A student investigates how oxygen availability affects the decomposition of dead pondweed. Four identical containers each receive the same starting mass of pondweed and the same microbial inoculum. The student records the mass decomposed after 10 days.
Which pair gives the independent variable followed by a variable that must be kept the same?
Oxygen availability and mass decomposed
Temperature and water content
Oxygen availability and temperature
Mass decomposed and water content
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.