Ecosystems

Food chains and food webs

Food Chains

What is a food chain?

Food chains show how plants and animals get their food (energy).  It shows how energy is passed from one organism to another, with the arrows representing the direction of energy flows.

The bottom of the food chain

Food chains usually start with a primary producer. Primary producers are organisms, such as plants, that produce their own food. They are called producers because all species in the ecosystem depend on them. The primary producers are then consumed by the primary consumers.

What eats the producers?

Consumers are all the organisms that can’t make their own food.   They get their energy by eating other organisms. Consumers that feed directly from producers i.e. organisms that eat plant or plant products are called primary consumers. An example of a primary consumer is the grasshopper.  Grasshoppers eat the grass.

The primary consumers are then in turn eaten by the secondary consumers in the next level of the food chain.  A secondary consumer is a consumer that gets its energy from other consumers. The snake is the secondary consumer in the diagram below. Finally the secondary consumers are eaten by the tertiary consumers, passing the energy to the final level of the food chain. The eagle is the tertiary consumer in the diagram below. Animals at this level of the food chain are generally carnivores and consume only other animals as their primary food source.

 

Figure 1: A Basic Food Chain
(Image source: http://en.wikipedia.org)

Herbivores, Carnivores and Omnivores

Animals can either be a herbivores, carnivores or omnivores:

  • Herbivores: Animals that eat plants (animals that are a primary consumer).
  • Carnivores: Animals that eat meat (animals that eat other animals).
  • Omnivores:Animals that eat both plants and animals (these are both herbivores and carnivores).

Therefore a food web is a more accurate way of showing the feeding relationships between plants and animals.

 

Food Webs

What is a food web?

A food web is a lot of food chains all put together to show how the plants and animals in an entire ecosystem rely on each other.  Figure 2 shows a basic food web for an arctic ecosystem. 

What does a food web show?

A food web describes the feeding relationships between species.  Food webs show the transfer of material, energy and food from one species to another within an ecosystem.

The arrows show the direction of the energy transfer within the ecosystem.  This means that the animal that ate another plant/animal has an arrow pointing to it.  Eg: The Arctic Birds eats the Arctic Cod.

 

Figure 2: A Simplistic Food Webfor an Arctic ecosystem
(Image source: http://commons.wikimedia.org/wiki/Image:Foodweb.png)

 


Outcomes
Year 7
Science Understanding - Biological Science

(ACSSU111)  There are differences within and between groups of organisms; classification helps organise this diversity

(ACSSU112)  Interactions between organisms can be described in terms of food chains and food webs; human activity can affect these interactions