A food scientist carries out two trials using equal masses of moist, cooked mushroom.
In trial 1, sample R is stored at 6 ∘C6\,^{\circ}\text{C}6∘C in packaging that allows air to enter. Sample S is vacuum packed and stored at 18 ∘C18\,^{\circ}\text{C}18∘C. Sample S decomposes more slowly than sample R.
In trial 2, new samples are stored at the same temperatures, but both are exposed to air. Sample S now decomposes faster than sample R.
The decomposers' optimum temperature is above 18 ∘C18\,^{\circ}\text{C}18∘C.
Which statement explains the results of both trials?
In trial 1, lack of oxygen limits respiration by aerobic decomposers on S; in trial 2, the higher temperature increases their enzyme activity.
In trial 1, vacuum packing kills the decomposers on S; in trial 2, decomposers carried in the air grow faster on S at the higher temperature.
In trial 1, vacuum packing draws water out of S; in trial 2, S absorbs moisture from the air so its decomposers grow faster.
In trial 1, the low temperature kills most decomposers on R; in trial 2, decomposers on S survive the higher temperature and grow faster.
101 exam-style questions on Edexcel GCSE Biology 9.3 Material cycles and decomposition, covering 9.3.1 Cycling of materials through ecosystems, 9.3.2 The carbon cycle, 9.3.3 The water cycle, 9.3.4 The nitrogen cycle, 9.3.5 Indicator species and pollution, 9.3.6 Decomposition in preservation and composting, and 9.3.7 Rate changes in decay of biological material. Each one has a worked solution and a mark scheme showing where the marks go.