Page 79 - General and Inorganic Chemistry for Advanced Secondary Schools Students Book Form Five and Six

Biology for Secondary Schools

flowing streams containing decaying organic matter. A generalised structure of
amoeba is shown in Figure 5.7.

Cell membrane Food vacuole
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Nucleus
Pseudopodium
Endoplasm
Contractile vacuole
Cytoplasm
Ectoplasm

Figure 5.7: Generalised structure of amoeba

Characteristics of amoeba

(a) Amoeba have two layers of cytoplasm; a viscous outer layer called ectoplasm
and a more fluid internal layer called endoplasm.
(b) Most of them are free living, feeding on plant and animal matter. Others are
parasitic in animals, including human beings.
(c) They have pseudopodia which are used for both locomotion and feeding, as
shown in Figure 5.8.

Food vacuole

Pseudopodium
Food particle

Pseudopodia
(a) (b)

Figure 5.8: Amoeba using pseudopodia to (a) move (b)feed

(d) They have contractile vacuoles which regulate the amount of water in the
freshwater amoeba.

(e) They form temporary food vacuoles to hold and digest food particles.
(f) In amoeba, waste products, such as urea and ammonia are excreted by
simple diffusion. Diffusion is the movement of substances from a region

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