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Biology for Advanced Level Secondary Schools

Structure of Entamoeba histolytica areas with low oxygen supply such as
Entamoeba histolytica has a regular in the large intestine.
body, which changes constantly. The (e) They have rapid binary fission and
body is covered by a thin semi-permeable production of a large number of cysts
membrane called plasmallema or plasma to ensure their existence and perpetuation
membrane; and it is differentiated into in alternative hosts.
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two distinct portions; an outer ectoplasm
(plasmagel) and an inner endoplasm (f) They can feed on various foods, ranging
(plasmasol). In the endoplasm, there is from bacteria to blood cells, and digest
a prominent nucleus which is enclosed them using enzymes.
by a nuclear membrane. They possess
pseudopodia for locomotion and feeding
by engulfing food substances (Figure Exercise 3.3
3.12).
1. Give reasons as to why some
Ectoplasm Food vacuole taxonomists consider Protoctista
Endoplasm as an obsolete kingdom.
Nucleus
Pseudopodia 2. Explain the reason why both
Monera and Protoctists are single-
Plasmalema Ingested red celled organisms but belong to
blood cells
different kingdoms.
Figure 3.12: Structure of Entamoeba histolytica 3. Describe any five features which

Adaptations of Entamoeba to its mode make Amoeba a specialised form
of life of protoctists.

Some amoeba such as Naegleria are free 4. What is the economic importance
living; they can live in different habitats of Entamoeba?
such as on the bottom of ponds and lakes,
whereas others like Entamoeba exhibit a Phylum Zoomastigina
parasitic mode of life. Parasitic amoeba This phylum consists of flagellated
are adapted to their mode of life as follow: parasitic protoctists. It contains free-
(a) They can form cysts, which resist living organisms, some are symbionts,
digestive agents in the stomach. such as protozoans which live in the gut
(b) They lack contractile vacuoles, since of termites and digest cellulose in the
they live in isotonic state with the wood eaten by the termites, and some
host’s gut fluid. are parasites. Examples of parasitic
(c) They live where there is a plenty of food organisms found in this phylum include
supply from their host. Trypanosoma gambiense, a parasite

(d) They are physiologically tolerant to low causing African sleeping sickness.
oxygen concentration, since they live in

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