high internal osmotic pressure.
b). ejecting it with a jet of water.
c). using a springlike apparatus.
d). muscle contractions that "throw" the nematocyst.
6). Which of the following is an example of an organism with the medusa body form?
a). a hydra
b). a coral
c). an anemone
d). a jellyfish
7). Key evolutionary advances of the flatworms are bilateral symmetry and
a). a coelom.
b). internal organs.
c). a one-way digestive tract.
d). a body cavity.
8). For excretion, flatworms use
c). flame cells.
9). The type of body cavity seen in the roundworms is called a(n)
d). gastrovascular cavity.
10). The type of pseudocoelomates found in soil, freshwater and marine environments, and as parasites are
Test Your Visual Understanding
1). What phylum is represented by the two organisms pictured in this figure, and what are some general characteristics of this phylum?
Answer: The phylum Cnidaria, more commonly referred to as the cnidarians, contains animals that have two basic body forms during their life cycles, the polyp stage and the medusa stage. Cnidarians are mostly marine organisms. They have radial symmetry and distinct tissues (epidermis, mesoglea, and gastrodermis). Some organisms alternate between a polyp and medusa stage in their life cycles while some spend most or all of their lives in one stage or the other. They are carnivores, capturing their prey with specialized "weapons" called nematocysts that are held within special cells called cnidocytes. They reproduce both sexually and asexually. A major evolutionary advance seen in the cnidarians, in addition to the presence of distinct tissues, is the internal extracellular digestion of food.
2). What 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?
Answer: 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.
Apply Your Knowledge
1). A sponge is a filter feeder, which means it eats by filtering food from the water that passes through its pores and out its osculum. Assume a sponge filters 1.8 milliliters of water per second. How much water is filtered in an hour? In a day?
Answer: If a sponges filters 1.8 ml of water/second and there are 60 seconds in a minute and 60 minutes in an hour, it will filter 6,480 ml of water in 3600 seconds or one hour. If it filters 6480 ml of water in one hour then it will filter 155,520 ml of water in 24 hours or in one day.
2). 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?
Answer: 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.
3). 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?
Answer: 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.