The organisms within food chains can
be divided into different categories, producers, consumers and
scavengers. They can also be classified by their trophic level or
position on the food chain. Any organism that feeds on a plant is
called a first order consumer or heterotroph. Producers are also
known as autotrophs because they are found on the bottom level of a
Plants, or producers, take the energy from sunlight
and use it to carry out photosynthesis - change carbon dioxide into
glucose or other sugars. These sugars contain carbon carbon bonds.
As consumers eat producers they break these bonds which release
pure energy for further use.
Light energy --> chlorophyll -->
photosynthesis --> glucose --> converted into other
carbohydrates (eg glucose, sugars) --> eaten by consumers which
use the energy.
Algae is a producer which also uses photosynthesis,.
Cyanobacteria or the dreaded "blue green algae" effects many rivers
by clogging waterways as the plants reproduce rapidly. Bacteria is
another common autotroph (producer), taking energy from a wide
variety of sources to form sugars. Bacteria can be found around
deep-sea vents, using the energy from the chemicals coming out of
the earth's interior to create sugars. Bacteria also live deep
underground and use similar sources to convert carbon dioxide into
Consumers eat producers or other lower order
consumers. For example, an organism which feeds on a first order
consumer is called a second order consumer. A decomposer breaks
down any dead organisms with the most common being fungi and
bacteria. They convert animal and plant matter back into
An example of these levels in a food chain is:
Sun --> producer (plant) --> first order
consumer (herbivore) --> second order consumer (carnivore)
--> third order consumer (carnivore) --> bacteria
When these categories are applied to the wallaby food
Grass is eaten by a wallaby is
eaten by a dingo is decomposed by
The first order consumer is the Wallaby as it eats
plant matter. The second order consumer is the Dingo because it
eats the wallaby. The decomposer, bacteria, breaks down any dead
Another method of describing a consumers' role in the
food chain is to group them according to the source of their food.
Animals which eat plants are called herbivores, those which eat
other animals carnivores and those which eat both plants and
Herbivores feed on a primary trophic level so they
are also known as autotrophs and producers. Carnivores feed on the
secondary or higher trophic level and are therefore heterotrophs or
a higher order consumer. Omnivores feed on all trophic levels.