3. Food chains What feeding relationships are shown here? Teacher notes
This illustration contains several discussion points relating to feeding relationships, including:
oak tree: the primary producer at the start of the food chain. Students should understand that producers make food through photosynthesis.
caterpillars: primary consumers, which gain energy by eating plant material.
birds: secondary consumers. They are larger than the caterpillars (primary consumers) but there are fewer of them.
cat: a tertiary consumer and the final stage in this food chain. It is larger than the birds (secondary consumers) but there is only one.

4. Feeding relationships
Teacher notes
This matching activity can be used at the start of a lesson to assess students’ existing knowledge of feeding relationships, or for revision purposes. It can be used to test understanding of terms introduced in KS3.

5. Energy transfer in the food chain
Teacher notes
This four-stage animated food chain shows a simple feeding relationship within an ecosystem. It can be used to introduce the topic and start students thinking about energy losses in the food chain. The direction of the arrow indicates the direction of energy flow.
See the ‘Photosynthesis’ presentation for more information about photosynthesis.

6. Why aren’t food chains very long?
This tiger is a top predator; the final level in a food chain.
Most food chains only contain four or five species, why is this?
Photo credit: © 2007 Jupiterimages Corporation
Energy is lost at all levels in food chains. Animals at the top of a long food chain would not get enough energy to survive.

7. Food chains and pyramids
What can pyramids show about energy transfer?
Teacher notes
This illustration contains several discussion points relating to food chains and pyramids, including:
Oak tree containing, caterpillars, shrews and an owl: This represents a food chain with an oak tree as the primary producer, caterpillars as primary consumers, shrews as secondary consumers and an owl as the tertiary consumer. The balancing act illustrates the dependence of organisms on a food supply. Although the amount of biomass decreases at each stage of the food chain, because this system is supported by one oak, representing this chain as a pyramid of numbers would result in a pyramid with a base narrower than its middle.
Ring master balancing on cows: This represents a food chain with cereal crops as the primary producer, cows as the primary consumer and humans as the secondary consumer. Students could be asked to consider if it would be more energy efficient for the human to eat the cereal crops directly.
Setting Sun: The Sun provides energy for photosynthesis, the process used by plants to make food.
Antelope and lions: The antelope are grazing on grass. They are being closely watched by a hungry-looking pride of lions. This represents a food chain with grass as the primary producer, antelope as the primary consumer and lions as the secondary consumer.

8. What are pyramids of numbers?
Pyramids of numbers are a quantitative way of representing food chains.
They record the number of organisms at each trophic level in a specified area.
What are the problems of representing food chains in pyramids of numbers?
Pyramids of numbers only give an accurate impression of the flow of energy in a food chain if the organisms are of similar size. Measuring the biomass at each trophic level can give a more accurate picture.

9. Numbers or biomass? Teacher notes
This activity provides illustrated examples of pyramids of biomass and pyramids of numbers. It could be used to allow students to draw comparisons between these two methods of representing food chains.

10. Understanding pyramids of numbers
In a pyramid of numbers, the length of each bar represents the number of organisms at each trophic level in a specified area.
As a single tree can support many organisms, this food chain produces an unbalanced pyramid.

11. Understanding pyramids of biomass
In a pyramid of biomass, the length of each bar represents the amount of organic matter – biomass – at each trophic level in a specified area.
At each trophic level, the amount of biomass and energy available is reduced, giving a pyramid shape.

12. Food chains and pyramids
Teacher notes
This completing sentences activity provides the opportunity for some informal assessment of students’ understanding of food chains and pyramids.

13. What is the main energy source for food chains?
Tasks
What is the main energy source for food chains?
Give one example of a food chain
What is a pyramid of numbers?
Give an example of pyramid of numbers
What are pyramid of biomass
Give an example of pyramid of biomass