Lesson focus: How can a discarded object affect an animal far from where it was used?
Explain pathways from plasticA material made from long-chain molecules called polymers, used for bottles, bags and toys. waste to harm in ecosystems.
Build on earlier learning
MRS GRENConnect disruption of movement and nutrition to life processes.
You will be successful when you can…
- Describe transport into habitats.
- Explain entanglement and ingestion pathways.
- Distinguish exposure from effect.
- Identify confounding variables.
Words that carry the science
- entanglement
- Becoming trapped or restricted by material such as line or netting.
- ingestion
- Taking material into the digestive system.
- microplastic
- A plastic particle smaller than 5 mm.
- exposure
- Contact with a substance or hazard.
- confounding variable
- Another factor that differs and could affect the measured outcome.
Build causal explanations while respecting the evidence
01Waste moves through connected systems
Wind, drains and rivers can carry litter from where it was used into terrestrial, freshwater or marine habitats. Larger items can fragment into smaller pieces without fully breaking down chemically.
02Name the mechanism of harm
entanglementGetting caught up in something such as fishing line or netting. can restrict swimming, flight, feeding or escape. In simple steps: plastic wraps around the animal and traps it. The animal cannot move properly, so it may not be able to find food or escape from predators. This makes it less likely to survive. ingestionTaking food into the body through the mouth. can block the gut, create false fullness or expose tissue to associated chemicals, depending on material and dose.
03Test causal claims carefully
Finding plastic in an animal demonstrates exposureComing into contact with a hazard, for example by touching it, breathing it in or swallowing it.. Stronger evidence about harm measures outcomes, compares suitable groups and considers food, temperature, disease and habitat differences.
Evaluate a field comparison
Fish at site A contain more microplasticA tiny piece of plastic smaller than 5 mm. and grow more slowly than fish at site B.
- Identify the association: exposure is higher where growth is lower.
- Do not convert association directly into causation.
- Check alternatives such as temperature, food, oxygen, age and disease.
- Seek repeated sites, matched groups and dose–response evidence, or an experiment with a control group.
How to make the reasoning visible: The observation supports a hypothesis but does not isolate plastic as the cause.
Pathway and evidence map
For each claim, identify evidence for the link and an alternative explanation.
| Claim | Supporting observation | Alternative | Stronger evidence |
|---|---|---|---|
| Line restricts seal | Line wrapped around body | Pre-existing injury | Movement before/after safe removal |
| Ingestion reduces feeding | Plastic in gut + low stomach contents | Seasonal food shortage | Matched exposed/unexposed groups |
| Site A slows growth | Lower growth at polluted site | Lower temperature | Repeated matched sites |
| Fragments persist | Smaller pieces over time | Pieces transported away | Mass/particle tracking |
Why does plastic in a gut show exposure but not automatically harm?
Why compare more than one polluted and clean site?
Use the table. A seal has fishing line wrapped around its body. Why is this not enough on its own to prove the line injured it?
Check your understanding
Answer from memory, then check against the suggested answer.
What is entanglement?
What is ingestion?
What does exposure mean?
Name two ways plastic can harm wildlife.
What are microplastics?
Explain one route from a dropped wrapper to reduced feeding in a seabird.
Design a safer observational comparison of fish growth across sites.
Why might large plastic pieces turn into microplastics over time?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Animals such as turtles and seabirds can get tangled in plastic. Answer the parts to explain how this can stop them surviving.
What does the plastic do to the animal?
(1)What can the animal not do properly?
(1)Give one thing the animal needs to move for.
(1)So what happens to its chance of survival?
(1)Total for this question: 4 marks
Command word: Build a chain of steps from the plastic to the animal’s survival.