Big Idea:
Food Webs
Food Webs show the feeding relationships between organisms and are used to show the energy
transfer or energy flow in an ecosystem by indicating specifically who eats who. The
interconnecting relationships, illustrated by a food web, give an ecosystem its resilience. The
concept of Food Webs fits into the VCE Study design for Biology under Unit 2, Organisms and
their environment, Area of Study 2, Dynamic Ecosystems (VCAA, 2009).
What you intend
the students to
learn about this
idea.
Food webs show all the feeding relationships, and how individual organisms
can be part of several food chains at the same time. All these cross
connecting relationships give an ecosystem its resilience.
The feeding relationships between organisms can be shown as food chains.
The system of ‘who eats who’ in an ecosystem is a food chain and shows
the transfer of energy between organisms.
An organism that is part of a number of food chains in a food web is less
likely to be affected by the loss of one source of food.
Each feeding level in a food web is called a trophic level. An organism may
function at more than one trophic level in a food web.
1st trophic level includes producers (autotrophs) – source of energy (food) is
energy from sunlight captured during photosynthesis.
All other organisms are consumers (heterotrophs), which are dependent on
producers for their source of energy, which is provided in the form of food.
2nd trophic level includes primary consumers (herbivores) - source of
chemical energy (food) is from eating plants or other producers.
3rd trophic level includes secondary consumers (carnivores) - source of
chemical energy (food) is from eating plant-eaters.
4th trophic level includes tertiary consumers (top carnivore) - source of
chemical energy (food) is from eating predators.
There are several categories of consumers; herbivores, carnivores,
parasites (which feed on living organisms without killing them) and
omnivores. Scavengers, detritivores and decomposers all consume dead
organisms or organic material.
There are different types of food chains called predator-prey, parasite-host,
detritivore and decomposer food chains, depending on the relationships
between organisms.
Why it is important
for student to
know this.
To develop student knowledge and understanding that:
A food web is a complex network of many interconnected feeding
relationships.
Flow of energy along a food chain is a fundamental process in an
ecosystem.
Sustainable ecosystems rely on a continued supply and exchange of
energy from the sun.
Animals cannot make their own food, so they must eat other plants and/or
animals.
Chemical energy from one trophic level passes to organisms at a higher
trophic level.
The loss of an organism within the food web can have an impact on other
organisms at all trophic levels.
Relationships in ecosystems can be complex and finely balanced.
Human activities can have an impact on the relationships and interactions
within ecosystems.
What else you
know about this
idea (that you do
not intend student
to know yet).
Impact of bioaccumulation within a food web.
Implication of resource availability on populations.
Information about numbers of organisms at each trophic level can be shown
for an ecosystem through ecological pyramids.
Ecosystems differ in productivity because of factors that limit
photosynthesis, including temperature, sunlight, nutrients and water.
Impact of human activity and environmental issues on ecosystems such as
deforestation, oil spills, global change in CO2, greenhouse effect.
Implications of biogeochemical cycles including carbon, nitrogen,
phosphorus and water) on ecological systems.
Knowledge about
students’
thinking/difficulties
connected with
teaching this idea.
Requires prior knowledge and understanding of concepts such as
autotrophs, heterotrophs and photosynthesis.
Concepts presented in textbooks are often simplistic; therefore students
may find it difficult to grasp the intricacies of a food web.
Students may find it difficult to understand that an organism can change its
trophic level.
Students may believe the simpler the organism, the simpler the food it eats.
Therefore, they may believe as organisms increase in complexity the more
complex the food it eats.
Students may believe a population located higher on a given food chain
within a food web is predator of all populations located below it in the chain.
Detritivores, decomposers and scavengers are often left out of food chains
even though they are essential for nutrient cycling
Students may not know the food chains and webs in their local area
Students may think that varying the population will only affect the organisms
that are directly connected through the food web.
Students may think that food chains only involve predator and prey, no
producers, detritivores, decomposers .
Student may have difficulty in understanding that a smaller organism can
feed on a larger organism, as in parasite-host interactions or decomposers.
The life cycle of many parasites is complex. Students need to understand
that at different stages of development a parasite may feed on a separate
host species, and as such may be linked to a number of food chains.
Teaching

procedures (and 
particular reasons
for using these to
engage with this
idea).
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Speed date activity:
Each student is given an ‘identity’. Each identity is a concept that is to be
understood as part of this topic. ‘Identities’ could include; trophic levels,
producer organisms, primary consumer, secondary consumer, tertiary
consumer, ecosystem, food web, etc. Students are given time to research
their own ‘identity’ and then participate in a speed date with the rest of the
class. Each student has two minutes to talk about themselves (ie. their
‘identity’), discuss what you like, what you do for a living, where you like to
hang out, etc. Time is also given for the students’ date to ask questions.
After the allocated time each student swaps to a new date. This activity
gives students the opportunity to research and discuss one of the concepts
from this topic, it also allows them to listen and get involved in concepts
being described by other students.
Practical activity:
Provide student with a list of organisms that live in a pond community, with
details each organism’s food source. Ask student to construct a food web
and identify the organisms in various trophic levels. Specific questions
would also be provided. Have students then remove one of the organisms
from the food web. What are the implications? This activity gives students
the opportunity to consider trophic levels and the impact of relationships
within a food web.
Slowmation:
Students create a stop-motion animation to explain a food web.
Slowmation is a simplified way of making an animation with learners moving
models whilst taking digital still photos and playing them at 2 photos/
second to create a slow moving image. The explanation or story can be
enhanced by adding narration, text or music. This activity gives students
the opportunity to use ICT to illustrate their understanding of the concept.
Specific ways of
ascertaining
students’
understanding or
confusion around
this idea (including
likely range of
responses).
Asking directed questions to students in the class and having class
discussions on the topic.
Through construction of a food web, the teacher is looking to see if students
can put knowledge of food webs into practice.
Concept maps – students can make connections using key words and
phrases from this topic.
Apply understanding by giving examples of organisms in an ecosystem that,
for example, occupy different trophic levels.
The teacher is looking for demonstrated understanding of the concepts
covered.
Resources:
Binghampton University (2007), Common Ecological Misconceptions, Retrieved 3 August 2010,
from http://ecomisconceptions.binghamton.edu/foodwebs.htm
Biozone (2010). Biozone Biolinks. Retrieved on 2 August, 2010, from
http://www.biozone.com.au/biolinks/ECOLOGY.html#E5
Evans, B., Ladiges, P., McKenzie, J., Sanders, Y. (2007). Heinemann Biology 1, 4th Edition,
Harcort Education, Port Melbourne Victoria
Food Chains (2010), Food Chains, Retrieved 4 August, 2010, from
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FoodChains.html#Food_Webs
Kinnear, J., Martin, M. (2006). Nature of Biology Book 1, 3rd Edition, John Wiley & Sons, Australia
University of Wollongong (2010), Slowmation, Retrieved on 4 August, 2010 from
http://www.slowmation.com.au/
University of Maine (2008), Energy Transfer and Food Webs Background, Retrieved 3 August,
2010 from
http://misclab.umeoce.maine.edu/boss/classes/SMS_491_2008/week6/foodweb_bckgrnd.pdf
Victorian Curriculum Assessment Authority (VCAA), 2009. Biology, Victorian Certificate of
Education Study Design, retrieved on 28 June 2010 from
http://www.vcaa.vic.edu.au/vce/studies/biology/biologyindex.html
Wikipedia (2010). Food Chain. Retrieved 4 August, 2010, from
http://en.wikipedia.org/wiki/Food_web