2 Protozoa
n 2.1 THE CLASSIFICATION OF PARASITIC PROTOZOA
The protozoa are large collection of organisms that have only one thing in common in
that they are all unicellular. They are all grouped together into a subkingdom which is
divided into several phyla.
n BOX 2.1 THE MAIN CHARACTERISTICS OF THE PROTOZOA
nSingle celled or unicellular.
nEntire body bounded by a plasmalemma.
nThe cytoplasm is bounded by a clear outer gelatinous region the ectoplasmand an inner
more fluid region the endoplasm.
nWithin the cytoplasm are the organelles; nucleus (or in some species nuclei), nucleolus,
chromosomes, Golgi bodies, endoplasmic reticulum, lysosomes, centrioles, mitochondria
and in some cases chloroplasts.
nOrganelles unique to protozoa: contractile vacuoles, trichocysts and toxicysts.
nContractile vacuoles are organelles involved in expelling water from cytoplasm, for vol-
ume regulation and osmotic regulation.
nTrichocysts develop within membrane-bound vesicles in the cytoplasm and end up in the
periphery of the cytoplasm. Form into elongated capsules triggered by mechanical and/or
chemical stimuli — discharge a long, thin filament.
nToxicysts are related structures involved in predation — discharged filaments paralyse
prey and initiate digestion.
nReproduction
nAsexual reproduction occurs in all groups and sexual reproduction in most groups.
nAsexual reproduction does not by definition generate new genotypes.
nFission, a controlled mitotic replication of chromosomes and splitting of the parent into
two or more parts.
nBinary fission, splitting of the individual into two.
