A materials science research group evaluated the effectiveness of a new organic additive, BioShield-Y, designed to reduce the degradation rate of biodegradable polylactic acid (PLA) bioplastic buried in compost. Sixty identical bioplastic sheets were manufactured: thirty sheets were treated with BioShield-Y, and thirty sheets were left untreated. All sixty sheets were buried in the same compost bin under controlled temperature and humidity conditions for 90 days. At the end of the 90-day period, the percentage mass loss for each sheet was measured. The results showed that the sheets treated with BioShield-Y had a significantly lower percentage mass loss compared to the untreated sheets.
Explain why the group of untreated bioplastic sheets was necessary for this study.
689 exam-style questions on AQA A Level Psychology Scientific processes. Each one has a worked solution and a mark scheme showing where the marks go.