Name ______________________________ Class ___________________ Date __________________
CHAPTER 34 ACTIVE READING WORKSHEETS
Read the passage below, which covers topics from your textbook. Answer the questions that follow.
Flukes have complicated life cycles. A good example is provided by the trematode blood flukes of the genus Schistosoma . Adult schistosomes live inside human blood vessels. Therefore, a human is the schistosome’s primary host, the host from which the adult parasite gets its nourishment and in which sexual reproduction occurs. Unlike most flukes, schistosomes have separate sexes. Eggs produced by the female are fertilized by the male. Some of the fertilized eggs make their way to the host’s intestine or bladder and are excreted with the feces or urine. Those that enter fresh water develop into ciliated larvae that swim. If the larvae encounter a snail of a particular species within a few hours, they burrow into the snail’s tissues and begin to reproduce asexually. The snail serves as the schistosome’s intermediate host, the host from which the larvae derive their nourishment. Eventually, the larvae develop tails and escape from the snail. These tailed larvae swim through the water. If they find the bare skin of a human, they penetrate the skin, enter a blood vessel, and develop into adults. At that point, the cycle begins again.
Write your answers in the spaces provided.
SKILL: Sequencing Information
1. Order the statements to show the life cycle of schistosomes. Write “1” on the line in front of the statement that describes what happens first. Write “2” on the line in front of the statement that describes what happens next, and so on.
____ a.Tailed larvae leave the intermediate host.
____ b.The fertilized eggs are excreted with feces or urine.
____ c.The larvae enter a human blood vessel and develop into adults.
____ d.The larvae burrow into a snail’s tissues.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Modern Biology 141 Platyhelminthes

Name ______________________________ Class ___________________ Date __________________
___ e.The eggs are fertilized by a male.
____ f.The larvae penetrate the skin of a new primary host.
____ g.In a freshwater environment, the eggs develop into ciliated larvae.
____ h.Once inside an intermediate host, the larvae reproduce asexually.
____ i.An adult female schistosome releases eggs inside a primary host.
2. The figure illustrates the life cycle of an adult blood fluke. Insert the following labels on the diagram: “Ciliated larvae,” “Egg,” “Eggs,” “Intermediate host,”
“Primary host,” and “Tailed larva.”
Read the question and write your answer in the space provided.
SKILL: Vocabulary Development
3. What is the meaning of the term ciliated in the passage?
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Circle the letter of the word or phrase that best completes the analogy.
4. In the life cycle of a blood fluke, primary host is to human as secondary host is to a. fresh water. b. tailed larva. c. snail. d. blood vessel.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Modern Biology 142 Platyhelminthes