Good Science Victorian Curriculum Year 7

BIOLOGICAL SCIENCES
3.2
FOOD CHAINS
AND FOOD
WEBS
LEARNING INTENTION
At the end of this lesson I will be
able to describe interactions
between organisms in terms of
food chains and food webs.
KEY TERMS
ecosystem
a community of living and
non-living things
food chain
a path of energy through
an ecosystem
food web
a system of interlocking
food chains
1
All living organisms need energy to grow, repair damage
and reproduce. Without energy, an organism cannot survive.
Plants make their own food and energy, but other organisms –
including humans – must feed on other organisms to
gain energy.
The feeding relationships between organisms, and the
energy transfers in an ecosystem, can be shown in food
chains and food webs.
Food chains show the path of energy
in an ecosystem
Food chains are diagrams that show one possible path that energy
can move through an ecosystem. Energy is transferred between
organisms when they eat or are eaten.
Food chains always begin with a producer – a plant or microorganism
that can produce energy. This is because they provide the glucose for
all other organisms to feed on. Every ecosystem includes producers.
When you draw a food chain, you draw arrows between each
organism to show the direction that energy moves. In a food chain for
an Australian grassland ecosystem, a grasshopper gains energy from
grass, so you would draw an arrow from the grass to the grasshopper.
Figure 3.3 Each organism in a food chain
provides energy for the next organism.
LITERACY LINK
SPEAKING
Explain to another student the
difference between a food chain
and a food web. Ask them for
‘two stars and a wish’ – two
things you did well in your
explanation and one thing you
could have done better.
NUMERACY LINK
CALCULATION
Each level up in a food chain only
receives 10% of the energy of the
lower level. In Figure 3.3, the grass
would have to store 10 joules of
energy for the grasshopper to
receive 1 joule of energy. How
much energy would the grass
need to store to eventually
provide the wedge-tailed eagle
with 100 joules of energy?
Grass
Producer
The other organisms in the food chain – those that feed on organisms
to gain energy – are consumers. They can be described in terms of the
organisms they feed on.
Table 3.1 Types of consumer and how they obtain their energy
Consumer Obtains energy by … Examples
Herbivore … feeding on producers Koala, grasshopper
Omnivore
Grasshopper
Primary
consumer
Blue-tongue
lizard
Secondary
consumer
… feeding on producers and
other consumers
Eastern brown
snake
Tertiary
consumer
Sea star, most humans
Carnivore … feeding on other consumers Kookaburra, brown snake
Decomposer … breaking down dead matter Bacteria, fungi
Wedge-tailed
eagle
Quaternary
consumer
Organisms can also be described by their position in a food chain.
38 GOOD SCIENCE VICTORIAN CURRICULUM 7