An ecology student investigated the rate of decomposition of fallen oak leaf litter by measuring the percentage of dry mass remaining over a period of 60 days.
The student used the following method:
Table 1 shows the measurements obtained at 12∘C12^\circ\text{C}12∘C:
Time (days)0102030405060Dry mass remaining (%)100989280655245\begin{array}{|c|c|c|c|c|c|c|c|} \hline \text{Time (days)} & 0 & 10 & 20 & 30 & 40 & 50 & 60 \\ \hline \text{Dry mass remaining (\%)} & 100 & 98 & 92 & 80 & 65 & 52 & 45 \\ \hline \end{array}Time (days)Dry mass remaining (%)0100109820923080406550526045Answer the following questions:
Suggest how the student could maintain the soil at a constant temperature of 12∘C12^\circ\text{C}12∘C for the 60-day period.
State one variable, other than temperature, that the student should control to ensure a valid comparison between the two trials.
If these results are plotted on a graph with the percentage of dry mass remaining on the y-axis and Time (days) on the x-axis, describe how the curve representing the leaf litter kept at 20∘C20^\circ\text{C}20∘C would compare to the curve for 12∘C12^\circ\text{C}12∘C.
40 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.