Read a food web as connected chains
A food web combines interconnected food chains; trace each arrow carefully because an organism may have several food sources or consumers.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Read energy-transfer arrows and distinguish energy from matter in the 19.1 Energy flow pathway.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What makes a food web different from a single food chain?
What you will learn
- Interpret a network of feeding links
- Identify trophic positions along a stated route through a web
Follow one path at a time
A food web is a network of interconnected food chains. Each arrow still points from food organism to consumer. To answer a question about a particular organism, trace the incoming arrows to see what it eats and outgoing arrows to see which organisms may eat it. A web can show multiple routes from producers to top consumers.
An organism can appear at more than one trophic position if it feeds on different organisms. State the route you used before assigning a level. Do not assume that every prey population is equally important or that every possible link is shown.
Predict with the web, then bound the claim
If a prey population changes, a predator that feeds on it may be affected. Other prey, competitors and environmental conditions can modify the outcome. A food web helps identify possible direct and indirect links; it does not provide population numbers or prove how large an effect will be.
When interpreting a change, name the link first, then phrase the result as a possible consequence unless the question gives data establishing a measured response. Check whether an organism has alternate food sources.
Sources for this lesson
Pause and explain
An organism eats two different consumer species in a web. What should you do before assigning its trophic position?
Worked example
A web has grass → grasshopper → frog → hawk and grass → rabbit → hawk. Name two consumers that may eat grass and one prey of the hawk.
Show the worked solution
- Trace arrows out from grass.
- Trace arrows into hawk.
Answer Grasshopper and rabbit may eat grass. The frog or rabbit may be prey of the hawk in the routes shown.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
In a web, algae → water fleas → trout and algae → insect larvae → trout. Name the producer and two possible prey of trout.
Give me a hint
Trace incoming arrows to trout, then identify the producer.
Compare my reasoning
- Algae is at the beginning of both routes.
- Both water fleas and insect larvae point towards trout.
Algae is the producer. Trout may eat water fleas and insect larvae in the web shown.
Look for these in your work
- Producer found
- Both links interpreted
A web shows seeds → mice → owls and seeds → mice → foxes. If mouse numbers fall, state one possible effect and one reason not to treat it as certain.
Give me a hint
Follow the links from mice to predators and consider other food.
Compare my reasoning
- Owls or foxes may have less of this prey.
- The web or habitat may provide alternative food or other influences.
Owls or foxes could be affected because mice are a food source; the size or certainty of the effect cannot be decided without considering alternative prey and other evidence.
Look for these in your work
- Direct link traced
- Uncertainty bounded
An omnivore eats plants and herbivores. Explain why it can occupy more than one trophic position.
Give me a hint
Compare its route when eating a producer with its route when eating a consumer.
Compare my reasoning
- Plants are producers.
- Herbivores are consumers that feed on producers.
When feeding on plants the omnivore can be a primary consumer; when feeding on herbivores it can occupy a higher position.
Look for these in your work
- Routes distinguished
- Position explained
Common mistakes
- Reading arrows as “eats” in the arrow direction
- Treating a food web as one long chain
- Predicting a certain population response without considering other links
What can you explain now?
What makes a food web different from a single food chain?
Compare with the explanation
It connects several feeding chains into a network
The network shows more than one linked feeding route.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do arrows help you read a food web, and why can one organism have more than one trophic position?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.