Understanding Food Webs

• Organsims in a food chain all depend on each other. 
• E.G - Grass is eaten by rabbits, which in turn are hunted and eaten by foxes. The grass captures the energy from sunlight to photosynthesise and makes glucose. The glucose provides engergy for the plant to grow. When the rabbit eats grass, the energy left in the grass is transferred to the rabbit. When the fox eats a rabbit, the remaining energy in the rabbit is transferred to  the fox.

Changes in the number of one organism in a food chain affects other organisms in the food chain!

• The number of plants in an ecosystem can be affected by the amoutn of rain, sunlight, minerals and space available to grow.
• The number of animals can be affected by the amount of food, habitats, mates, water and diseases.

Harbour seals, harp seals and Artic terns all fed on Artic cod. If the Artic cod catches a disease and diese, the Artic tern and harp seals will eat more of their other prey. The harbour seal only eats Artic cod, so they will die too. This means that the cod will not eat amphipods and copepods, so there will be more food for the humpback whale and Artic char, and their populations will increase.

Most animals eat many different things and are involved in many different food chains. These food chains can be put together in a Food Web, which shows how the food chains are connected. Food webs can sometimes be very complex!

In a food web, there are different rankings. These are listed below.

• Produces make their own food.
• Primary Consumers eat producers
• Secondary Consumers eat primary consumers
• Tertiary Consumers eat secondary consumers.

These rankings are called Trophic Levels. The trophic levels of an organism is the position it occupies in a food chains.

The arrows in a Food Web indicate the Direction of the Energy Flow.

• Food chain
• Food web
• Primary consumer
• Secondary consumer
• Tertiary consumer
• Trophic level