Page 125 - Biology_F5

Biology for Advanced Level Secondary Schools

Adaptations of Trypanosoma spp. to 3. Account for assertion that areas
their mode of life infested by tsetse flies are not
suitable for human settlement.
Trypanosoma spp. are highly adapted to
parasitic mode of life in their hosts due Phylum Apicomplexa
to possession of the following adaptive This phylum consists of eukaryotic
features: unicellular organisms, which are spore
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(a) They have large surface areas to forming parasites of animals. They are
volume ratio. This is important for also known as sporozoans; an example is
absorption of oxygen and food from the parasite Plasmodium, which causes
their hosts. malaria in humans.
(b) They live isotonically within the General characteristics of phylum
blood plasma of their hosts. They Apicomplexa
lack contractile vacuoles and (a) Most of them possess a unique type of
osmoregulation does not take place. plastid called an apicoplast, used for
(c) They have rapid reproductive rate and piercing host cells.
they reproduce by binary fission, which (b) They are unicellular and spore forming
ensures that large number of parasites
are produced. Large number of these organisms. Almost all species are
parasites is potentially important obligate endoparasites of animals, except
especially in adverse conditions, nephromyces, which live symbiotically
where many of the produced parasites with marine animals.
die. (c) They have an infectious stage known
(d) They have a hard pellicle that protects as sporozoite.
cytoplasmic structures and restricts (d) They reproduce asexually by schizogony
action of digestive enzymes of the and sexually by sporogony.
host.
(e) They are able to remain dormant in (e) The parasite changes its shape depending
on the host it inhabits.
their host’s cells of liver and spleen
during adverse conditions. This (f) They are non-motile.
ensures existence of the species. (g) They form resistant spores after
fertilisation.

Exercise 3.4
Distinctive features of phylum
1. Explain the distinctive features of Apicomplexa
the phylum Zoomastigina. Organisms in the phylum Apicomplexa differ

2. Your friend has been diagnosed from other groups by the following features:
with trypanosomiasis and is
curious about the organism that (a) They have a plastid called apicoplast,
causes the disease. Describe which is used for piercing the host cells.
the structure of the causative (b) They reproduce asexually by
organisms of the diagnosed schizogony in the human body and
disease. sexually by sporogony in the mosquito.

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