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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
plant-eater
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
meat-eater
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
animal
- you needAatiny
microscope
to
that 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 eatand
fishfish
and krill
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
70 grammes
‘in’
= 100%
50 grammes
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
times
bigger means
means that
becomes
as long more
as
a easily
We can understand
theitsize
differences
if we
that
it is still
huge - it
In
the oceans,
both
the
plants
herbivores
are
small
bus and the
match
each
living
thing
to
familiar
objects.
Here,
we
Making
each
algaare
cellgreat
1000 size
times
bigger would
means
that it is
stretch
across
small.
There
differences
between
magnify
eachof1000
timesball
about
the
size
a
squash
herbivores and predators the Isle of Wight
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
NOTES for USERS
The material in this slide show is designed to support the teaching of science at Key Stage 2
A full description of the slide show, and linked activities for students, can be found on the
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www.national-aquarium.co.uk
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Training &
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