1. Pyramids Of Number & Biomass
Noadswood Science, 2011

2. Pyramids Of Number & Biomass
Tuesday, April 30, 2019
Pyramids Of Number & Biomass
To understand pyramids of number and biomass

3. Food Chains & Webs
A food chain shows what eats what in a particular habitat - the arrow points in the direction of the energy flow, e.g.
Here the grass (producer) is eaten by the vole (primary consumer) which is eaten by the barn owl (secondary consumer)
Energy is passed along the food chain, so the number of organisms decreases from one trophic level to the next (as energy is lost)

4. Food Chain
Food chains are never very long (usually only 4/5 stages at most) – why is this?
Remember the arrow shows the energy being transferred from one organism to the next - between each step energy is lost in a variety of ways, including: -
Growth of the organism
Reproductive costs
Lost through waste products (poo)
Lost through heat
This is why food chains are never that long - as lots of energy is lost from one stage to the next

5. Food Chain

6. Food Web
In most habitats organisms normally eat / are eaten by more than one other organism
To represent this we use food webs (like food chains but they interlink with one another), e.g. a pond
Here the producers are the pondweed and the microscopic algae
Mayfly nymphs eat the pondweed and microscopic algae, and freshwater shrimp eat the microscopic algae
Dragonfly nymphs and brown trout eat the mayfly nymphs and freshwater shrimp
Brown trout also eat the dragonfly nymph!

7. Key Words Producers – green plants make food by photosynthesis
Primary consumers – usually eat plant material (they are herbivores)
Secondary consumers – usually eat animal material (they are carnivores)
Predators – kill for food (they are either secondary or tertiary consumers)
Prey – the animals that predators feed on
Scavengers – feed on dead animals
Decomposers – feed on dead and decaying organisms, and on the undigested parts of plant and animal matter in faeces

8. Balance
Populations in a food chain are dependent upon one another – there is a balance between the producers and consumers in the food chain
For example if there are lots of giraffes they will eat a large quantity of the trees and shrubs until there may be insufficient amounts to support them. If this is the case many will begin to starve and die
Fewer giraffes means less food for lions, which will eventually see a population decrease
Less giraffes will allow more shrubs and tress to survive, so the giraffe population recovers, leading to the lion population recovering, until the process repeats itself…

9. Population
The population of each organism in a food chain can be shown in a sort of bar chart called a pyramid of numbers
The more organisms there are, the wider the bar. The producer in the food chain always goes at the bottom of the pyramid of numbers
E.g. clover  snail  thrush  hawk

10. Pyramid Of Number
Pyramids of number show how many organisms there are in a habitat
A pyramid of number for the food chain below might look like this: -
If there were 200 grass plants; 25 voles; and 1 barn owl

11. Pyramid Of Number
Pyramids of number show how many organisms there are in a habitat
However they may not always look like classical pyramids: -
Here there are much more caterpillars than there are oak trees which is why the pyramid is oddly shaped.

12. Pyramid Of Biomass Biomass means the amount of biological material
The pyramid shows the amount of biological material at each level
This means the oak tree has the most biological material whilst the sparrow hawk has the least

13. Pyramids
Complete the pyramids worksheet

15. grass  grasshopper  frog  grass snake
Questions
1. Draw out, and explain why this pyramid looks a funny shape: -
Look at the food chain below: -
grass  grasshopper  frog  grass snake
100’
2. Draw a pyramid of numbers for the food chain
3. Write down the names of: the top predator; the producer; the consumers; the primary consumer; the tertiary consumer; the herbivores; the carnivores
Fleas
Rabbits
Lettuce plants

16. Questions 1. Pyramid of number: many fleas can feed of just one rabbit2.
3. Top predator – grass snakes;
Producer - grass;
Consumers – grasshoppers, frogs, grass snakes;
Primary consumer - grasshoppers;
Tertiary consumer – grass snakes;
Herbivores - grasshoppers;
Carnivores – frogs, grass snakes
Fleas
Rabbits
Lettuce plants
Grass snake
Frog
Grasshoppers
Grass