| Date | November 2015 | Marks available | 3 | Reference code | 15N.3.SL.TZ0.20 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 20 | Adapted from | N/A |
Question
Explain how living organisms can change the abiotic environment during primary succession.
Markscheme
a. lichens secrete chemicals/acid which break down inorganic material/rock;
b. lichens/plants/litter change pH of the soil (which prevents/assists some species to establish);
c. organisms increase the mineral/organic/humus content of the soil when they decompose;
d. (organic matter and humus) can increase water retention;
e. plant (roots) can bind soil preventing erosion / break down soil particles;
Examiners report
Most candidates had some idea about succession but some referred to secondary succession and many answers came without explanations.
Syllabus sections
Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics) » C.2 Communities and ecosystems
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