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Science Training &
Education Partnership
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Food chains and food webs ‘who eats whom’
Food chains and food webs
What goes in, what comes out?
Sizes and numbers
Summary
Food chains and food webs
What goes in, what comes out?
Sizes and numbers
Summary
Food chains show how food passes from
one living thing to another
All food chains start with a Plant
Plants can make their own food, using
sunlight
FOX
RABBIT
An animal that eats
other animals
GRASS
An animal that
eats plants
A plant - makes its own
food
The arrows
show the food
chain
FOX
RABBIT
An animal that eats
other animals
GRASS
An animal that
eats plants
The plant is a
‘producer’
A plant - makes its
PRODUCER
own food
FOX
RABBIT
An animal that eats
other animals
GRASS
An animal that
CONSUMER
eats plants
A plant - makes its
PRODUCER
own food
The rabbit is a
‘consumer’ - a
herbivore or planteater
FOX
RABBIT
An animal that eats
CONSUMER
other animals
GRASS
An animal that
CONSUMER
eats plants
A plant - makes its
PRODUCER
own food
The fox is also a
‘consumer’ - a
predator or meateater
Food chains work in the same way in the
sea ...
… but the plants and animals look a bit
different!
FISH
COPEPOD
ALGAE
Out in the ocean, there is
no grass or trees
An animal that eats
other animals
The plants are tiny ALGAE
A tiny
that
- you need
a animal
microscope
to
eats plants
see them
Microscopic plants make their own food
This is a food chain
in the ocean
FISH
COPEPOD
ALGAE
Out in the ocean, there is
no grass or trees
CONSUMER
PRODUCER
CONSUMER
The food chain won’t stop there ...
In most habitats, there are several food
chains
These are linked together to form a
Food Web
Food webs can be quite complicated
Here is one from the ocean around
Antarctica …
Seals eat squid
Squid eat fish
and krilland fish
Fish eat krill and
copepods
A simple food chain
whale eats krill eats
algae
Copepods also eat algae,
and are eaten by krill
This food web contains 7 types of living things, and 9 food chains
Food chains and food webs
What goes in, what comes out?
Sizes and numbers
Summary
Not all food eaten by an animal is turned
into new body tissue - ‘growth’
In fact, for most animals, very little food
contributes to growth
Some cannot be digested, and is lost
Much food is used to provide energy
An example: krill feeding on algae
This leaves 10
grammes of food that
can be used for
growth
70 grammes of algae
eaten per day
50 grammes of food are used
to provide energy for
swimming and catching more
food
10 grammes - about
15% - is indigestible
10 grammes to
growth
= 15% of food eaten
50 grammes
70 grammes
‘in’
= 100%
plus
10 grammes
‘to waste’
= 85% of food eaten
The same thing happens at every step
along the food chain
Look at the food web from Antarctica ...
A large blue whale will eat 3
tonnes of krill each day
The amount of growth will be
120 kilogrammes -96% of
the food has ‘gone to waste’
Food chains and food webs
What goes in, what comes out?
Sizes and numbers
Summary
The rate at which animals grow is often
related to their body size
FOX
RABBIT
GRASS
On land,
herbivores and
predators are
often similar in
size
Making the whale 1000
Making the krill 1000 times bigger
means that
means that
becomes
as longtimes
as a bigger
We can understand
theitsize
differences
more
easily if we
it is still hugeare
- it would
In
the oceans,
both
the
plants
herbivores
small
bus and the
match
each
living
thing
to
familiar
objects.
Here,
we
Making
each
algaare
cellgreat
1000 size
times
biggerstretch
means
that itthe
is Isle of
across
small.
There
differences
between
magnify
eachof1000
timesball
about
the
size
a
squash
Wight
herbivores and predators
We have seen that most food eaten by
consumers is either not digested or
converted to energy
Only a small amount is converted to
growth
This happens at each link in the food
chain
The shortest food chain in the Antarctic
food web has two links
LOSS
LOSS
For 100 tonnes of algal growth ...
… there are 15 tonnes of new krill
growth ...
… and there are only 600 kilogrammes
of new whale growth
The longest food chain in the Antarctic
food web has five links
LOSS
LOSS
LOSS
LOSS
LOSS
Now, for 100 tonnes of algal growth ...
… and there is only 1 kilogramme of
new seal growth
99.999% of the algae eaten by the
copepods has been lost
In the food chain with more links, more
producer growth is lost
Food chains and food webs
What goes in, what comes out?
Sizes and numbers
Summary
You have seen that -
A food chain links plants
and animals in a habitat
All food chains start with a
plant = producer
You have seen that -
Food webs on land and in
the ocean are similar
In the ocean, plants and
herbivores are small
You have seen that -
Most food in a food chain is
turned into energy and lost
Long food chains waste
more food than short ones
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NOTES for USERS
The material in this slide show is designed to support the teaching of science at Key Stage 1
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