Year 9 Science · Unit 2 · Lesson 18
Foundation Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
All bioplastics break down in any conditions, including home compost bins and the ocean.
Correct it:
A life cycle assessment looks at a product’s impact from its raw materials, through making and using it, to its disposal.
Correct it:
UV light breaks plastic into smaller pieces, but the pieces are still plastic.
Correct it:
Polyethylene bags are not biodegradable because they are made from plant materials that microbes cannot digest.
Correct it:
Soil bacteria make enzymes that easily break the C–C backbone of polyethylene.
Correct it:
1. Define “biodegradable”. Explain why polyethylene is not biodegradable, using the term “C–C backbone”.
Odd one out
In each group, one item does not belong. Write the odd one out and your reason.
| # | Group | Odd one out and reason |
|---|---|---|
| 1 | PLA · starch-based foam · cellulose film · polyethylene | |
| 2 | bacteria · fungi · UV light · earthworms | |
| 3 | moisture · darkness · warmth · oxygen |
2. Sunlight slowly breaks a plastic bag into smaller and smaller pieces. Explain why this does not solve the problem of plastic pollution.
Class investigation: the burial test
A class cut four materials into squares with a mass of 2.00 g each. They buried the squares in damp garden soil at room temperature. After 8 weeks they dug them up, rinsed and dried them, and weighed them again.
| Material | Mass after 8 weeks (g) | Mass lost (%) |
|---|---|---|
| Paper | 0.90 | |
| PLA cup (labelled “compostable in industrial facilities”) | 1.98 | 1 |
| Polyethylene bag | 2.00 | 0 |
| Cotton cloth | 1.40 |
Source: sample class results.
3. Calculate the percentage of mass lost by the paper and by the cotton cloth. Write your answers in Table 1.
4. The PLA cup is made from plants, yet it hardly changed. Use its label and Lesson 18 to explain why.
5. The class buried only one square of each material. Explain why this makes the results less reliable, and suggest one improvement.
6. A weekend market plans to hand out “biodegradable” bags. Write a short note to the market organisers explaining what biodegradable means, what conditions it needs, and why a biodegradable bag that ends up in the sea or a sealed landfill may still not break down.