LESSON 1
PHYLUM PROTOZOO: RHIZOPODA AND ZOOMASTIGOPHORA
Section I. OVERVIEW OF PROTOZOO
1-1.
GENERAL COMMENTS
Protozoans are unicellular (one-celled) organisms which belong to the
subkingdom Eucaryota. They vary in size from almost submicroscopic to 120
micrometers (mcm) in diameter. Each protozoan is a complete organism capable of
carrying out the same physiological functions performed by many cells in a more
complex organism. There are specialized and complex organelles found in protozoans
which perform the functions of locomotion, metabolism, and reproduction. It has been
suggested that instead of unicellular, the protozoan organisms should be termed
acellular because of the intricacy of their functions and also because some of these
organisms have more than one nuclei. The members of this phylum which are parasitic
to humans, while preserving the general characteristics of their free living counterparts,
are capable of survival in the adverse system of the host.
1-2.
HISTORY
Some protozoans are beneficial to mankind by being part of the food chain and
by serving as experimental subjects. Others have adapted well to a parasitic existence
causing many diseases in humans. Much has been discovered about protozoans since
Anton van Leeuwenhoek first saw the cysts of Giardia lamblia from his own stool and
reported them to the Royal Academy in his treatise "Wee besties." His discoveries
occurred in the late 1600's.
1-3.
STRUCTURE
The various forms and functions of protozoan cells are truly amazing for what we
consider as simple single-celled organisms. Whether they are amoeba, flagellates, or
ciliates, they contain ultramicroscopic organelles that enable them to perform many of
the activities observed in higher animals. However, the most easily recognized and
identifiable structure within the protozoan cell is the nucleus. Nuclei among the
protozoa usually are of two types, the vesicular nucleus with a clearly defined internal
space, and the compact nucleus which appears to be a solid mass. Most of the
protozoa which parasitize humans exhibit the vesicular type. Because nuclear
chromatin components can be stained and easily observed within the vesicular nucleus,
the arrangement of the chromatin, whether dispersed or condensed, is helpful in
differentiation of the species within certain classes of the Protozoo. See figures 1-1
and 1-2.
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1-2