Page 104 - General and Inorganic Chemistry for Advanced Secondary Schools Students Book Form Five and Six

Biology for Secondary Schools

Questions takes place by simple diffusion.
1. How does the body structure of (i) Their bodies are bilaterally
a tapeworm differ from that of a symmetrical. This means their
liver fluke? bodies can be divided longitudinally
2. What is the function of suckers into two equal parts.
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in platyhelminths? (j) They are hermaphrodites, meaning
that they have both male and

General characteristics of female reproductive organs. Hence,
platyhelminths their reproduction can either be
(a) They have dorso-ventrally flattened through self-fertilisation or cross-
bodies. This is the reason why they fertilisation.
are called flatworms. (k) They are heterotrophic, meaning
(b) Most flatworms have only that they get food from other
one opening that is the mouth. organisms. Flatworms may be
However, tapeworms lack both parasites, predators or scavengers.
mouth and anus.
(c) They have no body cavity. A body Hook Rostellum
cavity is a space in an organism
which holds and protects internal Scolex
organs. Mature
(d) Some members have hooks and Sucker proglottid
suckers for attachment to the host. Neck
Such members include tapeworms
and the liver fluke. See Figure 5.27. Immature
(e) Some flatworms, such as planaria proglottid
have hair-like structure called cilia Figure 5.27: External structure of
on their outer body surface for tapeworm
locomotion.
(f) Few members, such as planaria are Distinctive features of platyhelminths
free living and inhabit freshwater, (a) They are dorso-ventrally flattened
marine water and land. Most of its with ribbon or leaf-like body.
members, such as liver flukes and
tapeworms are parasitic. (b) If present, their digestive system
(g) They have specialised cells for is incomplete. The digestive tract
excretion and osmoregulation has only a single opening which is
called flame cells. the mouth.
(h) They lack respiratory and circulatory (c) They have specialised cells for
systems. Transportation of oxygen excretion and osmoregulation
for respiration and other materials called flame cells.

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