A researcher measures the decay of two samples of dead wood collected from different sites.
Sample P has a starting dry mass of 18 g and sample Q has a starting dry mass of 30 g. For each sample, the researcher records the time taken for the dry mass to decrease by 3 g.
The researcher uses 1÷time1 \div \text{time}1÷time to rank the samples by their observed rate of dry-mass loss.
Which judgement is correct?
The ranking is invalid because the samples did not have the same dry mass at the start.
The ranking is valid because each recorded time is for the same 3 g loss in dry mass.
The ranking is invalid because 1÷time1 \div \text{time}1÷time leaves out the mass lost, so it is not a rate.
The ranking is valid for percentage mass loss because both samples lose 3 g.
83 exam-style questions on AQA GCSE Biology 7.2 Organisation of an ecosystem, covering 7.2.1 Levels of organisation, 7.2.2 How materials are cycled, 7.2.3 Decomposition, and 7.2.4 Impact of environmental change (HT only). Each one has a worked solution and a mark scheme showing where the marks go.