Food Chains and Webs
Year 8 Science
Producers, Consumers and Decomposers
Living things can be classified into
three groups according to their role in
the ecosystem:
These three groups are
• Producers
• Consumers
• Decomposers
Producers
Producers: These are organisms that produce
their own food from their non-living
environment. For example, plants during
photosynthesis produce sugars and starch
from carbon dioxide and water via energy
from the sun.
Because plants can produce their own food
they are called producers.
Consumers
Consumers: These are organisms that eat other organisms
or their products. Animals are unable to make their own
food and must consume (eat) plants or other animals to
obtain food. Animals are therefore called consumers.
Animals can be classified into three categories:
• Herbivores - Those animals that eat plants.
• Carnivores - Those animals that eat animals.
• Omnivores – Animals that eat both plants and animals.
Decomposers
Decomposers: These are the bacteria and fungi
which break down plant and animal remains into
simple compounds and make them available
again for use by plants and animals. Compost
heaps are an example of decomposers at work breaking down food scraps and plant cuttings
into a natural fertiliser for garden beds.
Producers, Consumers and Decomposers
Food Chains
The feeding relationships between producer and consumer
organisms can be written down in a series of steps called a
food chain. Here is one example of a food chain:
Grass → grasshopper → kookaburra
The food chain shows how when food is eaten energy is
passed from one living thing to another. The arrows
indicate the direction of flow of energy from one organism
to another. This food chain shows producers and
consumers.
The grass is the producer
The grasshopper is called the first order consumer
The kookaburra is called the second order consumer
Food Chains
When we write food chains we often also
include the ‘sun’ as this is where all food
chains start:
Sun → Grass → grasshopper → kookaburra
In your Core Science 2 text
(page 143) is an example of
several levels of consumers
associated with you eating a
dinner of fish and chips. In
this example you are the
fourth-order consumer.
Food Webs
In a typical ecosystem there are many different
food chains and paths associated with the
consumers and producers.
Each animal eats a variety of different foods
(other animals or plants) and is also the target of a
number of different predators.
Joining a number of food chains together produces
a food web, which outlines who eats whom in the
whole ecosystem.
Food webs and food chains
In this food web we can see three food chains:
• Algae on rock → snail → large fish
• Water plant → small fish → large fish
• Algae on rock → snail → small fish → large fish