1. Food Chains and Webs
Year 8 Science

2. 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

3. 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.

4. 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.

5. 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.

6. Producers, Consumers and Decomposers

7. 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

8. 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

9. 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.

10. 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.

11. 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