Sporozoans - Advanced
Douglas Wilkin, Ph.D.
Niamh Gray-Wilson
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Printed: December 21, 2015
AUTHORS
Douglas Wilkin, Ph.D.
Niamh Gray-Wilson
www.ck12.org
C HAPTER
Chapter 1. Sporozoans - Advanced
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Sporozoans - Advanced
• Understand the complicated life cycle of sporozoans.
• Discuss some characteristics unique to sporozoans.
Will being bit by a mosquito give you malaria?
No, unless the mosquito is carrying the Plasmodium parasite. Though this animal-like protist does not have cilia or
flagella, there are stages during its life cycle when it is motile: the sporozoite, trophozoite, and merozoite stages.
Phylum Apicomplexa: Sporozoans
The sporozoans are able to form spore-like cells, from which they get their name. Sporozoans do not have flagella,
cilia, or pseudopodia. They are capable of gliding movements. All sporozoans are parasites of animals and cause
disease. They are also characterized by the presence of a unique cellular structure called an apical complex. The
apical complex secretes enzymes which allow the sporozoan to enter a host cell.
Most sporozoans have a complex life-cycle, involving both asexual and sexual reproduction. Typically, a host is
infected by ingesting cysts, which divide to produce sporozoites that enter the host’s cells. Eventually, the cells
burst, releasing merozoites which infect new host cells. This may occur several times until gamonts are produced.
The gamonts then form gametes that fuse to create new cysts, and the cycle continues. Many sporozoans will have
more than one host. This lifecyle is similar in many sporozoans.
The Apicomplexa are a large group of sporozoan protists. The malaria causing protist Plasmodium is a member of
this group and will be discussed in the Animal-like Protists: Diseases (Advanced) concept. See An Introduction to
the Apicomplexa at http://dna.kdna.ucla.edu/parasite_course-old/intro_to_apicomplexa_files/new_page_2.htm for
additional information.
Vocabulary
• apical complex: A unique organelle found in sporozoans that secretes enzymes which allow the sporozoan to
enter a host cell.
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• gamonts: Protozoan gametocytes.
• merozoites: Sporozoan cells released from a host cell after protozoan asexual replication.
• sporozoans: A group of protists that are able to form spore-like cells.
• sporozoites: The sporozoan cell form that infects new hosts.
Summary
• Members of Apicomplexa are parasites with no specialized locomotive organelles. Some of them can form
spores.
• Most sporozoans have a complex life-cycle, involving both asexual and sexual reproduction.
Practice
Use this resource to answer the questions that follow.
• Sporozoa at http://www.encyclopedia.com/topic/Sporozoa.aspx
1. Describe the structure of the apical complex.
2. How is Toxoplasma gondii transmitted?
Review
Use this image of a unicellular organism to answer the following two questions:
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Chapter 1. Sporozoans - Advanced
1. Is this organism an ameboid, a flagellate, or a ciliate? Explain your answer.
2. In what type of environment would you most likely find this organism?
3. Briefly describe the sporozoan life cycle.
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