Pyramids of Number & Biomass
Science: KS3, topic 1.3.14
Pyramids of Number and Biomass
Ecological pyramids are sometimes called a trophic pyramid. Ecological pyramids model and visualise what is happening in a food chain.
Food chains and webs
- A food chain is a model that shows how energy flows through an ecosystem.
- A food chain shows which organisms eat one another.
- Food chains use trophic levels to represent which organisms eat one another.
- A food web is a series of food chains that overlap.
Producers and primary consumers
- A food chain exists between grass, rabbits, and foxes.
- Grass is the producer in this food chain.
- Grass gets energy from the sun.
- The rabbit is the primary consumer in this food chain.
- Primary consumers are normally herbivores.
- Primary consumers eat producers.
Secondary consumers
- The fox is the secondary consumer in the food chain with grass, rabbits and foxes.
- Secondary consumers are normally carnivores.
- Secondary consumers eat primary consumers.
- The predator at the end of the chain is also called the apex predator.
Pyramids of number
- Pyramids of number represent the number of organisms in each trophic level.
- The producer is at the bottom of the pyramid.
- If the producer is a large organism like a tree, it will not be at the bottom of the pyramid.
- Large organisms like trees can feed lots of small primary consumers.
- The trophic levels go up in steps in the pyramid.
- The width of each trophic level represents the number of organisms at that level.
Pyramids of biomass
- A pyramid of biomass shows the total mass of the organisms in a trophic level.
- Pyramids of biomass show mass in grams or kilograms.
Test yourself on Pyramids of Number & Biomass
Which of these would normally be at the bottom of a food pyramid?
Select the true statement in each pair.
Name the two types of ecological pyramid used to model a food chain.
In a normal pyramid of number for the grass, rabbit, fox food chain, which organism would usually be more numerous?