A food web joins all the food chains in an ecosystem. Arrows point the way energy flows, from the food to the eater. Every organism is a producer, a consumer or a decomposer, and decomposers include microorganisms.
A kookaburra eats lizards, grasshoppers, even small snakes. A food chain can only show one of those meals. How do you show all of them?
Food chains are a start. This lesson builds the whole web.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Practise: A few on your own, to check you have it.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: which way do arrows go?
ExploreTry it on the board and compare what happens with your prediction.
Explore: build a bush food web
Click a food, then the organism that eats it. The board tells you how many links there are. Don't forget the decomposers: what do fungi and bacteria feed on?
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Draw every feeding link, each arrow from the food to the eater.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: roles in the web
In your book: copy the bush web, with every arrow, and label each organism's role.
What is each organism's role in the bush web?
GrassIt makes its own food using sunlight.
GrasshopperIt eats a producer.
Kangaroo
LizardIt eats a primary consumer.
Dingo
Fungi and bacteriaThey break down dead grass, dead dingoes and droppings.
PractiseA few on your own, to check you have it.
Mix it up
Elaborate TypicalUse the same idea in a new context.
Elaborate: chain or web?
Elaborate WiderUse the same idea in a new context.
Elaborate: an Antarctic web
Krill eat phytoplankton. Small fish eat krill. Squid eat small fish and krill. Penguins eat small fish, krill and squid. Leopard seals eat penguins and small fish. Bacteria break down dead phytoplankton and dead leopard seals.
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Build the Antarctic food web. Phytoplankton are tiny drifting producers; krill eat them; the rest you can work out from the list.
Use the board. This ticks when you get there.
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
A food web joins all the food chains in an ecosystem.
Arrows point the way energy flows: from the food to the eater.
Producers make their own food; consumers eat other organisms (primary, secondary…); decomposers (fungi and bacteria, microorganisms) break down dead matter and wastes.
One animal can feed at more than one level.
For teachers
Students construct a food web with arrows in the direction of energy flow and identify producers, consumers and decomposers, including microorganisms (AC9S7U02, node 1, a hinge node). About 25 minutes.
I can construct a food web from a list of organisms.
I can draw arrows in the direction of energy flow.
I can identify producers, consumers and decomposers, including microorganisms.
Before class
A concept tutorial for introducing or revising the idea; it does not replace building a web from a real local ecosystem. Set the width with ?width=minimum, typical (default) or wider.
The hinge risk is arrow direction and missing decomposers. Every later node reads energy along the arrows.
Board notes: the board lays organisms out by feeding level automatically and draws decomposers with dashed borders. Wrong-way arrows turn red with a reminder; students click the same pair again to remove one. The decomposer links stand for dead matter and wastes.
Running the lesson
Engage: take a quick count of 'grasshopper to grass'. That is the 'eats' reading the board corrects.
Explore: the bush web has 8 links, including two to the decomposers. Ask what fungi feed on if students stop at 6.
Explain: the kookaburra question introduces feeding at more than one level.
In your own words: the labelled web is the evidence.
The hard part (on purpose)
Drawing arrows the way energy flows, not 'eats'. When an arrow points the wrong way, ask where the eater's energy came from.
When students get stuck
Arrows point from eater to food. Ask: Where does the energy in the grasshopper come from? Fix: From the grass: so the arrow goes grass → grasshopper.
No links to decomposers. Ask: What happens to a dead dingo? Fix: Fungi and bacteria break it down: an arrow from the dingo to the decomposers.
A student calls the kangaroo a producer. Ask: Does a kangaroo make its own food from sunlight? Fix: No: it eats grass. A primary consumer.
Stretch and support
Stretch: Rabbits were introduced to Australia. Add them to the bush web: what would they eat, and what would eat them?
Support: Give the organism list with each one's diet written beside it before the board.
Where it leads
Next: matter and energy flow (node 2): following the energy along the arrows and seeing how much is lost.
In class: a string web, each student an organism holding string to what they eat; cut one string and see who feels it.
What each step is for
Engage: which way do arrows go?: Students often draw arrows from eater to food ('eats'); committing first makes the energy-flow convention stick.
Explore: build a bush food web: Drawing each link, with wrong-way arrows flagged, builds the web structure and the arrow convention together.
Explain: roles in the web: Assigning every organism a role, including microorganisms as decomposers, is the node's checkpoint.
Mix it up: Where organisms get their food decides their role in a web. Fungi absorb food from dead material, which makes them decomposers.
Elaborate: chain or web?: Comparing the simpler model with the fuller one shows what each representation keeps and loses.
Elaborate: an Antarctic web: Building a second, unfamiliar web (marine) tests the structure rather than a memorised example.
Now you can
Construct a food web from a list of organisms.
Draw arrows in the direction of energy flow.
Identify producers, consumers and decomposers, including microorganisms.