Ecologists in the Swiss Alps investigated the rate of decomposition of subalpine fir needle litter placed in litterbags on the forest floor. Litter samples of equal initial mass were placed in bags of two different mesh designs: micro-mesh (which excludes soil fauna) and macro-mesh (which permits entry of soil mesofauna). At intervals of 8 weeks, a subset of bags was retrieved and the dry mass of the remaining needles was determined as a percentage of the original mass. The experiment was conducted over a period of 32 weeks.
The collected data are shown in the table below:
| Weeks | Dry mass of needle litter remaining (% of original mass) - Micro-mesh | Dry mass of needle litter remaining (% of original mass) - Macro-mesh |
|---|---|---|
| 0 | 100 | 100 |
| 8 | 91 | 85 |
| 16 | 83 | 72 |
| 24 | 76 | 61 |
| 32 | 69 | 52 |
Calculate the percentage decrease in the dry mass of the needle litter in the macro-mesh bag by week 32.
12 exam-style questions on Edexcel IGCSE Biology Cycles within ecosystems. Each one has a worked solution and a mark scheme showing where the marks go.