What happens to plastic when you throw it away?

Lesson overview

In this chemistry Key Stage 3 (KS3) lesson, students investigate rates of decay. The lesson is focused on students designing their own investigation. Included are teacher resources allowing students to test how a conventional plastic bag decays compared to a compostable bag (using a potato as a substitute), in different conditions.

Learning outcomes
  • Recognise that most plastic ends up in either landfill or the sea
  • Order materials based on the time they take to degrade
  • Describe alternatives to using plastics
  • Create an investigation on how to increase the speed of decay
Lesson steps
  1. The best thing about plastic (10 mins)
    The lesson starts with students considering what makes plastic such a great material by looking at common plastic items.
  2. What happens to plastic in the ocean (15 mins)
    Students plot the time it takes for different types of marine litter to biodegrade and discuss how this should influence our choice of materials.
  3. Plastics and turtles (10 mins)
    Turtles are one of the species where there is a good body of evidence for the impact of plastics. Students create statements on the harm caused by plastics using sentence segments.
  4. Do we know enough (20 mins)
    Action on plastics is being implemented by many cities and countries. Students need to evaluate the current evidence and decide whether drastic action is now required.
  5. The worst thing about plastic (5 mins)
    As a plenary, return to the starter and decide what the worst thing about plastic is.