Page 124 - Biology_F5

Comparative studies of natural groups of organisms

General characteristics of phylum Structure of Trypanosoma
Zoomastigina The genus Trypanosoma contains a
(a) The phylum Zoomastigina contains large number of parasitic species, which
organisms such as Trichonympha and infect wild animals, domesticated
Trypanosoma, which have one or two animals and humans. Trypanosoma is
flagella. divided into several sub-genera based
FOR ONLINE READING ONLY
(b) The members of this phylum are on morphological differences. Different
heterotrophic; single-celled organisms. species of trypanosomes are transmitted

(c) The phylum consists of both free-living by insects such as tsetsefly. An example
and parasitic organisms. Free-living is Trypanosoma gambiense, which is a
Zoomastigina are found in ponds and causative agent of sleeping sickness in
puddles with plenty of organic matter, humans. This parasite is common in west
while a few such as Trypanosoma are and central Africa, its vector is a tsetse fly,
parasites. Glossina palpalis. It is about 15 µm long,
(d) Some have undulating membrane. and 1 µm wide, pointed at both ends and
(e) Most of them reproduce by simple bears a prominent ovoid nucleus in the
binary fission. central region. It is enclosed in a strong
(f) The body is overlaid by a semi-rigid pellicle, which maintains the body shape.
pellicle. The entire body is covered by a wavy
undulating membrane. Along the edge
Distinctive features of phylum of the membrane is a flagellum attached
Zoomastigina posteriorly to a small granule known as a
Members of phylum Zoomastigina differ blepharoplast (basal body). Anteriorly, the
from the other members of the kingdom flagellum projects in front of the body as a
Protoctista by being the only heterotrophic short, fine slash, and immediately posterior
unicellular eukaryotes with one or more to the basal body, there is a prominent
flagella. granule, a parabasal body (Figure. 3.13).

Free flagellum
Undulating membrane Kinetoplast

Parabasal body

Pellicle Cytoplasm

Nucleus

Figure 3.13: Structure of a Trypanosoma

Form Five Student’s Book
117