Scientists investigate the decomposition of waste cotton fabric in water. Cotton fabric is made from plant material.
Two tanks contain the same volume of water and begin with the same concentration of decomposer microorganisms. Temperature and pH are kept the same. The dissolved oxygen concentration in each tank is maintained at the value shown for 15 days.
| Tank | Dissolved oxygen concentration (mg dm⁻³) | Initial dry mass of cotton (g) | Final dry mass of cotton (g) | Increase in dissolved carbon dioxide concentration (mg dm⁻³) |
|---|---|---|---|---|
| A | 8.0 | 40.0 | 28.0 | 11.2 |
| B | 2.0 | 40.0 | 36.5 | 3.4 |
Use the data to explain the differences between the results for the two tanks.
Predict how increasing the dissolved oxygen concentration in tank B to 8.0 mg dm⁻³ would affect its final dry mass, if all other conditions remained unchanged.
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.