Pyramids Of Number & Biomass

D. Crowley, 2008

Pyramids Of Number & Biomass

To understand pyramids of number and biomass

Tuesday, April 18, 2023

Big Mac

Where does the energy in a Big Mac come from?

It comes from the cows that make the

burger

It comes from the sugar in the

burger sauce

There is no energy in a big

Mac – that is why they are bad for

you

It comes from the sun

It comes from the green parts

because they are healthier

Big Mac

All the energy within our food originates from the sun – transferred through food chains...

It comes from the sun

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)

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

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

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.

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

Pyramids

Complete the pyramids worksheet

Questions

1. Draw out, and explain why this pyramid looks a funny shape: -

Look at the food chain below: -

grass grasshopper frog grass snake 100’000 500 5 1

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

Lettuce plants

Rabbits

Fleas

Questions

1. Pyramid of number: many fleas can feed of just one rabbit

2.

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

Lettuce plants

Rabbits

Fleas

Grass

Grasshoppers

Frog

Grass snake

Fox & Sun

Explain as fully as you can why a fox is reliant on the Sun...

Fox & Sun

Producers (e.g. grass) grow via photosynthesis, getting their energy from the Sun

This energy is used to allow the producer to grow (increase in biomass), eventually being passed on to consumers (e.g. a rabbit) when they eat it

When a fox eats the consumer energy is again passed on, so completing the energy chain from Sun to producer to consumer to secondary consumer (fox)

Sun → Grass → Rabbit → Fox