Page 285 - Biology_F5

Biology for Advanced Level Secondary Schools

feed on the cellulose, they convert it into Parasitism
simple compounds, which can be digested, Parasitism is a close association between
absorbed and assimilated by the ruminants. two organisms of different species,
Mutualistic form of symbiotic nutrition is whereby one organism called a parasite
also evident between leguminous plants benefits by obtaining its nutrients and
and nitrogen fixing bacteria, where by the shelter from another living organism
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bacteria accommodated within the root called a host. Normally, the parasite may
nodules of these plants fix nitrogen from ultimately cause harm to the host but, in
the air by converting it into nitrogen useful
nitrogenous compounds such as nitrates. some cases, it can exist without killing the
On one hand, these nutrients are required host. Some parasites, such as tapeworms
by plants for their growth and development. and liver flukes live in the internal organs
On the other hand, the bacteria benefit by or tissues of the host body. These types
getting shelter and synthesised nutrients of parasites are called endoparasites. On
from the plants. Algae and fungi form a the other hand, some parasites, such as
mutualistic association called lichen. In ticks and bed bugs attach themselves on
this relationship algae synthesise food the surface of the body of their living host
and supply some to the fungi while and suck fluids from them; and these are
the fungi cover the algae and protect it called ectoparasites. Both endoparasites
from desiccation. Also, fungi and roots and ectoparasites are highly adapted to
of vascular plants form a mutualistic their mode of nutrition. For example,
association called mycorrhizae. The role of most parasites have hooks and haustoria
fungi in this relationship is to increase the for attachment and for sucking nutrients
surface area for the plant roots absorption
of nutrients. The plant supplies some of from the host.
the manufactured food to the fungi which
normally cannot photosynthesise its food. (c) Holozoic nutrition
Holozoic nutrition is a form of
heterotrophic nutrition exhibited mainly
Commensalism by free living animals, which have a
Commensalism is a close association specialised digestive tract, also called
between two living organisms of different alimentary canal. The nutrition of this
species in which one organism benefits form involves several steps, such as
and the other organism neither benefits taking in solid or liquid food, followed
nor is harmed. For example, cattle egrets by mechanical and chemical digestion in
follow herds of cattle or buffalo and feed the alimentary canal. The digested food
on insects disturbed by the animals. The materials are reduced into simple forms,
cattle and buffalo are not harmed by which can be absorbed and assimilated by
the feeding activities of the cattle egret. the body cells. Holozoic organisms include

Therefore, in this association one member animals, such as herbivores which feed on
(the cattle egret) benefits while the other plants, carnivores, which feed on living
(cattle and buffalo) neither benefits nor is animals; omnivores, which feed on both
harmed. plants and flesh, and decomposers, which
feed on remains of dead animals and plants

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