IB1.19.1 Objectives
5.1 + 5.2 Pyramids of Biomass
WAL:
what pyramids of biomass show and how they are useful.
The
outcomes
• Can you interpret and construct a
pyramid of biomass in terms of organism
populations?
• Can you explain what relationship food chains
and pyramids of biomass show?
• Can you describe what a food chain shows?
Starter: Review your understanding of the previous
topic.
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IB1.19.1 Objectives
What do we get from food?
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IB1.19.1 Objectives
What do we get from food?
Energy!
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Energy in Food Chains
IB1.19.1 Objectives
Energy is stored in organisms as chemical energy.
When one organism eats another, this energy is passed on.
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Energy in Food Chains
IB1.19.1 Objectives
Not all of this energy is passed on, however. Some is lost in
Released in respiration to allow
other ways;
movement and to keep the rabbits
body temperature constant.
Only a small amount is
used for growth – this is
passed onto predators.
A lot of the chemical
energy is passed out as
undigested food.
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Energy in Food Chains
IB1.19.1 Objectives
Normally, there are fewer organisms as you go along
a food chain, because energy is lost at each stage.
10
3
1
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What is a food chain?
IB1.19.1 Objectives
A food chain is a diagram which shows the flow
of energy from one organism to another as they
eat one another.
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Pyramids of Numbers
IB1.19.1 Objectives
We can show these stages in a food chain using a pyramid
of numbers;
(Secondary
Fox
Consumer)
(Primary
Rabbits
Consumer)
Lettuces
(Producer)
Each level on a pyramid of numbers is called a trophic level.
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Pyramids of Numbers
IB1.19.1 Objectives
Pyramids of numbers do not always look like pyramids,
however. For example, one rose bush can feed many
aphids;
(Secondary
Ladybirds
Consumer)
(Primary
Consumer)
Aphids
Rose bush (Producer)
© Oxford University Press 2011
Pyramids of Numbers
IB1.19.1 Objectives
Pyramids of numbers do not always look like pyramids,
however. For example, one rose bush can feed many
aphids;
(Secondary
Ladybirds
Consumer)
(Primary
Consumer)
Aphids
Rose bush (Producer)
What would be a better way of
showing the flow of energy?
© Oxford University Press 2011
Pyramids of Biomass
IB1.19.1 Objectives
Pyramids of numbers do not take into account the size of
the organisms. A better way of showing the transfer of
energy is to use a pyramid of biomass.
This shows the mass of each organism at each trophic level.
Bigger organisms = more energy
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Pyramids of Biomass
IB1.19.1 Objectives
A sample of organisms is taken and they are dried out before
they are weighed.
How wet or dry the weather is can affect the mass of the
organisms, so their dry weight is taken to ensure that the
measurements of biomass are accurate.
Ladybirds 5g
Aphids 10g
Rose bush 1000g
(Secondary
Consumer)
(Primary
Consumer)
(Producer)
© Oxford University Press 2011
Pyramids of Biomass
IB1.19.1 Objectives
Pyramids of numbers do not take into account the size of
the organisms. A better way of showing the transfer of
energy is to use a pyramid of biomass.
This shows the mass of each organism at each trophic level.
Ladybirds 5g
Aphids 10g
Rose bush 1000g
(Secondary
Consumer)
(Primary
Consumer)
(Producer)
© Oxford University Press 2011
IB1.19.1 Objectives
How to construct
a pyramid of biomass
Construct a pyramid of biomass for the following food chain. Use the graph paper
below where 1 small square will represent 100kg:
Grass 
50,000
0.1kg
Rabbit
1,200
3kg

Fox
500
5kg
© Oxford University Press 2011
IB1.19.1 Objectives
How to construct
a pyramid of biomass
Construct a pyramid of biomass for the following food chain. Use the graph paper
below where 1 small square will represent 100kg:
Grass 
50,000
0.1kg
5000kg
Rabbit
1,200
3kg

3,600kg
Fox
500
5kg
2,500kg
© Oxford University Press 2011
IB1.19.1 Objectives
How to construct
a pyramid of biomass
Construct a pyramid of biomass for the following food chain. Use the graph paper
below where 1 small square will represent 100kg:
Grass 
5000kg
50 squares
100

Rabbit
3,600kg
100
36 squares
Fox
2,500kg
100
25 squares
Foxes
Rabbits
Grass
© Oxford University Press 2011