A student investigates the effect of temperature on the rate of decay of grass clippings.
Bags of grass clippings are kept at different temperatures.
Which change would make the results of the investigation more valid?
Add the same volume of water to each bag of grass clippings.
Repeat each temperature three times and calculate the mean.
Use a balance that measures mass to two decimal places.
Measure the mass of each bag every day instead of every week.
111 exam-style questions on OCR GCSE Biology 4.1 Ecosystems, covering 4.1.1 Cycling of materials in ecosystems, 4.1.2 Microorganisms in cycling materials, 4.1.3 The carbon and water cycles, 4.1.4 Factors affecting decomposition, 4.1.5 Levels of organisation in an ecosystem, 4.1.6 Abiotic and biotic factors affecting communities, 4.1.7 Interdependence and competition, 4.1.8 Trophic levels, 4.1.9 Pyramids of biomass, and 4.1.10 Efficiency of biomass transfers. Each one has a worked solution and a mark scheme showing where the marks go.