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Nutrition

Food materials synthesised by autotrophs (a) Saprophytic nutrition
are in the form of complex molecules, This type of nutrition is also referred
which contain chemical energy locked to as saprotrophic nutrition. The term
in their bonds. Heterotrophs ingest large saprotroph comes from two Greek words;
molecules and they require a digestive sapros and trophos where sapros means
system to break down large food ‘rotten’ and trophos means ‘feeder.’ This
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molecules into simpler forms which can type of nutrition involves organisms
be absorbed for utilisation in their bodies. feeding on soluble organic compounds
Furthermore, they require energy to obtained from dead or decaying bodies
carry out life processes, such as cellular of other organisms, mainly plants and
metabolism. animals. Digestion is accomplished
by producing extracellular digestive
Some bacteria form a special group of enzymes, which reduce the tissues of the
heterotrophs called photoheterotrophs. dead or decaying organisms into solution
These bacteria can utilise organic raw form, which can be readily taken up.
materials to synthesise their food in Most bacteria and fungi, such as Mucor,
the presence of light energy. Animals, Rhizopus, and yeast are saprotrophs.
including human beings utilise six
different types of nutrients for proper (b) Symbiotic nutrition (Symbiosis)
body functioning. These nutrients can The term symbiosis literally means
be categorised into two major groups: ‘living together’. Symbiosis is therefore a
organic and inorganic nutrients. Organic natural association between two or more
nutrients include carbohydrates which or organisms of different species. There
supply energy for body functions, fats or are three common types of symbiotic
lipids which constitute the major part of relationships which are mutualism,
cell membrane and stored form of body commensalism and parasitism.
energy. Other organic nutrients include
proteins, for growth and repair of body Mutualism
tissues, and vitamins for body defence. This refers to the association between
Inorganic nutrients include minerals and two living organisms of different species
water. The latter is a vital fluid required in which both benefit. Therefore, the
for chemical reactions to take place and association or relationship is beneficial
for transporting materials and minerals, to both partners. The cellulose digesting
which are essential for proper body bacteria and the ruminant herbivores are
functioning. an example of organisms, which show a
mutualistic relationship. These bacteria
5.3.1 Types of heterotrophic nutrition can only survive in anaerobic conditions
Heterotrophs obtain their food by found in the ruminant’s alimentary canal,
various ways. There are three forms and they feed on cellulose contained in the
of heterotrophic nutrition, namely host’s (ruminant's) diet. On the other hand,
saprophytic nutrition, symbiotic nutrition, ruminants cannot digest cellulose directly
and holozoic nutrition. but, as the cellulose digesting bacteria

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