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Modes of Nutrition
For most of these you need know little more than a
definition.
Where a named example is given you can expect to
have to give the example in the exam
Autotrophic nutrition
Autotrophs are organisms that are able to
synthesize their own organic substances using an external energy source.
The most obvious autotrophs are plants which use
the sun's energy to synthesize organic molecules; a process known as
photosynthesis
Some prokaryotes show a form of autotrophy known
as chemosynthesis. These bacteria derive their energy from chemical reactions
involving inorganic molecules and can use this energy to synthesize organic
molecules. The nitrifying bacteria of the nitrogen
cycle are good examples.
Heterotrophic nutrition
Heterotrophs are organisms that derive their
energy from ingested organic molecules.
The examples that follow are types of
heterotrophic nutrition.
Holozoic nutrition
Holozoic nutrition is that found among the
higher animals.
It can be broken down into:
- ingestion (taking into the body via the
mouth)
- digestion (mechanical and enzymatic
breakdown)
- absorption (in the small intestine)
- assimilation (use of the products of
digestion within the body)
- egestion (defaecation of unused components of
the food)
You need to know the adaptations shown by
a
- named
herbivore (cow)
- Note that the cow also takes part in a
mutualistic lifestyle with the anaerobic organisms in its rumen
- named
carnivore (dog)
- Note: humans are omnivores and show
characteristics of both of these groups so should NOT be used as an
example of either
Saprobiontic nutrition
Saprobionts (saprotrophs) are decomposers. They
get their food by digesting dead and decaying organisms.
Digestion is by the release of extracellular
enzymes on to the dead matter and absorption of the soluble products of
enzymatic digestion.
This lifestyle is typical of fungi and bacteria.
The fungus Rhizopus
is an example of a saprobiont
Parasitic nutrition
Parasites are organisms that have to live (for
at least some of their life cycle) in close association with another host
species.
Parasites can live:
- on outside of the host - ectoparasites
- within the host - endoparasites
Parasites derive their food from their host
Parasites usually harm the host
Parasites are usually very highly adapted for
their lifestyle. Taenia (tapeworm)
is an example of a highly adapted parasite
Mutualistic nutrition
Mutualism is similar to parasitism in that two
species are in very close association.
But different in that both species benefit from
the association
The
cow and its anaerobic rumen organisms are an example of mutualism
The nitrogen-fixing
bacterium Rhizobium and flowering plants of the family Papilionaceae
also display mutualism. These organisms are very important in the nitrogen
cycle
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